Alpha Centauri 2

Community => Recreation Commons => Topic started by: Buster's Uncle on July 05, 2016, 03:59:50 PM

Title: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 05, 2016, 03:59:50 PM
SO - I just saw some NASA Kepler thing from May that was explaining occultation detection at the outset, and I wanted to ask about something I've wondered for quite a while; it's obvious that the technique has the severe limitation of only being any good when the system's plane of ecliptic -or at least the orbit of any given individual planet there- lines up in the same direction we're looking from in at least one dimension - of course.

Casual observation tends to confirm that earth's rotation is somewhat lined up with the galaxy's plane, the Milky Way being not terribly far off the equator in our sky and our rotation being roughly in the same plane as the solar system's ecliptic.  1.) How common does that seem to be in other systems, the ecliptic being sorta lined up with the rest of the galaxy, noting plenty of exceptions in our own solar system (most obviously that the moon so rarely lines up exactly with the sun relative to any particular terrestrial POV, but also thinking of Neptune and Pluto), both in orbit and rotation?  And 2.) given the local group of stars being not on a flat plane at all in relation to each other -I believe Wolf 359, for an example of a dinky close star only famous for a fake Star Track Borg battle, is considerably to our galactic north, as Alpha Centauri is south to the extent it's never in our sky in the rightside-up proper American part of the globe- how frequently is occultation detection useful on a relatively local scale?  -It seems intuitive that a north-south deviation from our viewing angle becomes less significant the further away the star being observed is, though of course resolving the light dip becomes more difficult with distance and relative dimness and balances out at some relative limit...
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 05, 2016, 04:23:08 PM
So, there's an angle of about 60 degrees between the galactic plane and the plane of the ecliptic, which means we're not really all that well lined up with it. Wonky configurations relative to the galactic plane seem to be pretty normal, which we know because we basically see planets as often as we should. That is, if extrasolar ecliptics are distributed randomly, then only a small percentage of stars should be in line with us, and observation says we don't see more than that percentage with planets.

The real limitation is that it's much less efficient to look up or down or out, because we are basically situated two thirds of the way out from a very flat disk.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 05, 2016, 04:28:30 PM
Okay, thanks.  That's pretty much what I wanted to know about that part.  Go on...
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 05, 2016, 04:39:24 PM
What else would you like to know?

Also, I want to make sure we're on the same page. You mentioned occultation throughout, but if you're talking about detecting planets, astronomers tend to refer to that as the transit method. Occultation is usually mentioned in the context of a foreground object (something in the solar system) passing in front of a distant star. In that case, of course, planes don't really matter. Occultation can be used to discover objects in the solar system (asteroids and comets, for example) by directly blocking the light of another star or to learn about solar system objects we already know are there. For example, we can find the chemical composition of, say, a moon's atmosphere by seeing which wavelengths of light from an occulting star it blocks.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 05, 2016, 06:18:12 PM
Okay; I'm not disinterested in getting the slightly jargony bit right.  I'm interested in your reactions to anything I say on the subject, as your formal training is educational to me on a subject I find interesting, for all that I've never studied it seriously, just picked up in passing as much as any science fiction geek with a mind who reads should.

It seems increasingly plain, as our scant knowledge of our own solar system becomes slightly less pathetic, something that should have been more intuitive; very very faint gravitational influences really add up, given billions of years, thus things like orbital resonances being far more common than the pros seemed to assume when I was a kid - and of course, that's pretty much how we get prevailing planes of ecliptic, there being evidence that early system formation is a more than trivially chaotic event...  -Not that they didn't suspect a good deal of that as far back as Newton, but still found many a surprise around Saturn in 1980, observation always proving higher-rez than theory...  I'd opine that it wasn't the Newtonian/Einsteinian laws that were insufficiently worked out IRT space -I'm sure there's plenty the state of the art doesn't grok, but they seem to be at least a not-inadequate working approximation for many purposes- but the implications of timescales we're frankly incapable of intuiting.

-But then oort clouds must be too distant, and of insufficient average mass, for all that to work on our system's timescale of existence - certainly, any tendency for star systems lining up planes in a galaxy the age of ours would be almost solely due to any prevailing tendency of movement direction of galactic matter clouds at formation; if Pluto and the comets haven't lined up yet, in other words, an Alpha Centauri system needs a timescale difficult to even guess at by an order of magnitude or three.

Related in my mind, on the subject of deep time; when I came to understand how they thought bits of Mars could end up laying in Antarctica -no news story EVER, to my knowledge, said "meteor splash" for about ten years- I began to believe in the possibility of a sort of panspermia for the first time, w/o invoking Sargon's people (ST reference).  Given enough spores and time and a few energetic events, there's just no telling how far a single origin of life could spread, at least on an intra-galactic scale.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 05, 2016, 07:19:17 PM
One thing I'll mention is that solar systems being basically planar is primarily a result of the conservation of angular momentum, not gravitational influences. Here's a good way to think about this. Before the solar system formed, you had a molecular cloud sitting around, waiting to collapse under its own gravity (which would happen if it were perturbed by a supernova or a passing star, say). All of the particles in this cloud are basically moving around randomly, but you can think about their direction of movement relative to the center (where the star will be). If you then add up all of those random directions of movement, you'll find that the sum of those movements points in one particular direction. (This isn't special; it's just math. Add up a bunch of numbers and you get one number. Add up a bunch of directions and you get one direction.)

Once the cloud starts collapsing under its own gravity, conservation of angular momentum means the particles will all start spinning faster. They're still all moving randomly, but their average spin direction is the summed up direction from earlier. As the cloud collapses, more and more particles start running into each other, which tends to cancel out the random motions of the particles in the cloud. If all the random motions cancel out, you're left only with the average motion in one direction, which is some spinning orientation around the center where the star is. So you're left with a flat disc.

The reason something like the Oort Cloud isn't planar is either because (a) it wasn't really part of the initial collapse of the molecular cloud or (b) it consists of bodies that were chaotically thrown out of the solar system early on during formation.

As far as orbital resonances are concerned, there are two interesting discoveries that have been made as astronomy has matured. One is that resonances sometimes create gaps, but only on very long timescales. So, for example, there are gaps in the asteroid belt (the Kirkwood gaps) corresponding to resonances with Jupiter. Gravitational tugs over time mean that any asteroids at those distances get kicked out, but only over very long periods of time. So billions of years after Jupiter has settled into its current orbit, basically nothing remains there, but long ago there would have been asteroids present in unstable orbits.

The flip side of this is that some objects in resonances we currently see only exist because the configuration at present is relatively young, and eventually those bodies will get kicked out. That we see orbital resonances at all in the solar system actually suggests that the current orbits of planets and moons might be relatively recent (still speaking of tens or hundreds of millions of years). Astronomers are pretty confident that Jupiter and Saturn did a fair amount of migration early on, for example. But additionally, something like Saturn and its rings may be quite young, fragile, and short-lived on a solar system timescale.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 05, 2016, 07:51:31 PM
First half -not that I could have phrased it as well- pretty QED.

Second, largely just best informed assumptions available.  I've been watching the science of the nature and age and orbital mechanics of Saturn's rings, for instance, go back and forth longer than you've been alive.  Forgive my doubt until our observations are less pathetically incomplete...
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 06, 2016, 02:36:31 PM
I think there are legitimate reasons to be less skeptical of recent results in the study of the solar system. Over the course of your life, we've learned a tremendous amount about the planets and moons from probes and telescopes, and we've also seen significant advances in chaos theory, a mathematical tool for studying dynamical systems (such as the solar system).

Additionally, the people I've learned this stuff from are just as old as you, if not older. ;)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 06, 2016, 02:46:34 PM
-And actually know what they're talking about, sure. ;)

I still wish our observations were a lot closer to complete/satisfatory.  Thomas is my favorite disciple.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 06, 2016, 02:52:39 PM
It'll be awhile. Consider how much we don't know about the Earth, and then remember that the Earth is a dot as far as the solar system is concerned. We are definitely learning, but there is just so, so much to know.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 06, 2016, 03:17:21 PM
I wish there was more will to learn it...
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 06, 2016, 03:20:35 PM
Oh - and only slightly related -because everything is- but check the LHC story topped in general science if it's not old news to you about the new particles...
Title: Re: Astronomy/cosmology questions...
Post by: Valka on July 07, 2016, 10:59:31 PM
Lorizael, I've got a question related to the asteroid belt. There's a guy on CFC who is obsessed with convincing us that Babylonian mythology and Genesis are accurate descriptions of how the solar system and Earth were formed. He keeps insisting that Earth was formed in the asteroid belt because our water and Vesta's water are identical.

I can't find anything online anywhere that states even the possibility of Earth forming in the asteroid belt. Do you know of any theory or even a hypothesis by a reputable astronomer that talks about this?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 07, 2016, 11:50:40 PM
I believe I know what he's trying to talk about, but Lori will explain it a lot better and more accurately than I.

Protip: think oceans from comet water instead of Earth forming in the belt.
Title: Re: Astronomy/cosmology questions...
Post by: Valka on July 08, 2016, 12:38:33 AM
I believe I know what he's trying to talk about, but Lori will explain it a lot better and more accurately than I.

Protip: think oceans from comet water instead of Earth forming in the belt.
That's pretty much how I figured it, but he's absolutely not willing to listen to any views but his own, even those of real astronomers and astrophysicists.

I was willing to concede that I may have missed some hypothesis or theory about this, so thought I'd grab the opportunity here to ask someone who is into real science, not tabloid/mystical nonsense.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 08, 2016, 01:00:16 AM
Well the science has gone back and forth -and I hate to go into this much detail because Lori will, very correctly, correct me- in just the last few years on where all the water on this planet came from, judging from the (frequently bullcrap-ish, mostly through ineptitude) mainstream science articles I've seen.  It might be worth it to you to search, I dunno, "Comet water" in both the science subforums.  I'm trying to think of a good search term to turn up the at least one article that talks about a study that indicates the water molecules were just there with the rest of the matter cloud that Earth formed from, but --- "Earth's Water" maybe?  The search engine sucks, in true forum tradition, but a lot of those articles reference -even link; I always bother to do the link if there's one to a journal article- actual science and don't set off my bullcrap/the-writer-didn't-understand detector.

I believe the issue has more to do with steam being not-dense, the ice form being whitish/reflective, so either way, water molecules would tend not to stay around this distance from the sun in free orbits because light pressure - and the water form of water is a narrow temperature range unlikely to last long outside current earth conditions, not least in vacuum.  Science articles tend to frame it as molten early earth was too hot so it steamed off, but that's nonsense and bad reporting, surely...  Because it's steam it flies out of the atmosphere into space at escape velocity?  Surely more the same reason there's so much more ice and gas in the outer system than inner, which they tend to assume was light pressure pushing away the lighter atoms in the primordial cloud faster than the heaver ones. - and moreso close in where the light's spread out less.

Lori will still be more help...
Title: Re: Astronomy/cosmology questions...
Post by: Valka on July 08, 2016, 01:16:47 AM
Of course - it's been over 20 years since I last took any formal astronomy courses, and while I've tried to keep up, too many of those 20 years were spent in a mental fog because I was really sick, housebound, and unable to concentrate on much of anything. So I've missed a lot.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 08, 2016, 01:56:34 AM
I wish I recalled more about what the Dawn probe found at Vesta -but that never got as much coverage as it rates, not unlike Ceres now, and I'm not sure it's still there, it gets so little attention...

Vesta, IIRC, is indeed pretty icy - but they've been fairly confident about that for a very long time; high albedo and I don't know what-all.  The last I recall about Ceres, they were thinking the shiny spots were more like crysaline salt buildups left behind from ice sublimation in vacuum or something of the sort...
Title: Re: Astronomy/cosmology questions...
Post by: Valka on July 08, 2016, 03:26:58 AM
Should be interesting to see just how dated Ben Bova's Asteroid Wars series becomes when they find out more about Ceres. A significant amount of the action in those novels take place in a mining outpost in Ceres (they live underground) and in orbit.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 08, 2016, 03:34:19 AM
[shrugs]  Larry Niven likes to girldog that his first published story The Coldest Place, was rendered obsolete about a week before the magazine it appeared in hit the stands - the point of the tale hinges on Mercury being orbitally locked, and it was 1964 and Mariner happened...
Title: Re: Astronomy/cosmology questions...
Post by: Valka on July 08, 2016, 03:53:02 AM
Progress happens.  :D

Pretty much everything Heinlein and Bradbury have written about places in the Solar System became dated decades ago. And every time I hear someone talking about some "Rigel colony" or civilization on a planet orbiting Vega, I'm just taken right out of the story because what we know now means those colonies are impossible.

I realize that we can't hold writers from 50-80 years ago responsible for not knowing what new knowledge would come along; they worked with what they knew at the time, but it does take a mental toggleswitch to enjoy the stories now (at least for me).
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 08, 2016, 04:07:23 AM
Bradbury doesn't count - his stuff is Norman Rockwell fantasy, not SF, with spaceships and/or the boogerman, never had anything to do for a second with the scientific state of the art, ever.  I don't get the appeal of Bradbury, for that matter.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 08, 2016, 02:03:24 PM
Lorizael, I've got a question related to the asteroid belt. There's a guy on CFC who is obsessed with convincing us that Babylonian mythology and Genesis are accurate descriptions of how the solar system and Earth were formed. He keeps insisting that Earth was formed in the asteroid belt because our water and Vesta's water are identical.

I can't find anything online anywhere that states even the possibility of Earth forming in the asteroid belt. Do you know of any theory or even a hypothesis by a reputable astronomer that talks about this?

The current best model for how the planets got to where they are is the Nice model (https://en.wikipedia.org/wiki/Nice_model), according to which the inner planets haven't really moved much at all. The best theory we have for why the asteroid belt is the way it is is that Jupiter (which astronomers think migrated inward and then back out at one point) prevented planetesimals from accreting into full-size planets because its gravity made things a little too exciting. Accreting requires relatively low velocity impacts. Too high a velocity and little planets just shatter instead.

Eventually, all the little planetesimals in what is now the asteroid belt were gobbled up or ejected, leaving behind what is in reality a very sparsely populated region. (The total mass of the asteroids is a tiny fraction of our moon, for example.) So from that it doesn't seem plausible that Earth formed in the asteroid belt, because it would have been subject to the same harsh gravitational influences, and a peaceful migration inward in response is way, way less likely than being destroyed or kicked out of the solar system entirely.

Additionally, much to Pluto's chagrin, the modern definition of a planet requires "clearing out" your orbit. This process isn't expected to take very long, only something in the range of tens of millions of years. If Earth had been inside the asteroid belt long enough to fully form before migrating inward, why didn't it clear out the asteroid belt?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 08, 2016, 02:43:19 PM
...I wonder how the Theia impact may have informed all that.  It had to be a somewhat low-energy event as two planets colliding goes, but it can't have not affected the orbit...


I left out something about that paper last year that posited the water was just there all along - 1.) It's not that much water in the first place, proportionately, and 2.) there was much about evidence/calculations the researcher(s) claimed to have found that the tendency of water in all its states to bond with and/or plate on the surface of denser particles tends to account for the proportions found on Earth's surface even with light pressure in the primordial cloud, so no icy late bombardment need apply.

It is the nature of how science works -slowly, sometimes, as a community- that this has not taken over the dominant thinking, as far as I know, and no idea if other solar system formation scientists aware of it find it to have merit.  There's certainly still references to Earth's comet water coming up in popular reporting still, very notably the Rosetta team mentioning it, not that they wouldn't be a bit married to it by the nature of what they were researching...
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 08, 2016, 03:58:07 PM
...I wonder how the Theia impact may have informed all that.  It had to be a somewhat low-energy event as two planets colliding goes, but it can't have not affected the orbit...

Really all depends. Currently, thinking is that Theia was about Mars-sized, having ~1/10 the mass of the Earth. So you have a relatively slow collision between the Earth and a much lighter object. Momentum gets transferred, but the change in momentum might not have been very large. That's because the Earth has a lot of momentum, both from its orbit around the Sun and its own spinning. If some of the momentum goes into changing the Earth's orbit, and some into changing it spin (which depends on how off-center the impact was), then maybe the orbit doesn't get changed much at all.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 08, 2016, 06:03:11 PM
It had to have ended in a pretty fast spin by our current standards, with the nascent molten moon freaky close -which must have been a SIGHT, not that there would a place to stand nor weather for good seeing- and tidal drag effects and all and over four billion years dragging to make a 24 hour period.

-ISTR something on the Discovery channel claiming 15 hours, but cable documentary channels are pretty much the National Enquirer of science these days, and I know not to have enormous respect for that figure...
Title: Re: Astronomy/cosmology questions...
Post by: Valka on July 08, 2016, 08:13:45 PM
Lorizael, I've got a question related to the asteroid belt. There's a guy on CFC who is obsessed with convincing us that Babylonian mythology and Genesis are accurate descriptions of how the solar system and Earth were formed. He keeps insisting that Earth was formed in the asteroid belt because our water and Vesta's water are identical.

I can't find anything online anywhere that states even the possibility of Earth forming in the asteroid belt. Do you know of any theory or even a hypothesis by a reputable astronomer that talks about this?

The current best model for how the planets got to where they are is the Nice model (https://en.wikipedia.org/wiki/Nice_model), according to which the inner planets haven't really moved much at all. The best theory we have for why the asteroid belt is the way it is is that Jupiter (which astronomers think migrated inward and then back out at one point) prevented planetesimals from accreting into full-size planets because its gravity made things a little too exciting. Accreting requires relatively low velocity impacts. Too high a velocity and little planets just shatter instead.

Eventually, all the little planetesimals in what is now the asteroid belt were gobbled up or ejected, leaving behind what is in reality a very sparsely populated region. (The total mass of the asteroids is a tiny fraction of our moon, for example.) So from that it doesn't seem plausible that Earth formed in the asteroid belt, because it would have been subject to the same harsh gravitational influences, and a peaceful migration inward in response is way, way less likely than being destroyed or kicked out of the solar system entirely.

Additionally, much to Pluto's chagrin, the modern definition of a planet requires "clearing out" your orbit. This process isn't expected to take very long, only something in the range of tens of millions of years. If Earth had been inside the asteroid belt long enough to fully form before migrating inward, why didn't it clear out the asteroid belt?

THANK YOU!!! :D

Would it be permissible to post a link to this post over at CFC? In any case, I will post the link you provided to the Nice model.

(and it's nice - no pun intended - to see references to the Oort Cloud; this guy thinks it's not real and accuses me of "believing" in it as though it's some kind of religious thing or fairy tale, even though I've posted links about it)
Title: Re: Astronomy/cosmology questions...
Post by: E_T on July 08, 2016, 08:40:58 PM
One method that I can think of that helped to shape the planetary rotational planes would be tidal forces and effects on orbiting debris that are in the process of stellar and planetary formations...
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 09, 2016, 01:02:10 AM
Lorizael, I've got a question related to the asteroid belt. There's a guy on CFC who is obsessed with convincing us that Babylonian mythology and Genesis are accurate descriptions of how the solar system and Earth were formed. He keeps insisting that Earth was formed in the asteroid belt because our water and Vesta's water are identical.

I can't find anything online anywhere that states even the possibility of Earth forming in the asteroid belt. Do you know of any theory or even a hypothesis by a reputable astronomer that talks about this?

The current best model for how the planets got to where they are is the Nice model (https://en.wikipedia.org/wiki/Nice_model), according to which the inner planets haven't really moved much at all. The best theory we have for why the asteroid belt is the way it is is that Jupiter (which astronomers think migrated inward and then back out at one point) prevented planetesimals from accreting into full-size planets because its gravity made things a little too exciting. Accreting requires relatively low velocity impacts. Too high a velocity and little planets just shatter instead.

Eventually, all the little planetesimals in what is now the asteroid belt were gobbled up or ejected, leaving behind what is in reality a very sparsely populated region. (The total mass of the asteroids is a tiny fraction of our moon, for example.) So from that it doesn't seem plausible that Earth formed in the asteroid belt, because it would have been subject to the same harsh gravitational influences, and a peaceful migration inward in response is way, way less likely than being destroyed or kicked out of the solar system entirely.

Additionally, much to Pluto's chagrin, the modern definition of a planet requires "clearing out" your orbit. This process isn't expected to take very long, only something in the range of tens of millions of years. If Earth had been inside the asteroid belt long enough to fully form before migrating inward, why didn't it clear out the asteroid belt?

THANK YOU!!! :D

Would it be permissible to post a link to this post over at CFC? In any case, I will post the link you provided to the Nice model.

(and it's nice - no pun intended - to see references to the Oort Cloud; this guy thinks it's not real and accuses me of "believing" in it as though it's some kind of religious thing or fairy tale, even though I've posted links about it)

Sure, you can link to it. I should note that we haven't seen the Oort Cloud, but we have every reason to believe it exists based on (a) the nebular hypothesis and (b) the frequency and trajectories of long period comets. Jan Oort's original paper from 1950 about his eponymous cloud is a great read, btw.
Title: Re: Astronomy/cosmology questions...
Post by: Valka on July 09, 2016, 01:37:34 AM
Thank you, Lorizael. It's nice to hear reason instead of "but it can't exist, because it it did, we should see comets every night and we don't."

Well, maybe because when you consider the average human life span and the incredibly long orbits of some of these comets... it'll be thousands of years before Hale-Bopp or Hyakutake come this way again, so I consider myself extremely fortunate to have seen them with my own eyes.

Actually, I started writing a filk about comets, 20-odd years ago. Never finished it, though. I got bogged down in the last verse and still haven't figured out the last two lines.
Title: Re: Astronomy/cosmology questions...
Post by: Valka on July 16, 2016, 04:03:56 AM
*puts on Moderator's hat for a moment*

I've done a little housekeeping in this thread, and ask that we please stick to the topic. Lorizael has been generously sharing his knowledge with the forum, and it's disrespectful to him and everyone else who is interested in a serious discussion of astronomy/cosmology to go off-topic. Thank you.

*removes Moderator's hat*
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 22, 2016, 09:05:33 PM
Looming large, dark matter still proves hard to pin down (http://alphacentauri2.info/index.php?topic=18109.0)

OohoohOOH!  Mistah Kotter!  I know the answer to this one!
Title: Re: Astronomy/cosmology questions...
Post by: Valka on July 22, 2016, 11:07:14 PM
Well, I finally got around to mentioning this thread in that silly discussion over at CFC. Berzerker hasn't replied to my post yet about the issue of Earth not being formed in the asteroid belt.

Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 22, 2016, 11:41:12 PM
Oh - it was Berz?  Big shrill strident Libertarian, right?
Title: Re: Astronomy/cosmology questions...
Post by: Valka on July 23, 2016, 12:30:01 AM
Yeah. This is certainly not the first time a thread like this has come along, and it's just mentally painful to read most of it.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 23, 2016, 01:19:51 AM
I would not be optimistic about the odds of changing Berz's mind, btw.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 23, 2016, 01:24:29 AM
;lol  Yeah.  I know of Berz from the Pit, where he's honestly not one of the bad ones IMAO - but he's tres' hardcore on the Libertarian stuff and quite convicted.  Like, I really mean hardcore, but that still tends to leave him almost a sane voice in some of the 'Poly political argument slap-fight threads.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 26, 2016, 01:51:13 AM
Astronomers May Have Spotted a Direct Collapse Black Hole
http://alphacentauri2.info/index.php?topic=18117.0 (http://alphacentauri2.info/index.php?topic=18117.0)

This struck me as sounding suspiciously like the reporter may not have understood what he was talking about.  So?  Does the article make sense?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 26, 2016, 02:17:46 AM
What seems nonsensical about it?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 26, 2016, 02:29:48 AM
...[furrows brow] I thought black holes of all sizes were supposed to have come out of local fluctuations in the big bang, for one thing.  When did that go away?  Are you telling me that explanation made sense?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 26, 2016, 03:14:20 AM
There's not a lot of good observational evidence for primordial black holes, and you would expect there to be very few large primordial black holes if they exist at all. For black holes that are stellar mass and above, the prevailing theory is that they're the end stage of massive stars post-supernova. But because space is big (and some other problems), assembling stellar mass black holes into supermassive black holes is thought to be a tricky thing; yet we see supermassive black holes very early on in cosmic history, suggesting quite rapid assembly.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on July 26, 2016, 03:41:08 AM
I don't know why, given, say, an Earth-mass primordial starting out, you could rule out the thing feeding way up, to understate it, with all the mass in the universe still squeezed into say, a 10 light-year sphere at an early point...
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 26, 2016, 04:16:02 AM
It's difficult to have an intuition about the early universe because all evidence indicates it was nothing at all like what we see today. The only way to get a handle on it is with a bit of math, so let me demonstrate just with the numbers you provided.

In cosmology, the size of the universe is inversely proportional to its temperature. So with a 10 light-year universe, which is less than a billionth its current size, the temperature would have been something like a billion or 10 billion kelvins. At that temperature, nothing sticks together. Particles (no atoms yet) that collide will annihilate rather than bond. What's more, the universe is at roughly that size for a fraction of a second, because it's expanding incredibly quickly at this stage. So there's simply too little time for any appreciable accretion to occur. The result is that the universe is very smooth for a long, long time.

We know this based on the cosmic microwave background. The CMB has an extremely uniform temperature of almost exactly 2.725 K everywhere we look. That uniform temperature corresponds to uniform density in the early universe. The differences you see in the CMB map are 1 part in 10,000. The big density fluctuations we see today (planets, stars, galaxies, voids, etc.) all came about much later as the very minor early density fluctuations started clumping.
Title: Re: Astronomy/cosmology questions...
Post by: Spacy on July 26, 2016, 04:23:19 AM
The only thing faster than the speed of light (that we know of) is Nothing.

Note: nothing is something, but it is still nothing.

Big bang 102.  Big bang 101 is that it is really poorly named - would be better to call it the "everywhere stretch" (stole that one from minutephysics guys). 
Title: Re: Astronomy/cosmology questions...
Post by: E_T on July 30, 2016, 11:23:56 PM
According to some conjectures, the matter/energy total amount is "finite", IF and only if, there is an "edge" to the universe.  But if the universe is without bounds, then that balance is infinite...
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on August 08, 2016, 04:31:29 PM
How bright are the Perseids? At times, I've been tempted to fetch a book at night to see if I could read it from the light pollution and the local paper says to avoid porchlights, streetlights, and such. Assuming it's not cloudy.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 08, 2016, 04:57:03 PM
They vary in brightness depending on how big the meteor is (so brighter ones will be less common than fainter ones), but the brightest meteors will outshine planets. The faintest ones will be dimmer than the most easily visible stars, so you do want to get out somewhere dark to see them. That is, they're talking about this year possibly being particularly strong, with as many as 200 meteors/hour, so you could expect to see a few every minute, but only if you're in an area dark enough to catch them all.
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on August 08, 2016, 05:07:31 PM
So, like, halfway to Winchester?

Edit: http://www.lightpollutionmap.info/#zoom=9&lat=4706023&lon=-8568392&layers=B0TFFFF (http://www.lightpollutionmap.info/#zoom=9&lat=4706023&lon=-8568392&layers=B0TFFFF)

Double edit: WaPo has an article with suggestions, one of which is western Loudoun county, so yes, halfway to Winchester. Merely rates as "Decent". I don't feel like a trip to Shenandoah either.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on August 16, 2016, 03:31:09 PM
Have Scientists Discovered The Fifth Force Of Nature? (http://alphacentauri2.info/index.php?topic=18182.msg99544#msg99544)
 
Journal link in the article...
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on August 16, 2016, 03:48:43 PM
‘Largest structure in the universe’ undermines fundamental cosmic principles (http://alphacentauri2.info/index.php?topic=18183.msg99546#msg99546)
Title: Re: Astronomy/cosmology questions...
Post by: E_T on August 16, 2016, 05:39:55 PM
Did you see the post at WPC, that Arnie put up, about the disccovery of an Earthlike, Goldielocks Zone, Exoplanet around Proxima Centauri (which is ~0.12 ly closer to us than Alpha Centauri)??
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on August 16, 2016, 09:15:12 PM
I've seen it - and the one gwilly put up two weeks ago.  -Proxima isn't a discreet star though, IIRC; it a name for the system of three...
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 17, 2016, 06:15:27 AM
It's the other way around. Alpha Centauri is the name of the binary star system (with stars A and B), and Proxima Centauri was discovered much later as an orbiting third.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on August 17, 2016, 03:48:47 PM
Is it still going to be closer in 100 years, then?
 
 
The edge of the universe is closer than scientists previously thought (http://alphacentauri2.info/index.php?topic=18189.0)
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 18, 2016, 02:50:05 AM
It's currently moving toward us, but I only know that because I looked it up on wikipedia.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on August 18, 2016, 02:53:34 AM
Did the Wikipedia say what the period was?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 18, 2016, 03:19:26 AM
Best guess is its orbital period around Alpha Centauri is something like half a million years. It will be approaching us for another 27,000 years or so. (I trust Wikipedia for this kind of information because I know what astrophysical databases they're pulling their numbers from.)
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on August 30, 2016, 07:43:53 PM
IRAS 19312+1950 (http://www.jpl.nasa.gov/news/news.php?feature=6607), why?
Title: Re: Astronomy/cosmology questions...
Post by: gwillybj on August 30, 2016, 09:06:27 PM
hmmm...
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 31, 2016, 01:55:28 AM
IRAS 19312+1950 ([url]http://www.jpl.nasa.gov/news/news.php?feature=6607[/url]), why?


Stellar models are fiendishly complicated and not something I've studied in depth. The one thing I'll say, which the article talks about, it that the more distant a star is, the more difficult it is to tell if you're seeing the star or the star+interstellar medium of gas and dust in between. Disentangling the two often involves looking at a star in multiple EM bands (radio, optical, IR) and seeing what gets through.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on August 31, 2016, 03:05:44 AM
IRAS 19312+1950 ([url]http://www.jpl.nasa.gov/news/news.php?feature=6607[/url]), why?


Stellar models are fiendishly complicated and not something I've studied in depth. The one thing I'll say, which the article talks about, it that the more distant a star is, the more difficult it is to tell if you're seeing the star or the star+interstellar medium of gas and dust in between. Disentangling the two often involves looking at a star in multiple EM bands (radio, optical, IR) and seeing what gets through.


Unlike the black and anti stuff in the Universe, this makes a lot of sense to me.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 31, 2016, 05:44:16 AM
Unlike the black and anti stuff in the Universe, this makes a lot of sense to me.


Assuming you mean dark when you say black, I've recently been thinking about a new way to talk about dark matter. Pretend you're a theoretical physicist and you'd like to win a Nobel Prize for discovering a new kind of matter. So you sit down and come up with the completely bonkers idea of matter that interacts only via gravity (but not electromagnetism or any other force). You call this hypothetical stuff gravimatter.

To win your Nobel Prize, you're gonna have to get some experimental/observational scientists to detect it by some means. So how do you test for the presence of gravimatter? Well, you look for regions where there's a lot of gravitational interaction. Unfortunately, because normal matter also interacts via gravity, you can't easily disentangle gravimatter from regular matter. The best way to do so is to play on the key difference between your hypothesized gravimatter and regular matter, which is that regular matter interacts via electromagnetism but gravimatter doesn't.

Because regular matter responds to electromagnetism, collisions convert motion (kinetic energy) into light (thermal energy), which means we can tear gravimatter away from regular matter by looking at regions that are moving very quickly. That is, we can do like the particle physicists do and slam stuff together. When you slam stuff together, the regular matter will slow down and start to glow, but the gravimatter will just keep going. That way, if you detect gravitational interaction where there's no glowing, you can be sure you're looking at gravimatter and not regular matter.

Gravity is weak, though, so you can't really do this in a particle accelerator and expect to find anything. Instead you ask astronomers to look through the universe for cases where this might be happening. The astronomers point their telescopes into space and find this, the Bullet Cluster.

(http://www.physicscentral.com/explore/action/images/bullet-cluster.jpg)

The Bullet Cluster is a collision between two galaxy clusters. The pink-ish red stuff in the middle are x-rays from gas heated by the two clusters ramming into each other. The x-rays emissions are  stuck in the middle where the gas has been slowed down by the massive collision. The blue stuff on the outside, moving away from the center, represents gravitational lensing, which is the degree to which matter gravitationally distorts the image of background objects. There's no red glow where the blue lensing is happening (the colors are totally arbitrary, btw), because there's virtually no regular matter there. The best explanation for why you have lensing without regular matter is gravimatter.

By the strength of the lensing, you can estimate how much of the galaxy cluster is composed of gravimatter. If you guess that this is a typical amount of gravimatter, then you can also predict that gravimatter will probably play a very significant role in the structure of the universe, dictating things like how the galaxy web will form, what sorts of fluctuations you'll see in the CMB, and what kind of rotation curves spiral galaxies will have. And sure enough, gravimatter seems to pop up in all of those places (and more) in the proportions dictated by the Bullet Cluster and similar regions. Congratulations, the Nobel Committee should be along shortly.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on August 31, 2016, 07:53:19 AM
So gravey matter is concentrated in the mash?  ;)

You're pretty good at this! I really hope you find a niche as an author or virtual university professor or planetarium director or something where you can find a broad audience.

Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 31, 2016, 01:34:01 PM
So gravey matter is concentrated in the mash?  ;)

 ;b; ;lol

Quote
You're pretty good at this! I really hope you find a niche as an author or virtual university professor or planetarium director or something where you can find a broad audience.

Well, I did just start TAing for an introductory astronomy course. We'll see how that goes.
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on September 08, 2016, 07:40:11 PM
Stellar models are fiendishly complicated and not something I've studied in depth.

Does that mean I can't ask about Yellow Hypergiants?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on September 09, 2016, 02:53:38 AM
You can certainly ask. I might even know something.
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on September 09, 2016, 06:20:12 PM
Part the first: correct or incorrect?
Yellow Hypergiants are theorized to be either post-Red Supergiant of moderate instability evolving blueward one or more times, or relatively more stable stars evolving towards Red Supergiant for the first time. And where the stars of the former type are losing mass [due to various reasons I'm not interested in trying to re-learn/remember right now].
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on September 10, 2016, 11:14:10 PM
Correct, although you can get that part just from wiki.
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on September 11, 2016, 05:31:50 AM
Sometimes wiki is too hard.

But what do the post-Red Supergiants stars become? Luminous blue variables? Supernovae? Other?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on September 11, 2016, 02:37:44 PM
That is a relatively easy question to answer, as the ultimate fate of a star is almost completely determined by its initial mass. Small stars blow off their outer layers and become white dwarfs; large stars explode as supernovae, leaving either a neutron star or black hole behind. Yellow hypergiants are initially massive, so they go the supernova->neutron star/black hole route.

(Before supernova, there is some variety of slightly unpredictable evolution through red supergiant and luminous blue variable and the like, all of which represent the star fighting a losing battle against gravity by finding more things to burn. When the battle is lost and outward pressure cannot match inward pressure from gravity: boom.)

Everything else is just a stage in the process of stellar evolution (yellow hypergiant, Cepheid variable, T Tauri star, etc.), whether that stage is long or short. If it's a short stage (or a stage not all stars go through for whatever reason), then we are unlikely to see many stars in that stage. This is why yellow hypergiants are observationally rare; they don't spend much time in the wacky yellow hypergiant phase. But they are (probably) not intrinsically different from any other star of the same initial mass (except in details).

Figuring out what all those stages are is hard, but linking the beginning and the end stages is relatively easy.
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on September 11, 2016, 09:34:30 PM
It's the intervening stages that are interesting.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on September 12, 2016, 03:14:12 AM
Indeed, but very complicated. It's easy-ish to say what can happen but much harder to say what will happen. For example, there's a famous 60 year old paper in astrophysics known as B2FH (https://en.wikipedia.org/wiki/B2FH_paperl) that describes in detail the process of stellar nucleosynthesis all the way up to iron. You can accurately model how all that will happen in a star without actually having precise models for the evolution of stars, despite the fact that some of those weird evolutionary stages are necessary to produce some of those elements.
Title: Re: Astronomy/cosmology questions...
Post by: E_T on September 12, 2016, 05:12:53 AM
what is required is detailed observation over very long periods of time...
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on November 13, 2016, 07:25:00 PM
(http://imgs.xkcd.com/comics/astrophysics.png)
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on November 14, 2016, 04:23:44 AM
Taking cosmology this semester, so I've seen the equations of MOND (Modified Newtonian Dynamics, the main dark matter alternative). They work well for that one thing dark matter was originally proposed to explain (galaxy rotation curves) but not anything else where dark matter seems to be having an effect.

For example, right now we're working through the formation of large scale structure in the early universe. If the early universe is composed only of regular matter, then it acts basically like a fluid. That is, it has pressure and doesn't want to be compressed (by gravity), which slows the formation of structure. If the universe is mostly dark matter, however, then matter collapses without any impeding force and structures do form (when we observe them to form).
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on November 14, 2016, 04:46:33 AM
Taking cosmology this semester, so I've seen the equations of MOND (Modified Newtonian Dynamics, the main dark matter alternative). They work well for that one thing dark matter was originally proposed to explain (galaxy rotation curves) but not anything else where dark matter seems to be having an effect.

For example, right now we're working through the formation of large scale structure in the early universe. If the early universe is composed only of regular matter, then it acts basically like a fluid. That is, it has pressure and doesn't want to be compressed (by gravity), which slows the formation of structure. If the universe is mostly dark matter, however, then matter collapses without any impeding force and structures do form (when we observe them to form).

SO...by turning to the Dark Side the Universe could unleash the power of The Force. ;-)

How goes the teaching part?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on November 14, 2016, 05:54:05 AM
SO...by turning to the Dark Side the Universe could unleash the power of The Force. ;-)

Current models of dark matter say that (a) it's everywhere, (b) it can pass right through us, and (c) galaxies wouldn't exist without it. So then you could say it surrounds us, it penetrates us, it binds the galaxy together...

Quote
How goes the teaching part?

I'm enjoying it. Grading is a hassle and kind of nerve-wracking. But getting up in front of a class and breaking down complex topics and answering questions and trying to share a little bit of what I'm passionate about... it's stimulating and fun.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on November 14, 2016, 06:36:11 PM
SO...by turning to the Dark Side the Universe could unleash the power of The Force. ;-)

Current models of dark matter say that (a) it's everywhere, (b) it can pass right through us, and (c) galaxies wouldn't exist without it. So then you could say it surrounds us, it penetrates us, it binds the galaxy together...

Quote
How goes the teaching part?

I'm enjoying it. Grading is a hassle and kind of nerve-wracking. But getting up in front of a class and breaking down complex topics and answering questions and trying to share a little bit of what I'm passionate about... it's stimulating and fun.

 I'm delighted to hear that you're hitting your stride. Besides, explaining is  good practice for when you write a book.
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on November 14, 2016, 08:36:04 PM
Quote
How goes the teaching part?

I'm enjoying it. Grading is a hassle and kind of nerve-wracking. But getting up in front of a class and breaking down complex topics and answering questions and trying to share a little bit of what I'm passionate about... it's stimulating and fun.

How long before we can watch you on TV and learn about space/get beguiled into your cult?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on November 14, 2016, 10:37:04 PM
Ooh! Ooh! OOH!  Can I join your evil science cult Mister Vandewalle?

Can I, can I, huh huh huh?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on November 15, 2016, 04:12:28 AM
How long did it take Bill Nye to become Bill Nye the Science Guy after he got his degree?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on November 15, 2016, 04:22:13 AM
...He spent quite a few years as a professional sketch comedian first...
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on November 15, 2016, 05:04:31 AM
Well, is there something Lori should watch, or a drama  course he should audit or something?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on November 15, 2016, 01:41:59 PM
Time as an improv comedian wouldn't be the worse possible prep, actually.
Title: Re: Astronomy/cosmology questions...
Post by: Spacy on November 15, 2016, 10:05:38 PM
And, get on your local PBS / Talk Radio show as well, to get that "show biz" start and see how they really work (particularly behind the scenes).  I cannot imagine it would be super easy. 
Title: Re: Astronomy/cosmology questions...
Post by: Rextraos on November 16, 2016, 05:27:40 AM
This thread is pretty cool, right up my alley. However, don't you think it's kind of a dark matter to talk about? *snicker*
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on December 20, 2016, 03:19:01 PM
Gamma-ray background yields no evidence of dark matter (http://alphacentauri2.info/index.php?topic=18494.msg102749#msg102749)
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on December 20, 2016, 06:19:50 PM
So the thing about dark matter is... we don't really have a good handle on how to detect it by non-gravitational means. Astrophysicists are essentially hoping that dark matter is something like the rest of the particles known, which means they have to pop into existence due to fluctuations in some quantum field, and the leading candidate is that weak interactions are involved, because if it were anything else, we definitely would have seen dark matter by now. So the continuing failure of these searches means it's harder to get dark matter out of standard particle physics, but the failures don't in any way negate the evidence from gravity. (And as I've gone over before, much of the gravitational evidence cannot be accounted for by modifications to how gravity works.)
Title: Re: Astronomy/cosmology questions...
Post by: E_T on December 21, 2016, 07:24:46 AM
How does dark matter fit into the string theories?  I think is something fundamental that is under our noses...
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on December 22, 2016, 05:03:18 AM
Is The Universe is held together with string OR is The Universe held together by The Force? ( Yeah, I know that's not what ET said, I'm just going off on a tangent as per usual )

My usual reaction to a question like this is "Why does it have to be so binary?" Couldn't it be both? Sometimes people say one is lying and one is telling the truth. Not necessarily. Maybe they simply have different perspectives, like the blind men and the elephant parable. OR maybe they're both wrong, or both being deceptive, in whole or in part. 

Well, I guess I'm being more philosophical than scientific. Fortunately for us, our resident thread expert is knowledgeable of both disciplines.
Title: Re: Astronomy/cosmology questions...
Post by: E_T on December 23, 2016, 12:06:53 AM
String Cheese!!
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on December 27, 2016, 05:30:12 PM
The Case Against Dark Matter (http://alphacentauri2.info/index.php?topic=18521.msg102866#msg102866)

...I can't say I entirely understood this...
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on December 30, 2016, 08:11:41 PM
Suppose Dark Matter is simply the gravitational shadow of particles moving at the speed of light. You can't detect them by other means because they no longer exist in that time and place.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on December 31, 2016, 05:12:03 AM
Sorry for not participating in this thread lately. Brain has been mush recently. But in terms of dark matter being speed of light particles, that's probably not the case. In general relativity, gravity comes not from mass but from the stress-energy tensor at every point in space. For situations we're familiar with, the main contribution to the stress-energy tensor is mass. But as the name suggests, energy plays into it as well. So photons and other massless, speed-of-light particles--which do possess energy--already contribute to gravity in a known, quantifiable way. And we know how many photons are out there in the universe (roughly) based on things like the temperature of the cosmic microwave background.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on January 13, 2017, 04:41:16 PM
We Still Don't Know How Fast The Universe Is Expanding (http://alphacentauri2.info/index.php?topic=18614.msg103166#msg103166)
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on January 13, 2017, 05:27:32 PM
Suppose Dark Matter is simply the gravitational shadow of particles moving at the speed of light. You can't detect them by other means because they no longer exist in that time and place.

So much for that improvised theory. Lucky for us that the universe had a cosmic microwave to make the primordial soup.

I hope you get the rest or relaxation you need to get your brain back to normal, Lori. I enjoy and appreciate your explanations in this thread, and your general presence on this board. Thanks!
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on January 14, 2017, 09:07:10 PM
https://www.washingtonpost.com/news/speaking-of-science/wp/2017/01/10/study-suggests-earth-once-had-many-moonlets-until-they-merged-to-form-the-moon/?postshare=6681484155959173&tid=ss_tw&utm_term=.4c1f985bfdd6 (https://www.washingtonpost.com/news/speaking-of-science/wp/2017/01/10/study-suggests-earth-once-had-many-moonlets-until-they-merged-to-form-the-moon/?postshare=6681484155959173&tid=ss_tw&utm_term=.4c1f985bfdd6)

When I was a kid the Big Bang theory wasn't in vogue. It was the least popular. Simplistic catastrophic one-time event explanations seemed to be too easy to explain The Cosmos. The Original Universe spun so fast that it slung stars spiraling out of the galaxies....Or a gas and debris field gradually condensed into a Universe...or something. Then they found the background noise from the Big Bang and the rest is history.

Traditional thinking had the Moon knocked loose from the Pacific Ocean basin or sprung fully formed from the head of Zeus.  Catastrophic. Well, no chemical evidence of the theoretical Theia, so maybe we're leaning towards fully formed, but how did it Earth shake off a seventh of it's mass and the two pieces not veer in different directions?

I'm fuzzy on the amalgamated moonlets theory, though. Did this happen when the rock was molten, like drops of mercury gently consolidating themselves into a blob? Or did gravity, mass and velocity crush the moonlets into a sphere, the way we might make a snowball from chunky/granular snow?  I guess that's the part of the theory they're working on.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on January 27, 2017, 03:38:32 PM
New findings confirm cosmos expanding at faster rate than previously thought (http://alphacentauri2.info/index.php?topic=18702.msg103514#msg103514)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on January 31, 2017, 03:28:08 PM
Hints Of Charge-Parity Violation Detected In Baryons (http://alphacentauri2.info/index.php?topic=18730.0)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on February 11, 2017, 05:20:43 PM
Why Science Will Never Know Everything About Our Universe (http://alphacentauri2.info/index.php?topic=18817.msg103794#msg103794)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on March 18, 2017, 03:21:22 PM
Giant ring of galaxies scattered during Andromeda flyby challenges Einstein's theory of gravity (http://alphacentauri2.info/index.php?topic=19034.msg104411#msg104411)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on March 24, 2017, 02:25:58 PM
ALMA Reveals Gigantic Halos Around Ancient Galaxies (http://alphacentauri2.info/index.php?topic=19080.0)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on March 31, 2017, 08:35:22 PM
Is Dark Energy Real? Simulation Suggests Gravity Is Enough To Explain Universe's Accelerated Expansion (http://alphacentauri2.info/index.php?topic=19133.0)
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on April 07, 2017, 12:19:44 AM
NBC news anchor Lester Holt just showed me a beautiful picture of Jupiter taken by the Hubel, and told me that Jupiter is at it's closest to Earth, only 450 miles.

We replayed it twice. 450 miles!

If it passed that close, wouldn't we lose our Moon, atmosphere, and oceans? Wouldn't that alter our orbit, too?
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on April 07, 2017, 12:22:53 AM
For that matter, would people and stuff "fall"/float/levitate to Jupiter, too?
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on April 07, 2017, 12:26:07 AM
Or would Jupiter boil and explode as it approached the Sun before it even got that close to us?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on April 07, 2017, 12:35:21 AM
We'd fry from the radiation.  That would put Earth inside Jupiter's huge Van Allen belts, and they are INTENSE.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on April 07, 2017, 04:34:16 AM
We'd fry from the radiation.  That would put Earth inside Jupiter's huge Van Allen belts, and they are INTENSE.

I didn't even realize they had them.... but it makes sense, now that you mention it.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on April 07, 2017, 02:17:51 PM
So if Jupiter were magically transported such that its surface were 450 miles away from our surface and somehow kept there, then yes, life on Earth would be unpleasant. At that distance, Jupiter's tidal forces would start to tear the Earth apart, although Earth is very dense, which makes it more survivable. Jupiter's radiation would also be a problem--it is for the satellites we send there, which have to be very careful during close flybys--but Earth's magnetosphere would also offer protection. So the two planet's magnetospheres would interact, and the result would be... complicated... but my guess is probably bad for the residents of Earth given how radiation-blasted Io is.

If Jupiter passed by us and reached a closest approach of 450 miles, it's more difficult to say what would happen because that all depends on the specifics of its trajectory. The faster Jupiter moves as it passes is, the less effect it has, because you can kind of approximate its effect on our orbit by adding up the cumulative effect of Jupiter at each moment in time. So the less time it spends around us, the smaller the effect. Still, at 450 miles, that's well inside the orbit of the moon, so it would probably screw up both our orbit and the moon's.

Jupiter itself should survive being that close to the sun. It certainly wouldn't explode. Think about all the hot Jupiter exoplanets we've discovered. For some of them, their atmospheres become distended and stripped away by their star, but that takes a long time and being very, very close to the star. The increased temperature on the surface of Jupiter would mean more particles are moving fast enough to escape, but it still wouldn't be boiling.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on April 07, 2017, 04:14:34 PM
If it passed that close, wouldn't we lose our Moon, atmosphere, and oceans? Wouldn't that alter our orbit, too?

It might be a fragmentation of Earth (tidal forces).
My gut feeling tells me the Moon would become a new satellite of Jupiter. 350-400 thousand kilometers (Earth-Moon distance) is between the distances Io and Amalthea orbit Jupiter.

We'd fry from the radiation.  That would put Earth inside Jupiter's huge Van Allen belts, and they are INTENSE.

I'm not so sure. Earth has a strong magnetic field as well. And being inside Jupiters' radiation belts (between Jupiter and its belts) isn't a problem, being within is... ;)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on April 07, 2017, 08:19:10 PM
I meant within...

-And I suspect that at that very closer range, the heat Jupiter radiates might be non-trivial, too.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on April 07, 2017, 09:10:12 PM
I meant within...

Just pullin'...  :)

-And I suspect that at that very closer range, the heat Jupiter radiates might be non-trivial, too.

Dunno. Jupiter radiates more energy then it receives from the Sun (at its current distance of course), but that's in the infrared.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on April 07, 2017, 09:19:16 PM
I thought that's what I said.

450 miles away is LEO or close, and Earth's environment wouldn't be improved by even a minor heat source added...
Title: Re: Astronomy/cosmology questions...
Post by: Geo on April 07, 2017, 09:25:00 PM
I think Earth's environment would already be wrecked by tidal forces before heat became a problem.

What interests me more is what would happen with Earth's 'husk' so to speak once the close encounter was over. Would it be sling into the Sun, or outer space? Or would the 'remains' become a satellite of Jupiter in one way or another (ring system, coalescing again into a sphere, although a molten one to start with,...).
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on April 07, 2017, 09:30:00 PM
I'm sure you're right - probably ocean tides higher than Everest.

Depends on velocity and vector, ect.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on April 08, 2017, 03:30:56 AM
Jupiter still gets most of its energy from the sun. It gets a little extra from the fact that it's still slowly contracting, which turns gravitational potential energy into heat. If Jupiter were the same distance from the sun as us, it would be at about the same temperature as us. It's also big, so it's capturing a large chunk of the sun's energy and redirecting a portion of it at us, but mostly in the infrared. We would not like that.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on April 26, 2017, 08:50:49 PM
Mystery of the universe's Cold Spot deepens – it's not a supervoid (http://alphacentauri2.info/index.php?topic=19283.0)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on May 03, 2017, 05:18:34 PM
Pulsars, Not Dark Matter, May Be Responsible For Excess Gamma-Ray Glow At Milky Way's Centre (http://alphacentauri2.info/index.php?topic=19325.msg105225#msg105225)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on May 12, 2017, 07:04:07 PM
Stephen Hawking and Others Pen Angry Letter about How the Universe Began (http://alphacentauri2.info/index.php?topic=19377.0)
Hawking offers rare public opinion for which he's qualified
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 23, 2017, 02:33:16 AM
I'm trying to write blog posts more frequently, especially now that I'm not busy and have no excuses. To that end, if you guys have any questions about astronomy (and to a lesser extent, math and physics), fire away. If it's a quick question, you'll get a quick answer here. But if it's a question for which the answer can involve a story and some terrible MS Paint illustrations and maybe a bit of math (and I think it would be a fun thing to write about), I'll put together a blog post to answer it. I'll try to get posts out within a week or so, because my hope is that the pressure of someone asking me a question will nudge me into writing.

If this doesn't appeal to anyone here, oh well. If it does, cool, and thanks.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on May 23, 2017, 03:12:43 AM
...You know, there's quite a few science articles linked here in recent months that you could share reactions/thoughts about...
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 23, 2017, 03:57:40 AM
I had a feeling you might say that. If you notice, I tend to respond to direct questions but not to posted articles. Part of this comes from the fact that I tend to withhold judgment on cutting edge stuff in astronomy. I'm aware of how much I don't know and I'm not terribly interested in getting into the weeds about stuff where the best current answer is just that we have to wait for more data. What I like talking about most is (a) how we got to our current state of knowledge, (b) how astronomy gets done, and (c) what it all means. I like telling stories more than I like getting into debates, and questions are a good way to frame stories.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on May 23, 2017, 05:16:18 AM
I'm trying to write blog posts more frequently, especially now that I'm not busy and have no excuses. To that end, if you guys have any questions about astronomy (and to a lesser extent, math and physics), fire away. If it's a quick question, you'll get a quick answer here. But if it's a question for which the answer can involve a story and some terrible MS Paint illustrations and maybe a bit of math (and I think it would be a fun thing to write about), I'll put together a blog post to answer it. I'll try to get posts out within a week or so, because my hope is that the pressure of someone asking me a question will nudge me into writing.

If this doesn't appeal to anyone here, oh well. If it does, cool, and thanks.

Okay. Here's one for you. It may or may not be cosmic. Is all energy the same in that it travels in waves, and we just perceive it differently as light or heat or sound or earthquakes, ( as examples) depending on frequency and amplitude?  Or is it particles, particles traveling in waves, or some of each ?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on May 23, 2017, 04:09:41 PM
I've never quite gotten why astronomy/cosmology thinks our observations tell us anything relevant about the mass of the universe within several orders of magnitude.  Stands to reason that there's a distinctly non-trivial amount of cosmic gas/dust and other non-radiating matter out there making estimations nothing but poorly-informed guesses...
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 23, 2017, 05:44:54 PM
Questions, cool. Thanks, guys. I'll get to them in a bit. In the mean time, here's a post (http://anomalous-readings.blogspot.com/2017/05/rungs-all-way-down.html) on the cosmic distance ladder.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on May 23, 2017, 09:21:22 PM
As the best of our instruments have become far more refined in the last few decades, have there been any significant advances in the range of parallax measurements?  ISTR observations six months apart being good for measuring distance on the order of something 11lyrs.  Is that anything like it currently stands?
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on May 23, 2017, 10:58:56 PM
No hurry. It's not like I need the info to make a decision.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 24, 2017, 12:51:17 AM
As the best of our instruments have become far more refined in the last few decades, have there been any significant advances in the range of parallax measurements?  ISTR observations six months apart being good for measuring distance on the order of something 11lyrs.  Is that anything like it currently stands?

The first star for which we accurately measured the parallax--61 Cygni--is 11 light years away, and that was in 1838. We've been able to do about 1000 light years for awhile. But there is a spacecraft in orbit right now--Gaia--which will get us to the galactic core, which is roughly 30,000 light years distant.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 24, 2017, 01:01:06 AM
I've never quite gotten why astronomy/cosmology thinks our observations tell us anything relevant about the mass of the universe within several orders of magnitude.  Stands to reason that there's a distinctly non-trivial amount of cosmic gas/dust and other non-radiating matter out there making estimations nothing but poorly-informed guesses...

The quick answer to this question is that nothing doesn't radiate. We observe interstellar and intergalactic dust because it (a) absorbs radiation (a process known as extinction, which reddens the spectra (in a way that is different from Doppler redshift) of background objects) and (b) emits radiation. We know atoms emit radiation simply because they have a temperature and therefore must.

But even for something like cold clouds of neutral hydrogen atoms all by their lonesome, electrons randomly make jumps between two adjacent energy levels that gives off radio waves at the (famous?) 21 cm line. Part of the reason we suspect there's dark matter out there is because we can detect the motion (from Doppler shifts of this line) of hydrogen gas way out past where the Milky Way's stars end, and it's still being pulled around by gravity.

When galaxies and galactic clusters collide, the gas heats up tremendously and emits brightly in the x-ray, which we can detect on cosmic scales. This also lets us measure the mass of gas and dust, which far outstrips the mass of all the stars we can count in a galaxy or cluster. So we have pretty good estimates for how much gas and dust are out there.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on May 24, 2017, 01:21:33 AM
But there is a spacecraft in orbit right now--Gaia--which will get us to the galactic core, which is roughly 30,000 light years distant.
Orbiting Earth - or further out from the Sun?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 24, 2017, 01:48:40 AM
It's at Sun-Earth L2, which gives it a 10% longer baseline for parallax measurements. What really makes it better at measuring parallax, however, is that it's an all-sky survey that can accurately measure brightness across a very wide band. This means that for any particular star it's observing, it can compare that star's position to many, many other background stars (and quasars) at the same time.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on May 24, 2017, 07:07:24 AM
As the best of our instruments have become far more refined in the last few decades, have there been any significant advances in the range of parallax measurements?  ISTR observations six months apart being good for measuring distance on the order of something 11lyrs.  Is that anything like it currently stands?

The first star for which we accurately measured the parallax--61 Cygni--is 11 light years away, and that was in 1838. We've been able to do about 1000 light years for awhile. But there is a spacecraft in orbit right now--Gaia--which will get us to the galactic core, which is roughly 30,000 light years distant.

A follow up on this one. If there's the possibility to put a perfect parallax on stars that much distant, how about putting a parallax on the tiny motions of stars within a couple parsecs with a crop of planets orbiting it? Would it be possible to detect the wobble sideways (from the Solar System's point of view) of the gravity interaction between star and planets?
Kind of a elaboration/confirmation on results of the radial velocity method.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 24, 2017, 03:57:54 PM
Absolutely, yes. That method is called astrometric planet detection, and it's one of Gaia's mission goals. That said, it's an extremely difficult measurement to make and so far (not counting whatever Gaia may do) no planets have been found by this method.

The case of Jupiter is a quick example of why this measurement is hard. If we imagine the solar system consists only of the sun and Jupiter (not far off from the truth), then the two bodies orbit their common barycenter. This means they complete that orbit in the same amount of time. Jupiter's orbit takes 12 years, so it also takes the sun 12 years to move around the system's barycenter. Because the sun is ~1000 times as massive as Jupiter, the center of mass is 1/1000 the way to Jupiter, which means the sun (seen from another star system) is moving a distance only about 7% longer than its diameter, and it's taking 6 years to do that.

Seen from, say, our closest neighbor Alpha Centauri, that's an angular change of about 7 milliarcseconds, where a milliarcsecond is 1/1000 of 1/3600 of a degree. For reference, the moon is about 1/2 a degree wide.

Another complication is that the radial velocity and transit methods work best for systems that are edge on to us, but the astrometric method works best for systems that are face on to us. So it's difficult for one method to be used to confirm the results of the other.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 24, 2017, 04:01:10 PM
Not sure why I went and did all that math right now. I think it's just been awhile, what with me being out of school for half a year...
Title: Re: Astronomy/cosmology questions...
Post by: Geo on May 25, 2017, 01:22:08 PM
Another complication is that the radial velocity and transit methods work best for systems that are edge on to us, but the astrometric method works best for systems that are face on to us. So it's difficult for one method to be used to confirm the results of the other.

I should mention I'm a bit self-studied in astronomy. I kinda asked the question for those exoplanetary systems where the exoplanets orbit their parent star(s) are between edge -and face on with the latest tools.

A couple questions on Lagrange point matters. So this Gaia probe has a roughly 10% better baseline with the Sun-Earth L2 point only being 1% of the Sun-Earth distance further out (1,5 million km)?

On another note, it is known that a couple other planets in our system have small objects orbiting in their respective L4-L5 points. Especially Mars and Jupiter. I kinda wondered why, over the eons, these objects didn't clump to bodies large and massive enough to become roughly spherical. Think Vesta-sized. Is there some peculiarity on how those objects move around in any particular L4-L5 points that precludes the formation of larger bodies? I read about Lissajous orbits around those points, but with a sufficient number of objects I expected encounters to be common.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 25, 2017, 05:53:52 PM
A couple questions on Lagrange point matters. So this Gaia probe has a roughly 10% better baseline with the Sun-Earth L2 point only being 1% of the Sun-Earth distance further out (1,5 million km)?

Oops, no. Just a brain fart on my part. Baseline is only 1% better.

Quote
On another note, it is known that a couple other planets in our system have small objects orbiting in their respective L4-L5 points. Especially Mars and Jupiter. I kinda wondered why, over the eons, these objects didn't clump to bodies large and massive enough to become roughly spherical. Think Vesta-sized. Is there some peculiarity on how those objects move around in any particular L4-L5 points that precludes the formation of larger bodies? I read about Lissajous orbits around those points, but with a sufficient number of objects I expected encounters to be common.

In general, Lissajous orbits are something we establish for probes at L1 and L2 because those points are only metastable. Objects at those points tend to fall out, so it helps to have an orbit that sort of naturally takes you in and out and around those Lagrange points.

L4 and L5, on the other hand, are very stable, and objects put there tend to stay there. This is why the Trojan asteroids at Jupiter's L4 and L5 points occupy a pretty wide swath of Jupiter's orbit, because gravitationally those points are more like shallow depressions. (That said, because the Trojans are often not exactly the same distance from the sun as Jupiter, they move at slightly different speeds and follow something called a Tadpole orbit.)

As far as why they don't accrete into something bigger, there are a couple reasons. The first is that, while L4 and L5 are mathematically stable if you just consider the restricted three-body problem, the vagaries of the solar system (mostly resonances with Saturn) mean that staying there isn't completely problem-free. Trojans do tend to get ejected, and that hampers growth by accretion.

The other problem is that there's just not enough material. Accretion into a planetesimal is a runaway process, but if you don't have enough mass packed densely enough, that runaway process never starts. Additionally, there's not a lot of gas left in interplanetary space, which causes drag that slows material down, increasing the likelihood of objects eventually colliding and making those collisions softer. Softer collisions are better for objects sticking together rather than blowing apart.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 26, 2017, 06:09:04 PM
Okay. Here's one for you. It may or may not be cosmic. Is all energy the same in that it travels in waves, and we just perceive it differently as light or heat or sound or earthquakes, ( as examples) depending on frequency and amplitude?  Or is it particles, particles traveling in waves, or some of each ?

What energy is turns out to be a pretty complicated question. Historically, one of the earliest conceptions of energy came out of Newton's mechanics. Because Newton talked in terms of force, physicists noticed (mathematically and observationally) that when a force is applied to an object, "work" is done on the object which moves it. You can calculate the amount of work done, and it turns that this quantity is conserved.

So when you drop a ball, the force of gravity does work bringing the ball to the ground. A certain amount of gravitational energy turns into kinetic energy, which then turns into heat and sound when the ball hits the ground. (The force of the ball hitting the ground does work on the ground and the air around the ball.)

In modern physics, force is still important but fields are arguably more fundamental. Nowadays, physicists frame things in terms of quantum field theory. This says that all space is pervaded by fields (gravitational, electromagnetic, etc.) and that these fields contain energy. When the fields are perturbed in some way, they emit energy. For example, messing with the electromagnetic field produces light. Quantum physics tells us that light (along with basically everything) has both wave and particle nature. Light seems to travel as a wave but collide with other objects like a particle.

But in a very real sense, the energy of a photon slamming into another particle is kinetic--that is, due to its motion. So we can think of energy as having two modes: stored in fields, or expressed through motion. When you build up charge in a capacitor, energy is being stored in the electric field. When you close a circuit and induce a current, the energy moves from the electric field to the motion of the electrons.

At a very fundamental level, energy from motion will always be both wave and particle, because of the wave-particle duality of quantum mechanics. But at higher levels of abstraction, that might not matter. When a bullet travels through the air, it possesses kinetic energy, and quantum mechanics tells us how to calculate the "wavelength" of a bullet, but it turns out to be so ludicrously small (~10^-34 m) as not to matter. On our scale, a bullet is a particle.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on May 26, 2017, 08:22:18 PM
Thank you, Lorizael, you do this so well.

This would have made a nice film in my day, but quantum mechanics was for nuclear physicists, not for the general public. I hope that you can find a way for your explanations and illustrations to reach a broader audience, and to earn a living from it.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 27, 2017, 01:25:56 AM
Aw, shucks.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on May 27, 2017, 09:37:56 AM
The other problem is that there's just not enough material. Accretion into a planetesimal is a runaway process, but if you don't have enough mass packed densely enough, that runaway process never starts. Additionally, there's not a lot of gas left in interplanetary space, which causes drag that slows material down, increasing the likelihood of objects eventually colliding and making those collisions softer. Softer collisions are better for objects sticking together rather than blowing apart.

So, in short, if it doesn't happen during the latter stages of the planetary formation process in a young star system, it's very unlikely to happen again. And better chances further out where distances between gas giants are usually much larger as well, as well as lower masses of the gas giants residing in the outer orbits.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on June 02, 2017, 02:05:53 PM
LIGO spots a third black hole merger, tightens mass limits on gravitons (http://alphacentauri2.info/index.php?topic=19517.0)
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on June 04, 2017, 09:00:44 PM
I was hoping for something other than another black hole-black hole merger this time, but apparently detecting this many in so short a period of time has some scratching their heads. That is, stars and other dots in space rarely ever collide, because space is so big compared to the size of gravitationally collapsed objects, unless those objects basically started out next to each other anyway. And if these black holes started out next to each other, why did it take until they had both lived their entire lives as stars and then collapsed into black holes before they merged?
Title: Re: Astronomy/cosmology questions...
Post by: Geo on June 05, 2017, 09:14:51 AM
I was hoping for something other than another black hole-black hole merger this time, but apparently detecting this many in so short a period of time has some scratching their heads. That is, stars and other dots in space rarely ever collide, because space is so big compared to the size of gravitationally collapsed objects, unless those objects basically started out next to each other anyway. And if these black holes started out next to each other, why did it take until they had both lived their entire lives as stars and then collapsed into black holes before they merged?

Maybe the collapse also released huge amounts of stellar gas, creating a denser environment in which at least one of the stars 'brakes' into an ever closer orbit?
In any case, the gravitational equilibrum changes when a massive object occupying a certain space 'suddenly' becomes a pinpoint. The tides become different.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on June 05, 2017, 07:28:28 PM
I read it and think that there's some kind of kernel for a Larry Niven story. Weaponized gravity wave communication transmitters in a Pak Protector war or something.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on June 06, 2017, 10:30:57 AM
I read it and think that there's some kind of kernel for a Larry Niven story. Weaponized gravity wave communication transmitters in a Pak Protector war or something.

The closest I can remember to that is a human-descended Pak Protector and his sidekick sling around a neutron star to change course and during the manoeuver the human Pak fires some bullets which somehow would intersect with the trajectory the nearest of their native Pak pursuers follows.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 05, 2017, 04:07:20 PM
Okay, so I clearly bungled this whole plan. Sorry for not actually giving you guys lengthy responses to your questions. BU, I'm working on a post about gas and dust. In the mean time, here's something about Newton and gravity.

http://anomalous-readings.blogspot.com/2017/07/from-earth-to-moon.html (http://anomalous-readings.blogspot.com/2017/07/from-earth-to-moon.html)
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on July 10, 2017, 05:39:39 PM
I dislike horseshoe orbits.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 10, 2017, 11:41:41 PM
What'd they ever do to you?
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on July 11, 2017, 01:15:35 AM
Made me frantically search for gifs while my feeble brain melted trying to understand. Brain goo is very difficult to get out of carpet, fyi.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on July 11, 2017, 04:43:06 AM
The thing to remember about horseshoe orbits is that the horseshoe shape only looks that way relative to the Earth, which is also moving around the sun. If you look at an object in a horseshoe orbit relative to the sun, it will look just like any old asteroid with a slightly elliptical orbit. Relative to the earth, though, it speeds up and slows down and ends up looking weird.

Calling it a horseshoe orbit is something of a misnomer. It would be like if we said that planets have a loop-the-loop orbit because, from the earth's perspective, they sometimes loop backwards. No, planets are just orbiting in ellipses, and because they orbit at different speeds, more distant planets will appear to move backward when closer, faster planets pass them up.

(The difference, though, is that a horsehoe orbit object does weird stuff because it is close to the earth and being affected by its gravity. But the end result is still basically just an ellipse from the perspective of the sun.)
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on July 11, 2017, 03:46:03 PM
Unfortunately, everything I first saw/read was all from the earth perspective and was very unhelpful to me. A proper non-geocentric gif helped a lot.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on July 12, 2017, 08:57:19 AM
Be glad you didn't start with lissajous curves/orbits then. :)
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on July 14, 2017, 07:08:30 PM
I thought this was interesting. It makes sense now that I think about it. Still, it kind of amazed me that one would neither freeze, nor boil, nor explode, at least in the short term.

http://www.webcitation.org/68Aef3glC?url=http%3A%2F%2Fimagine.gsfc.nasa.gov%2Fdocs%2Fask_astro%2Fanswers%2F970603.html (http://www.webcitation.org/68Aef3glC?url=http%3A%2F%2Fimagine.gsfc.nasa.gov%2Fdocs%2Fask_astro%2Fanswers%2F970603.html)
Title: Re: Astronomy/cosmology questions...
Post by: gwillybj on July 15, 2017, 03:56:00 AM
Be glad you didn't start with lissajous curves/orbits then. :)
You had to make me look, didn't you? ;)
https://en.wikipedia.org/wiki/Lissajous_orbit
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on July 15, 2017, 05:32:54 AM
That one didn't bother me. Maybe there's nothing left to melt.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on July 15, 2017, 02:22:15 PM
Be glad you didn't start with lissajous curves/orbits then. :)
You had to make me look, didn't you? ;)
https://en.wikipedia.org/wiki/Lissajous_orbit

Not particularly you. :)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on August 22, 2017, 10:46:37 PM
Lori, how long has it been since a lunar month was 27 days?

How close is it to 28 days exactly, now?  Surely not EXACTLY 28 days, right?  The would be one heck of a coincidence...
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 23, 2017, 02:14:25 AM
Well, so, what do you mean exactly by the lunar month? If you're talking about the time it takes for the moon to complete one orbit around the Earth (relative to the fixed stars), that's about 27.3 days. If you're talking about the time it takes to go through a full set of lunar phases, from one new moon to another, that's roughly 29.5 days.

Over the last few hundred million years, the distance between the Earth and moon has increased by an average of slightly more than 2 cm per year. From that, and using Kepler's laws, you can do a little math and find that the orbital period (called the sidereal month) would have been exactly 27 days about 140 million years ago.

If you're talking about when the lunar phases took 27 days (called the synodic month), that would have been when the orbital period was just over 25 days long. Doing the same math as above, and assuming the recession rate maintains that average even further back, then that would have been about 950 million years ago.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on August 23, 2017, 02:29:33 AM
Interesting.  Thanks.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 23, 2017, 03:30:28 AM
No problem. And of course, that all ties into eclipses. About a billion years ago, the apparent size of the moon was maybe 5% larger, so the moon would always cover up the sun if it passed between the earth and it. In another billion years, as the moon gets farther away, it will never be able to totally eclipse the sun. We're so special.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on August 23, 2017, 02:50:41 PM
No problem. And of course, that all ties into eclipses. About a billion years ago, the apparent size of the moon was maybe 5% larger, so the moon would always cover up the sun if it passed between the earth and it. In another billion years, as the moon gets farther away, it will never be able to totally eclipse the sun. We're so special.

So were the dinosaurs, if any species of it was intelligent enough to admire the show. ;)
There was an article in one of our news sites writing about the end of full totality eclipses as well. IIRC they came up with 650 million years before the Moon is too far out to cover the Sun completely.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on September 22, 2017, 06:16:48 PM
Lori, come straighten us out, please...
http://alphacentauri2.info/index.php?topic=19956.msg107971#msg107971 (http://alphacentauri2.info/index.php?topic=19956.msg107971#msg107971)
Title: Re: Astronomy/cosmology questions...
Post by: Geo on October 13, 2017, 07:15:05 AM
A couple of questions about Haumea because of a recently released article.

https://www.sciencedaily.com/releases/2017/10/171012093350.htm (https://www.sciencedaily.com/releases/2017/10/171012093350.htm)

I'll post the excerpt and my question(s) below it.

Quote
Haumea is an interesting object: it rotates around the Sun in an elliptic orbit which takes it 284 years to complete (it presently lies fifty times further from the Sun than the Earth),
and it takes 3.9 hours to rotate around its axis, much less than any other body measuring more than a hundred kilometers long in the entire Solar System. This rotational speed causes it
to flatten out, giving it an ellipsoid shape similar to a rugby ball. The recently published data reveal that Haumea measures 2,320 kilometers in its largest axis -- almost the same as Pluto --
but lacks the global atmosphere that Pluto has.

Is there a likelihood that Haumea, instead of being a single body, is two 'lobes' connected somewhat like 216 Kleopatra, but closer?
It's just that I find it odd Haumea pulls a Jinx-like object on us like in Larry Niven's Known Space novels.

Quote
First Trans-Neptunian Object With a Ring

According to the data obtained from the stellar occultation, the ring lies on the equatorial plane of the dwarf planet, just like its biggest satellite, Hi´iaka, and it displays a 3:1 resonance
with respect to the rotation of Haumea, which means that the frozen particles which compose the ring rotate three times slower around the planet than it rotates around its own axis.

Assuming that the longest axis of Haumea also lies in its equatorial plane, I wonder if this ring would orbit the dwarf planet in an ellipsoid shape as well instead of the usual circular one.
I mean, the orbital velocities needed to stay at a given distance of the surface are not 'circular' in respect to this world's equator.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on October 14, 2017, 06:23:41 PM
Ack. I was going to show you a figure from the paper to help answer your question, but I just realized I only have access to the paper when I'm at work. I mean I could probably finagle something, but I'm lazy and can make do.

Is there a likelihood that Haumea, instead of being a single body, is two 'lobes' connected somewhat like 216 Kleopatra, but closer?
It's just that I find it odd Haumea pulls a Jinx-like object on us like in Larry Niven's Known Space novels.

So before this set of observations, the shape of Haumea was known only through its lightcurve. That is, it would periodically get bright and dim, and we can infer from that (after taking into account its distance, angle with the sun, etc.) that it's dim when we're seeing a narrow profile and bright when we're seeing a wide profile. And yeah, there are a bunch of assumptions baked into that kind of observation, so it's possible to get the shape wrong. But the occultation done here mostly rules all that out.

This set of observations was done at the same time from a dozen telescopes at different latitudes on Earth, which means we see the occulted star at different angles. This means you can trace different lines across Haumea representing the star's path as seen from different points on Earth. For however long the star is invisible (because it's behind Haumea) from that angle, you get Haumea's width at that line. At no point did the star disappear, blink back, and disappear again, which is what you'd expect for lobes. Instead, it remains completely occulted for some period and is then visible again.

Quote
Assuming that the longest axis of Haumea also lies in its equatorial plane, I wonder if this ring would orbit the dwarf planet in an ellipsoid shape as well instead of the usual circular one.
I mean, the orbital velocities needed to stay at a given distance of the surface are not 'circular' in respect to this world's equator.

This is a difficult question to answer. I know the paper concludes that the ring is circular, and they do this by identifying points on the ring via the occultation and then connecting the dots to get the projection of the ring from our angle. If you tilt the projection to line up with the equator, you get a circle.

Whether or not the ring should be circular is something else to consider. The question is whether Haumea's shape "excites" the orbit of the ring particles. Circular orbits have the lowest energy for an orbit of a given semi-major axis. If you pump energy into the orbit, it becomes more eccentric (elliptical) until eventually particles are able to escape. But there's no simple answer for whether or not a particular configuration of stuff is going to excite an orbit; it involves a lot of perturbation analysis and numerical integration. (This answer is somewhat of a cop out because my knowledge of complicated orbital mechanics is sketchy.) That said, general features which could excite an orbit include resonances. The article mentions the ring's orbit being very close to a 3:1 resonance with Haumea's own rotation. That is the kind of orbital parameter that could spice things up. /me shrugs.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on October 14, 2017, 10:30:32 PM
Thanks a ton, Lorizael.  :)

Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on October 15, 2017, 02:22:16 AM
Obviously I'm out of my depth in this discussion, but for purposes of an orbit, isn't it the point of center mass what matters rather than the distance between the two surfaces, or the density of the planet? A moon circling a gas giant or a round rock, or a rugby shaped rock of the same mass would have the same orbit based on the speed of the moon and distance between the centers of mass, wouldn't it?

A Moon crossing the Andes of Earth or the seams of Rugby shouldn't have a measureable effect on it's orbit, should it?

No hurry on this one, not like it's haunting my thoughts or anything.

Title: Re: Astronomy/cosmology questions...
Post by: Geo on October 15, 2017, 10:25:07 AM
You're of course right, Rusty. And to bring the punch home, Haumea's biggest moon (Hiʻiaka) has a similar excentricity as the Moon shows in respect to Earth.
But I keep finding it odd that Haumea has such a weird shape, with two huge protusions along its equator. Something must have caused it so that not the whole equator is more or less evenly 'flattened out', as to have more the shape of a disc. A more spread out distribution of the core mass? In any case, to me if felt like the ring system could have behaved differently then it appearantly does (circular orbit around Haumea as well).
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on October 15, 2017, 02:32:56 PM
A Moon crossing the Andes of Earth or the seams of Rugby shouldn't have a measureable effect on it's orbit, should it?

It absolutely does, which is how we're able to produce maps like this:

(https://upload.wikimedia.org/wikipedia/commons/5/56/Geoids_sm.jpg)

This is the "geoid" and is sometimes referred to as the true figure of the Earth, gravitationally speaking. We measure this with satellites by very carefully tracking deviations from the orbit we expect. The thing to remember about gravity is that the "real" way to calculate the gravitational force on an object is to add up the mass and distance of every single particle that could attract the object. So if you have more particles closer to you, there's more gravity.

Thankfully, we don't actually have to do this because Newton proved a theorem (shell theorem) which says that you can treat a perfectly symmetric sphere of uniform density as if it were just a single point of mass at the center. If you're very far away from something that's roughly a sphere, you can pretend the shell theorem applies and everything works out pretty well. The closer you get/the more deformed the object is, the less you can get away with it.

A final note is that even with satellites measuring orbital deviations, we're basically still just pretending the Earth is a sphere. But we're pretending it's like a couple thousand slightly different spheres stacked on top of each other (a mathematical trick known as spherical harmonics). Doing that is still way, way easier than counting all the grains of sand and measuring their gravity...
Title: Re: Astronomy/cosmology questions...
Post by: Geo on October 15, 2017, 02:59:40 PM
Guess that shows we have different ideas about 'measurable', Lori.
I'm definitely a layman in these matters. ;)
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on October 17, 2017, 01:59:50 AM
That is so cool....especially since I'm not in school and don't have to solve those kinds of story problems! Thanks, Lorizael! I should have known, the interconnectedness of all things. Gravity as Zen.

I imagined the actual earth shape was relatively smoother, but with more of an apparent belly bulge than that. A little less spherical.
------------------------------------------------

So this has me wondering, what factors create a rugby planetoid, rather than the more familiar spherical ones?

For example, is this more likely to happen when the denser core of a moon/planet does an amoeba style complete separation while still travelling in the same orbit, resulting in a faster and slower Rugby? Or is it the lack of rotation, or rotation perpendicular to the axis of orbit that is the key factor?   Or is it something else, more like a ball of playdough in orbit, collecting gravel and dust in it's path? Or maybe more of a giant teardrop of liquid gas gathering droplets of other gasses on it's leading bulbous end?

Again, no hurry on this one.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on October 21, 2017, 08:38:17 PM
I imagined the actual earth shape was relatively smoother, but with more of an apparent belly bulge than that. A little less spherical.

Oh, I mean, the real physical shape of the Earth is nearly a perfect sphere. The radius of the Earth is ~6400 km and Everest is 8.8 km high. That map is just a map of the relative strength of gravity from one location to the next. Buttttt, if you pretend the Earth is a perfect fluid with the current density distribution, then the "fluid" of the Earth would flow so that the Earth's shape resembled that geoid. (Although that map is an exaggeration of the true geoid, I think.)

Quote
So this has me wondering, what factors create a rugby planetoid, rather than the more familiar spherical ones?

For example, is this more likely to happen when the denser core of a moon/planet does an amoeba style complete separation while still travelling in the same orbit, resulting in a faster and slower Rugby? Or is it the lack of rotation, or rotation perpendicular to the axis of orbit that is the key factor?   Or is it something else, more like a ball of playdough in orbit, collecting gravel and dust in it's path? Or maybe more of a giant teardrop of liquid gas gathering droplets of other gasses on it's leading bulbous end?

Again, no hurry on this one.

The answer is mostly rotation. Absent any other forces, a gravitating mass will coalesce into a sphere. If the mass is made up of rocks and other hard, pointy objects and is small enough, gravity can't reshape it into a sphere and it retains whatever clumps originated from the collisions that formed it. If it's rotating, then the faster it rotates, the more of an equatorial bulge it will have, as you pointed out. Direction relative to orbit shouldn't matter in general, although that does come up with the YORP (https://en.wikipedia.org/wiki/Yarkovsky%E2%80%93O%27Keefe%E2%80%93Radzievskii%E2%80%93Paddack_effect) effect, where pressure from solar radiation can mess with an asteroid's spin and shape.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on October 22, 2017, 07:31:03 AM
But why isn't the equatorial bulge not of the same diameter all along it?
As far as I can tell there's a difference of hundreds of kilometers between the shortest an longest equatorial radius.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on November 23, 2017, 05:48:36 PM
Dark Matter and Energy Don't Exist: Astronomer Claims to Solve Universe's Greatest Mysteries With New Model (http://alphacentauri2.info/index.php?topic=20194.0)
Astrophysical Journal article linked - something about scale invariance.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on November 23, 2017, 06:18:42 PM
Dark Matter and Energy Don't Exist: Astronomer Claims to Solve Universe's Greatest Mysteries With New Model ([url]http://alphacentauri2.info/index.php?topic=20194.0[/url])
Astrophysical Journal article linked - something about scale invariance.


I assume this is a mathematical model.

Having typed that, I wonder what else it could be... and could they get countertop expanding universe kits in the stores by Christmas.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on November 23, 2017, 07:23:36 PM
I'll admit I don't have a strong grasp on what this guy is saying, but here's what I can piece together. In general relativity, mass-energy acts like regular old gravity in most situations. But there are times when general relativity diverges from a basic attractive force. One of those times is when the density of some amount of stuff remains constant as space expands. In those situations, general relativity actually produces a repulsive effect that we call the cosmological constant and which we observe as dark energy's accelerated expansion of the universe.

What this guy is saying is that the scale invariance of empty space--that is, the idea that empty space looks the same even as the universe expands or contracts--should similarly act as a cosmological constant and cause a dark energy-like effect. I don't know enough of the underlying physics and math to evaluate this claim. It could be true, but it could also be true that he's conflating terms and concepts that look similar.

He then goes on to say that this effect should also produce extra acceleration on galactic scales. This is where he's getting rid of dark matter. And this is where he runs into a problem. The first evidence for dark matter was the fact that stuff in the universe (at the edges of galaxies, in galactic clusters) appears to be moving more quickly than would be suggested by the mass we can see. So the dark matter hypothesis is that there is extra matter we can't see that also contributes to gravitational acceleration. But of course, an alternative hypothesis is just that gravity produces a little extra acceleration at very large scales. This is what MOND and other proposals suggest. And that's where this guy is going, too.

The problem is that we have evidence for dark matter that manifests as more than just extra acceleration. As I talked about in a previous post, if dark matter doesn't interact with regular matter, then sometimes dark matter and regular matter won't be in the same place. If we can see effects of gravity in places where this is no regular matter, that's a very big hint that we're seeing the effect of non-interacting matter--dark matter. A little bit of extra acceleration baked into your equations can't account for this.

The strongest piece of evidence for the separation between dark matter and regular matter comes from the CMB. The cosmic microwave background is an imprint of the universe from 380,000 years after the big bang. The very cool part about the CMB is that it records the acoustics of the early universe. The universe was ringing like a bell as matter contracted and expanded. Given the density, size, and composition of the universe when the CMB formed, you can predict which frequencies of contraction and expansion would have been most prominent at that moment.

But this is also where you can separate regular and dark matter. Regular matter contracts, heats up, and expands again. Dark matter, because it doesn't interact, just contracts. This means the contraction of dark matter interferes with the expansion of regular matter, which distorts the peaks and troughs of the CMB. When you look at the CMB spectrum, it perfectly matches a universe in which peaks representing matter expanding are stunted by the effects of dark matter contracting. No theory that just adds an extra bit of acceleration on large scales can account for this, because the extra gravity of dark matter is opposing the gravity of regular matter rather than adding to it.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on November 23, 2017, 07:36:58 PM
You've read the Astrophysical Journal article?
https://arxiv.org/abs/1701.03964
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on November 24, 2017, 01:55:14 AM
I read the abstract and skimmed the article. Much of the math is beyond me, at least until the general relativity bits reduce to more familiar stuff. So I can't really speak to the theoretical underpinnings. But I'll note that the ApJ paper only covers consequences for a cosmological constant. There's another paper that deals with the dark matter stuff.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on November 24, 2017, 04:18:32 AM
Okay, as I've said before, black matter and black energy often sound like scientific fudge factor nonsense in an ether/humors/cold fusion sort of way- essentially secret magic that explains what they observe and don't understand.

BUT I"VE BEEN CONVINCED THAT SUCH STUFF EXISTS BECAUSE OF CROSS REFERENCED OBSERVATIONS, MEASUREMENTS, CALCULATIONS THAT FIT, etc. IT EXISTS.

So at the moment I'm wondering what it might be. A term other than "dark".  For example, could dark matter be simply something like dust made of quarks, which only has mass & effects in the aggregate? 

Or might "tangential", "extra-dimensional", or "off-spectrum" be better descriptors with fewer connotations for this energy and matter ?
















 
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on November 24, 2017, 03:36:56 PM
Dark matter has acquired negative connotations, but it's really a very apt name. Matter that doesn't interact with light--dark matter.

In terms of what it might be, there are two broad categories: MACHOs and WIMPs. The former are MAssive Compact Halo Objects and refer to objects made of normal matter that are (a) dim and (b) non-interacting. So this includes things like rogue planets and primordial black holes. Technically, these objects could interact with normal matter and light, but because they are very small the odds of them doing so are extremely slight. So if there were enough of these objects, they could act like dark matter.

MACHOs have fallen out of favor recently because of a few different measurements. One is gravitational lensing. We can actually find planets and dim stars by watching the sky for sudden changes in the brightness of background stars. If a star brightens in just the right way, the conclusion is that another object passed in front of that star and warped the light with its gravity. Because we know how much gravity there is from dark matter, we can predict how often we can see such events. We're not seeing enough, which puts strong limits on the contribution of MACHOs. The other problem is that the big bang lets us predict how much of each element should be out there in the universe, and when we look at primordial gases and stars, we see exactly what we're supposed to see. That wouldn't be the case if most matter in the universe were locked up in MACHOs.

For all that and some other reasons, this is why cosmologists favor WIMPs, which are Weakly-Interacting Massive Particles. This is where you get help from the particle physicists and ask them to dream up weird particles that fit the constraints of cosmological models. They have a bunch of possibilities that can get quite strange, some of which have been ruled out by the LHC and various dark matter detectors we have built underground.

As far as quark dust, that probably doesn't work as a suggestion. Lone quarks can't exist in nature because of something called color confinement. This is a weird concept, but basically there is a property like charge for subatomic particles, but instead of positive and negative, there are three choices. Particle physicists call them colors because why not. Charged particles attract each other, and the same is true for particles with color. The difference is that the force attracting particles with color gets stronger the farther apart they are, so quarks are only seen clumped together with other quarks because a lone quark would be pulled to the nearest other batch of quarks veeeeery strongly.

In nature, the stable varieties are pairs and triplets of quarks. The most stable triplets out there are protons, which are just regular matter. After that you get neutrons, which only last about 15 minutes on their own. Half lives go down pretty quickly after that (millionths of a second kind of thing, produced only in particle accelerators).
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on November 24, 2017, 08:00:56 PM
Thank you very much for that, Lorizael.

What of Dark Energy? Is it simply out of the light spectrum, or is it something weird?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on November 24, 2017, 08:14:51 PM
Also relevant-  A Mysterious Galactic Glow Hints at Hidden Pulsars (http://alphacentauri2.info/index.php?topic=20201.0)
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on November 24, 2017, 11:57:09 PM
Thank you very much for that, Lorizael.

What of Dark Energy? Is it simply out of the light spectrum, or is it something weird?

Basically the only thing known about dark energy is that it acts like a cosmological constant. That is, there's some amount of mass-energy in every bit of space, and it's the same everywhere, and in general relativity that produces a repulsive effect which accelerates the expansion of the universe. As far as what it really is, that's a big mystery.

If you look at quantum physics, it says that the vacuum of space should have energy itself. And since most of space is a vacuum, that would seem to work as a candidate for dark energy. But when you try to calculate how much energy might be in the vacuum (there's not necessarily a definitively correct way to do this), it comes out to be ~120 orders of magnitude (that is, a 1 followed by 120 0s) more powerful than the observed effect of dark energy. So that's a pretty bad prediction.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on November 25, 2017, 05:00:35 PM
A question I've asked concerning relativity/cosmology, that I think is probably crucial.
What is Space? The 300-Year-Old Philosophical Battle Still Rages Today
(http://alphacentauri2.info/index.php?topic=20207.msg108883#new)
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on November 25, 2017, 07:16:21 PM
A question I've asked concerning relativity/cosmology, that I think is probably crucial.
What is Space? The 300-Year-Old Philosophical Battle Still Rages Today
([url]http://alphacentauri2.info/index.php?topic=20207.msg108883#new[/url])


Buncle, I was wondering about that question myself, as I read this thread and some tangents on Wikipedia. To the extent that we don't know what dark energy is, but it acts like a cosmological constant, it's starting to sound suspiciously like "ether."

WHAT IF the key has more to do with the nature of space itself rather than theoretical dark energy? Is space elastic? Is it subject to distortion by force from things like gravity or the big bang?  I guess black holes suggest that. If so isn't it possible that stuff on the fringes of the universe is accelerating because it's entering normal, undistorted space, and our physics is based on our perspective, our world, where mass and weight seem the same at sea level, and adapted as we change altitude, get beyond our atmosphere, Earth's gravity, The Sun's etc., and yet hasn't adapted to the rules of "original space." Or maybe the Universe is something like a pond, the Big Bang a rock tossed into it, and the acceleration we see in the distance is something crossing the compression wave rings distorting the pond's surface.

Well Lorizael, I don't mean to impose on your time trying to explain the unknown. Then again, the nature of space itself is sort of the interesection of philosophy and cosmology and exactly the kind of thing you might like to talk and theorize and speculate about, but if so, do it when you have the time and inclination. 
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on November 27, 2017, 06:22:20 PM
I'm taking this out of order. There's a lot in your post.

Quote
Well Lorizael, I don't mean to impose on your time trying to explain the unknown. Then again, the nature of space itself is sort of the interesection of philosophy and cosmology and exactly the kind of thing you might like to talk and theorize and speculate about, but if so, do it when you have the time and inclination.

I'm glad for the discussion.

Quote
Is space elastic? Is it subject to distortion by force from things like gravity or the big bang?  I guess black holes suggest that.

Einstein's general theory of relativity says exactly that. I'm sure you've seen the depictions of gravity where space is a giant rubber sheet and a black hole is plopped in the middle, causing the sheet to sag downward. This is supposed to convey two ideas: (1) mass distorts space and (2) acceleration due to gravity is really just objects following the curve of space.

Getting a bit into the relationism/absolutism philosophical angle from above, relationism says there is no space, just relations between objects. Mathematically, those relations are coordinates. Like, say, I am 3 miles north and 2 miles east of you, or something like that. Naively, we think of coordinates in a Euclidean way, as happening on a flat plane where triangles and circles behave themselves.

But there are other types of geometries, which you know just by looking at world maps. You have to distort distances (coordinates) in order to get the curved Earth to lay flat. The technical meaning of this is that a curved space has a different "metric" than a flat space, where metric just means "way of figuring out how far away things are from each other."

What general relativity tells us is that mass-energy "distorts" space by changing the metric, changing how you measure distances between objects. According to general relativity, there doesn't have to be a real, physical thing called "space-time" out there containing all the stuff in the universe. You can do perfectly well just thinking about how the metric changes in response to mass.

Quote
If so isn't it possible that stuff on the fringes of the universe is accelerating because it's entering normal, undistorted space, and our physics is based on our perspective, our world, where mass and weight seem the same at sea level, and adapted as we change altitude, get beyond our atmosphere, Earth's gravity, The Sun's etc., and yet hasn't adapted to the rules of "original space."

An important thing to remember about astronomy is that we're looking back in time. We cannot see what is happening to extremely distant galaxies right now. We can only see what was happening to them millions or billions of years ago. So when we observe the accelerating expansion of the universe, we're not seeing very distant galaxies being pulled away from us at ever increasing speeds.

Instead, what we're seeing is that the expansion rate used to be slower in the past. The evidence for this comes from how much light gets stretched out on its journey to us. For relatively nearby objects, there's been a loooot of stretching. But for very, very distant objects, there's been more stretching but not as much as you would expect given how far away the objects are. That means the expansion of space is fast now. It's right here that we see the accelerated expansion.

Quote
To the extent that we don't know what dark energy is, but it acts like a cosmological constant, it's starting to sound suspiciously like "ether."

I am not convinced that aether should be a scientific boogeyman. Sometimes the aether is real. In the 19th century, Faraday postulated that invisible electric and magnetic fields emanated from all charged bodies and that these fields were responsible for the many weird electric and magnetic effects you could produce in a lab. He was right.

In the 20th century, Pauli postulated that an unbalanced equation in nuclear reactions meant there was a tiny, uncharged, non-reacting particle we could never hope to detect that made the math work. It got called the neutrino. He was right and we detected it.

Maybe dark matter and dark energy will go the way of the aether. Maybe they'll go the way of electric fields and neutrinos. I'm not sure we're in a position to judge and I don't think any supposed parallel is evidence that something is amiss in cosmology.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on November 30, 2017, 12:11:28 AM
I guess I can see your point on the aether thing. Isn't the Bell labs radio telescope discovery of the background noise from The Big Bang a similar example? Something ubiquitous that eventually had no other credible alternative explanation?

Some of the other parts of your answer I may follow up on when I have a better grasp of it.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on November 30, 2017, 02:11:04 PM
I guess I can see your point on the aether thing. Isn't the Bell labs radio telescope discovery of the background noise from The Big Bang a similar example? Something ubiquitous that eventually had no other credible alternative explanation?

Yeah, but on a pretty short timescale. Penzias and Wilson had this brand new Bell Labs antenna that picked up the same amount of noise at a particular wavelength no matter what direction they looked. They did everything they could to remove sources of noise, which iirc involved scaring off some birds who had been crapping on the antenna with a shotgun. When they were super confident the instrument was working correctly and actually detecting something out in space, they called up a physicist, Robert Dicke, to ask if he had any idea what it might be. Dicke, who had been planning to build an antenna to search for the cosmic microwave background after he and Jim Peebles and others had made precise predictions about it, got off the phone, turned to his colleagues, and said, "Well boys, we've been scooped."
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on November 30, 2017, 05:44:59 PM
The Worst Theoretical Prediction in the History of Physics (http://alphacentauri2.info/index.php?topic=20238.msg108993#msg108993)
#Science #Cosmology #Astronomy #GeneralRelativity #CosmologicalConstant #QuantumFieldTheory
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on November 30, 2017, 05:47:44 PM
Heh. This is a story physicists like to tell.  ;)

If you look at quantum physics, it says that the vacuum of space should have energy itself. And since most of space is a vacuum, that would seem to work as a candidate for dark energy. But when you try to calculate how much energy might be in the vacuum (there's not necessarily a definitively correct way to do this), it comes out to be ~120 orders of magnitude (that is, a 1 followed by 120 0s) more powerful than the observed effect of dark energy. So that's a pretty bad prediction.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on November 30, 2017, 06:18:46 PM
(https://imgs.xkcd.com/comics/interferometry.png)
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on December 07, 2017, 08:16:34 PM
Since this is kind of the thread where I answer people's astronomy questions, here's a question I've got for all of you. I'm applying to grad school right now--a science writing master's program--and I need to get letters of recommendation. I've gotten 2 from the astronomy professors I TA'ed for last year, but I need a third one.

My initial thought (Option A) was to ask an astronomy professor I had a class with a couple years back who is in the department I work for now. I remember her praising my papers, and we're friendly and run into each other pretty frequently now. But one of my TA professors asked if I was getting a letter from the writing side of things, and the more I think about it the more that sounds like it might be a good idea. The problem is that my last class was a year ago and I was never super close with any instructor, either in the astronomy department or elsewhere. But there are a few candidates I've come up with.

(Option B) Fall 2016, I took a class on the philosophy of language that involved a lot of writing. That's the most recent class I've taken, so there's a better chance of the instructor remembering me and having positive things to say. Downside is he's just a grad student, and apparently having the Dr. before your name is a biiig plus for letters of recommendation.

(Option C) Spring 2016, philosophy of mathematics. That was a small class (~10 people) that involved a lot of writing and active discussion every class that I actually participated in. I think there's a good chance the instructor will remember me, but it was a year and a half ago. Upside is he's now a postdoc and can put Dr. in front of his name (but is no longer at the university).

(Option D) Also Spring 2016, literature of science and technology. A lot of writing that superficially sounds similar to what the grad program would be like (not really, because the instructor mostly had us write about post-modernism and globalism for some reason), and the instructor was quite complimentary of my writing. Con: larger class, not sure if he will remember me; still a PhD candidate.

Anybody have any thoughts or advice to offer? Monkeys.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on December 07, 2017, 09:06:47 PM
Not that I ever did that kind of application, but Option C sounds to me like it would stand out in a good way. Me reading it, I'd notice the Phd now somewhere else and conclude, either Lori is such a standout that he has a lasting contact with this guy, OR Lori is diligent enough to be able to get references from other places, not just the convenient undergrad ones.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on December 07, 2017, 11:30:08 PM
Yeah, that's what I'm leaning toward. Will have to see if I can find his new contact information...
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on December 11, 2017, 05:00:52 PM
Hey Lori - I had an idea for you.  You asked a few months ago about qualifications to be a science writer/popularizer.

-So, what if when I see a journal link in a science article, I post it, and you try writing it up.  You could even do easy and hard versions.  I have a journalism background, and would be glad to chip in on style, and I'm sure all of us would be glad to ask questions and give you a feel for what needs dwelling on and what doesn't - at lest for a somewhat science-literate audience most likely to read such things.

It would also generate blog articles, of course.

Here's two links on an astronomical topic...

http://iopscience.iop.org/article/10.3847/1538-4357/aa9789 (http://iopscience.iop.org/article/10.3847/1538-4357/aa9789)
http://aip.scitation.org/doi/full/10.1063/1.4964481 (http://aip.scitation.org/doi/full/10.1063/1.4964481)
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on December 11, 2017, 06:58:37 PM
That sounds like a good idea. It will have to wait a little bit, though. I need to be writing application essays for the grad program thing I'm applying to.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on December 20, 2017, 11:03:09 PM
[url]http://iopscience.iop.org/article/10.3847/1538-4357/aa9789[/url] ([url]http://iopscience.iop.org/article/10.3847/1538-4357/aa9789[/url])
[url]http://aip.scitation.org/doi/full/10.1063/1.4964481[/url] ([url]http://aip.scitation.org/doi/full/10.1063/1.4964481[/url])


Oh boy. So these papers deal with magnetohydrodynamics (MHD), which is a complicated field I know almost nothing about. With what I do know and can piece together from some digging, here's the story.

Directly observing or performing experiments on phenomena for which MHD is relevant is hard. MHD deals with the movement of electrically conductive fluids, so we're talking about the molten core of the Earth, or the plasma in the solar atmosphere, or the accretion disks of supermassive black holes. Because studying these directly is problematic, physicists have developed a lot of simplifying models using the equations of fluid dynamics and electromagnetism.

One explosive feature we see in this field is something called magnetic reconnection. Because you've got charged particles moving around in plasmas, you also have magnetic fields. Magnetic reconnection is a process by which energy stored in a magnetic field is released as heat or kinetic energy when the shape (topology) of the field changes in a dramatic way. Solar flares, for example, are very likely a result of reconnection, so understanding the process is important. These papers discuss problems with an older model of reconnection and the ways in which their newer model solves them.

In simplistic, ideal MHD, where there's no fluid viscosity or electrical resistivity or anything like that, plasmas will flow along magnetic field lines just like metal filings following field lines around a bar magnet. Even if there are shocks or waves in the plasma, the topology of the lines won't change and everything just keeps going. But we know that in real situations, when magnetic field lines get pushed around and tangled up, they can snap and form new lines. This is magnetic reconnection, and if it happens very rapidly (which seems to be the case), the particles following along with their lines suddenly jerk around and start colliding, and all that turmoil releases energy.

Because ideal MHD cannot account for this, physicists have developed models to explain the phenomenon. A classic one is the Sweet-Parker current sheet. So imagine you've got two magnetic field lines sitting parallel to each other but pointing in opposite directions.

S---------->N
N<----------S

The model says that electric current will start to flow in a thin sheet between the two field lines. But these current sheets are susceptible to tearing, because we're dealing with a very chaotic environment. When that happens, the sheet collapses and the magnetic field lines--brought closer together by the current sheet--can break and reconnect in a different orientation. (Below, the lines pinch off in the middle and turn around.)

S-----\ /---->N
N<---/ \------S

The problem is that on the scales of astrophysical phenomena (like solar flares), the Sweet-Parker model says magnetic reconnection should take weeks or months and be kind of a gradual thing, rather than the fast, explosive events we actually see. So a lot of work has been done trying to figure out how to make fast reconnection happen.

These two papers dig into the theoretical details of a current sheet model in which plasmoid instabilities cause sheets to collapse. Plasmoids are little magnetic bubbles of plasma that can form in a current sheet as it's growing. These isolated magnetic bundles separate chunks of the current sheet, leading to many smaller sheets connecting the two magnetic lines rather than one large one. The smaller sheets collapse more quickly, allowing fast reconnection and explosive energy release.

The big idea behind the model used in these papers is a least-time principle. Plasmoid instabilities initially grow at a linear rate. Eventually, the process stops being linear and gets weird. Their least-time principle argues that whichever plasmoid instabilities get through the linear phase of growth first will become dominant, and so its their properties which determine how the current sheet evolves and breaks down.

The big result from the theoretical work done in these papers is a set of scaling laws, which show how the properties of plasmoid instabilities change at different scales. Scaling laws in physics are very often power laws, which means that if you double x, the properties of x go like 2^n, where n is some constant power. Their results show that this is not the case for plasmoid instabilities and their scaling laws are more complicated, requiring different rules at different scales. One of the results to come out is that current sheets thin quickly, and this plays a big role in how plasmoid instabilities grow.

After detailing the scaling laws and factoring in things like viscosity and resistance, they show that magnetic reconnection can happen very quickly, on timescales comparable to what would be necessary for, say, solar flares.

There's plenty more work to be done here in terms of (a) adding in more variables to make the model more realistic and (b) testing the model in plasma physics experiments. You can do this on the ground, but you can also do this in satellites that park themselves in our magnetosphere and monitor activity to see if plasmoid instabilities really grow the way the model suggests.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on December 20, 2017, 11:42:23 PM
Ok.  Now, try to condense it to a 500-word Jack Horkheimer script, only less lamely unfunny.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on January 03, 2018, 01:45:23 AM
How goes the grad school application?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on January 03, 2018, 02:43:15 AM
Just waiting for my letters of recommendation to come in now. I have to send the whole thing in by January 15 and then wait until April 1 for a decision.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on February 22, 2018, 03:19:38 PM
Ah phooey. Didn't get in. Now to figure out what to do with my life again.
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on February 22, 2018, 04:11:43 PM
Become an electrical engineer. 

Rocket companies are ALWAYS hiring electrical engineers. 
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on February 22, 2018, 04:14:52 PM
Well my qualifications for that are... I understand the physics pretty well and played around with some oscilloscopes and circuit boards for a semester of E&M.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on February 22, 2018, 05:04:37 PM
As long as you know the basics of ;liftoff... :D
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on February 22, 2018, 06:31:58 PM
Well my qualifications for that are... I understand the physics pretty well and played around with some oscilloscopes and circuit boards for a semester of E&M.

I decided a long time ago maths is maths.  Yeah, one specialty uses a different set of equations more than another, but it's all math. 

Except finance.  I don't think they are using math anymore. 
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on February 24, 2018, 03:04:32 AM
Well my qualifications for that are... I understand the physics pretty well and played around with some oscilloscopes and circuit boards for a semester of E&M.

I decided a long time ago maths is maths.  Yeah, one specialty uses a different set of equations more than another, but it's all math. 

Except finance.  I don't think they are using math anymore.

I just read this to my wife ( CPA/ Chief Accounting Officer ) when she asked what I was laughing about. She chuckled and said "Creative Writing. Seriously, we use a lot of creative writing."
Title: Re: Astronomy/cosmology questions...
Post by: Geo on February 24, 2018, 06:09:13 PM
There's a difference between a CAO and CFO (Chief Financial Officer)?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on February 24, 2018, 06:30:39 PM
https://arxiv.org/abs/1801.01120
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on February 24, 2018, 10:12:22 PM
Is it cheating if I read the SciTech Daily article first?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on February 24, 2018, 10:54:34 PM
Only if you still write it up.

Honest.

(We've both let this slide lately [I wasn't entirely kidding about a short Horkheimer version], and really ought to dedicate a thread, since you need to write up science outside your expertise if that's a thing you fancy trying to make money at...  You're quite smart, even by the standards of this community, and clearly well-read; I think you could swing the archaeology papers, notwithstanding the difference in jargon and rigor.)
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on February 24, 2018, 11:46:42 PM
I did actually get started on a shorter version of the plasmoid instabilities write up but then got a nasty case of not-wanting-to-get-out-of-bed-itis. I'll see what I can do.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on February 25, 2018, 12:04:25 AM
I'm only beginning to recover from a winter mood, so you know I understand.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on February 25, 2018, 07:50:34 AM
Ah, winter mood. Nothing compared to post-vacation mood.

Seriously, here I was thinking I'd visited one of the coldest 'summer regions' on Earth only to sit out a very late freeze time in my own country.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on February 26, 2018, 07:46:55 PM
I've changed my mind.  It's nothing but clear that pro science writers read each other's stuff all the time.  Have a look at that SciTech Daily article and party on with your own bad self.
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on February 27, 2018, 01:29:25 PM
Well my qualifications for that are... I understand the physics pretty well and played around with some oscilloscopes and circuit boards for a semester of E&M.

I decided a long time ago maths is maths.  Yeah, one specialty uses a different set of equations more than another, but it's all math. 

Except finance.  I don't think they are using math anymore.

I just read this to my wife ( CPA/ Chief Accounting Officer ) when she asked what I was laughing about. She chuckled and said "Creative Writing. Seriously, we use a lot of creative writing."

I'll buy that.  Boeing once tried to train me to do some purchasing on the side.  I still haven't found anyone to explain to me how the $8 product I found locally was a 'worse deal' than the $52 same exact item they bought from New York.  I mean, I know the theory behind it in general, but it just left me convinced that the government budget could be cut in half by anyone with the least amount of common sense. 
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on February 27, 2018, 05:44:35 PM
https://arxiv.org/abs/1802.08257
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on February 27, 2018, 07:09:27 PM
I've changed my mind.  It's nothing but clear that pro science writers read each other's stuff all the time.  Have a look at that SciTech Daily article and party on with your own bad self.


So I didn't read that article specifically, but I have been following this story. Nevertheless, here's my take:

In the 1920s, Hubble famously discovered the expansion of the universe by looking at Cepheid variables in other galaxies. Cepheid variables are standard candles, which is what astronomers use to measure cosmic distances. Because a star that looks bright might be a close, dim star or a distant, luminous star, we need a way to independently determine how bright a star should be in order to figure out how far away it is. Cepheid variables serve as a standard candle because their brightness periodically pulsates and there is a correlation between the pulsation period and its average peak brightness. So the longer the period, the brighter a Cepheid should be, which means that if you find a dim, long period Cepheid, you know it must be very far away.

The tricky part is that in order to calibrate "very far away," you have to know the actual distances to some nearby Cepheids by some other method. This is the cosmic distance ladder, by which we climb one distance-measuring rung to reach the next. For the closest interstellar objects, we measure distance by "parallax," which in practice is a kind of vague term that corresponds to any method that uses a combination of time and geometry. The distances to the Cepheids Hubble used were actually determined via "statistical parallax," which is a little complicated and not central to this story. (See this (http://anomalous-readings.blogspot.com/2017/05/rungs-all-way-down.html) post if you want to get a better idea. Although I'm not super happy about how that one turned out.)

When you hear the term parallax, what probably springs to mind is what astronomers refer to as "stellar parallax," which is observing the apparent shift of a foreground star against background stars as the Earth moves around its orbit. Measure the position of a star. Wait half a year. Measure again. The greater the difference between the star's two apparent positions, the closer it is. This paper details a very precise set of stellar parallax observations made using the Hubble telescope. I'll talk about why these measurements are so good in a bit, but we're not quite done with Hubble the dude.

Hubble's discovery required accurate distance measurements and accurate spectroscopy. The faster a star is receding from you, the redder its spectrum will be due to the Doppler shift (redshift for astronomy). What Hubble found was a roughly linear relationship between distance and recession speed. A galaxy twice as far away as another will be receding at twice the speed. Combine this with some fancy math from general relativity and you can conclude that the universe is expanding and must have been smaller in the past. The expansion rate is now referred to as Hubble's constant. However, due to some systematic errors present at the time (for example, there were Cepheids that behaved differently from the rest, but no one knew it then), Hubble's estimate was an order of magnitude too high.

In the decades that followed, astronomers were able to get a much more accurate value for Hubble's constant and were also able to extend it out across the entire cosmos. They achieved this by finding more standard candles, the most important of which is type 1a supernovae. These work as standard candles out to much greater distances than Cepheids because they are extremely luminous and they have a fairly well understood peak luminosity based on underlying physics. Using these supernovae, astronomers were able to show that Hubble's constant is in fact pretty constant over long stretches of time and space. Cool.

So there are two reasons why the most recent Hubble observations are able to pin down a value for Hubble's constant with even less uncertainty. The first has to do with consistency. They measured the parallax of Milky Way Cepheid variables using the same Hubble camera that's been used to measure the brightness of extragalactic Cepheids. This means they can be very confident that discrepancies aren't just due to using different instruments.

Second, they're also using a relatively new technique for taking pictures with Hubble called spatial scanning photometry. Rather than just staring at a star and collecting its light over a period of time, they get Hubble to scan diagonally over it, leaving a star trail on the CCD and then adding up all the light from the trail. The advantage of this method is that you can collect a lot of light from a single source without saturating your pixels and you're not relying on one group of pixels to calculate the brightness of the star. You can average out the brightness across this diagonal pixel slash in a way that reduces the chance for error due to (essentially) imperfect calibration.

So the team got very precise measurements of the brightness and parallax of Milky Way Cepheid variables, which let them recalibrate the cosmic distance ladder all the way out to type 1a supernovae and come up with an even better measurement of Hubble's constant. Great. The reason this story is making headlines, however, is that it widens and solidifies the gap growing between this method of determining Hubble's constant and another method.

Let's flash back to Hubble the dude for a moment. He discovers the expansion of the universe, and theorists run with this idea and postulate a big bang. A big bang should leave behind observational evidence in the form of the cosmic microwave background, which formed when the universe cooled down enough so that electrons could calmly orbit protons and photons could stream outward without fear of hitting those electrons. Some of the static on your TV that nobody sees anymore because we've all gone digital is a result of CMB photons reuniting with matter for the first time in like 13.7 billion years, having cooled down to 2.7 kelvins.

But with very good satellites and other radio/microwave telescopes, we can detect much more than static in the CMB. There are tiny temperature fluctuations, some of them on large scales, others on small scales. You can plot all these variations as a power spectrum, which measures how strong your fluctuations are at particular sizes. The exact shape of this spectrum depends on a variety of factors, but cosmologists can model what it should look like using relatively simple physics.

One of the primary parameters influencing the CMB power spectrum is the ratio of matter and energy when the CMB formed. Before the CMB, matter and photons bounced around in a big sloshy mix that caused reverberations throughout the cosmos. Once the CMB formed, they separated and stopped influencing each other. The result is that the CMB power spectrum encodes the matter and energy waves that were most prominent at that last moment of scattering, so the ratio of matter to energy tells you what kind of waves you should get.

The big bang says the universe started out with more energy (from photons and neutrinos) than regular matter. However, as the universe expands, energy dilutes more quickly than matter (due to redshift), which means that at some point, matter becomes more dominant than energy. The ratio of matter to energy that you get from the CMB tells you when this happens, which tells you how quickly the universe is expanding, which gets you another estimate of Hubble's constant. (The difficult part is that many factors go into the CMB power spectrum, so this really gives you a range of acceptable values for the Hubble constant as those other parameters slide around.)

And the problem is that as more accurate maps of the CMB have been drawn (from WMAP and Planck), the value of Hubble's constant they're getting and the value coming from type 1a supernovae have stopped overlapping. The CMB gets you 67 km/s/Mpc, and this new paper's recalibration of Cepheid variables gets you 73 km/s/Mpc, and the uncertainties have shrunk enough that you can't just hope they're really the same value. So there's something important that cosmologists are missing. Thanks to efforts like this most recent paper, measurement error is probably not the answer. Maybe new physics? Maybe assumptions underlying one or both methods are wrong? No one is really sure yet. It's a pickle.

Wow that was way too long. I'll see if I can put together a shorter version later.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on February 27, 2018, 07:46:32 PM
Your language is good, but I'm going to need to teach you some news/journalism style.  You want to begin with a "lede", which is one sentence, concise as humanly possible without being misleadingly simple, with a summary of, and/or hook for, the article's idea(s).

Skimming the beginning, you need to say "astronomer Edwin Hubble" to avoid confusion with his eponymous space telescope.  At the mention of six months later for parallax. you probably ought to work in as briefly as possible that it's opposite side of orbit = greatest distance baseline.

I mean, in general, you want to cut where feasible, simplifying, but also idiot-proofing.

I'll try hard to give you an in-depth reading and a lot more feedback later today when I'm caught up on my daily routine.

Protip:  Always come up with a headline or two - not just for presentation here, but because even good editors sometimes come up with a head that misses the point and/or is a lame joke and/or chaps your butt some other way; it is standard practice to end you copy with some suggested headlines, which they may actually use instead of inventing something embarrassing.  Here, you'll want to bold your favorite at the top - but just as well get in the habit of putting any other head ideas at the bottom.

I should quote the journal link and these two posts to the dedicated thread, so we can go on from there there, shouldn't I?
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on April 28, 2018, 01:01:10 AM
Lori, I imagine almanac stuff is not really in your wheelhouse, but - can you speak to the impression I've gotten over a couple years of feeding cats at sunset that the time changes enormously faster near equinox than solstice?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on April 28, 2018, 01:54:16 AM
So are you referring to how fast the sun rises and sets? If so, then yes, it absolutely does so fastest at the equinoxes and slowest at solstices. At equinox, the run rises and sets exactly due east and west, so all of its (relative) motion is up and down. At other times, the sun's motion is at an angle, which means some component is not exactly up and down, so the rising and setting part is slower.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on April 28, 2018, 02:00:51 AM
I'm referring to how fast the length of the day changes.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on April 28, 2018, 02:08:21 AM
I was going to answer that question first but then for some reason thought you might be asking the question I answered, then decided to answer both, then realized that would be convoluted and bloated and just answered the one question.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on April 28, 2018, 02:11:39 AM
But again, yes, it changes fastest near equinox. If you think about this, it has to be the case. Just before winter solstice, the day is getting shorter each day. Just after solstice, it's getting longer. This can't be discontinuous, so the rate at which the amount of daylight changes has to go to 0 at the moment of solstice. The rest of the time it's going to be faster, with the fastest rates right in between the two solstices: the equinoxes.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on April 28, 2018, 02:14:02 AM
I thought it was something of the sort, but couldn't quite wrap my head until now.  Thanks, and thanks in advance from Momma.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on May 24, 2018, 07:08:32 PM
Okay. Stumbled across this cool looking Mars terraforming video.
https://www.facebook.com/ScienceNaturePage/videos/1332147706917484/UzpfSTExNzM2NjM0MzkzNTIxMzk6MTk4MTYzNzg3NTIyMTM1NA/ (https://www.facebook.com/ScienceNaturePage/videos/1332147706917484/UzpfSTExNzM2NjM0MzkzNTIxMzk6MTk4MTYzNzg3NTIyMTM1NA/)

This doesn't square with my concept of terraforming Mars. The usual explanation is that my concept of science is stuck in the Space Age.  Melting the icecaps would only result in two polar seas. Where are they getting the oxygen and hydrogen for oceans and atmosphere? Are they defrosting the perma-rust and then using plants to liberate the oxygen from the iron?

Don't get me wrong- I love the idea of terraforming Mars and always have, new worlds are full of possibility. But is this a possibility in want of commitment, or is it science fiction like the colonization project which hasn't worked out the critical problems yet?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 24, 2018, 07:26:38 PM
I'll watch the video and comment when I get home from work, but honestly I get all my knowledge of terraforming Mars from:

https://boardgamegeek.com/boardgame/167791/terraforming-mars
Title: Re: Astronomy/cosmology questions...
Post by: E_T on May 25, 2018, 12:36:19 AM
Okay. Stumbled across this cool looking Mars terraforming video.
https://www.facebook.com/ScienceNaturePage/videos/1332147706917484/UzpfSTExNzM2NjM0MzkzNTIxMzk6MTk4MTYzNzg3NTIyMTM1NA/ (https://www.facebook.com/ScienceNaturePage/videos/1332147706917484/UzpfSTExNzM2NjM0MzkzNTIxMzk6MTk4MTYzNzg3NTIyMTM1NA/)

This doesn't square with my concept of terraforming Mars. The usual explanation is that my concept of science is stuck in the Space Age.  Melting the icecaps would only result in two polar seas. Where are they getting the oxygen and hydrogen for oceans and atmosphere? Are they defrosting the perma-rust and then using plants to liberate the oxygen from the iron?

Don't get me wrong- I love the idea of terraforming Mars and always have, new worlds are full of possibility. But is this a possibility in want of commitment, or is it science fiction like the colonization project which hasn't worked out the critical problems yet?
Need a good Magnetic Field and Ozone layer so as to keep any real atmosphere that is released...  But it will last for a few millennium or so without...
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on May 25, 2018, 07:51:15 PM
Yeah, I know, I kind of buried the lede there. It's mostly a computer job. I'm working for my university, helping NASA organize and archive data on small solar system bodies.

But what about the new thing on the block, 2015 BZ509? (An asteroid in a retrograde co-orbital resonance with Jupiter, recently asserted to be of possible interstellar origin). NASA's site didn't return any results when I searched for it.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 25, 2018, 07:56:10 PM
I'll watch the video and comment when I get home from work...

I lied. Anywho, the problem with Mars is that it's dry and cold and has a thin wisp of an atmosphere. The bad news is there's no good way to directly combat either the dryness or the coldness.

If you melt the ice caps or bombard the planet with icy comets or setup an interstellar bucket brigade, the extremely low pressure means any liquid water more or less instantly boils away.

You also can't really increase the temperature because, well, what is it you're heating up? Not Mars itself--it's way too large. You just want a higher surface temperature, but there's barely anything on the surface to have a temperature.

The good news is both these problems can be solved by introducing an atmosphere. There is dry ice (frozen CO2) in the polar caps and probably some other greenhouse gases stuck in rocks. And the solar system is full of ammonia and CO2 and hydrocarbons that could be used to trap heat. Throw a whole lot of atmosphere onto the planet, trap heat, warm it up, melt ice, produce water vapor which is an extremely potent greenhouse gas, get yourself a nice positive feedback loop going on.

If you establish any kind of water cycle, the ice in the polar caps will eventually "fall" into the low-lying areas on Mars. (We see something similar happen on Mercury and Titan, for example.) There are questions about how much water is tucked away on Mars. May need to import more.

And Mars' lower gravity means you need a lot more atmosphere than that present on Earth to get the same surface pressure. And Mars' distance from the sun means it's just plain colder. May want to setup giant space mirrors to direct more light at the surface.

And yes, there's the problem that Mars' low gravity and lack of a magnetosphere means its more susceptible to atmospheric escape. Timescale on this is pretty long, but still something to worry about.

It's all pie in the sky right now. Transporting that much material through the solar system doesn't seem to be physically impossible, but we currently have no experience with any of that. How do you build a planet-wide magnetic field? How do you create a biosphere from scratch? How do you make sure you don't accidentally create Venus? No solid answers to those questions right now.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 25, 2018, 08:03:15 PM
But what about the new thing on the block, 2015 BZ509? (An asteroid in a retrograde co-orbital resonance with Jupiter, recently asserted to be of possible interstellar origin). NASA's site didn't return any results when I searched for it.

You can either go to JPL Horizons (https://ssd.jpl.nasa.gov/horizons.cgi) and hit change Target Body or the Minor Planet Center (https://www.minorplanetcenter.net/iau/MPEph/MPEph.html) and search there. This will mostly just bring up the Ephemeris data--position, speed, distance at certain times. Anything specific you want to know?

For what I do specifically, I help with the Planetary Data System (PDS) archive. We archive NASA mission data and other people who make proposals to store stuff with us. So we don't just have a generic listing of small bodies unless there's been some NASA-funded mission to look at some objects.
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on May 25, 2018, 11:21:05 PM
Not specifically, since it seems there's a number of speculative theories and seemingly a need for better orbital data and extensive modeling. Tangentially, do you think Planet Nine exists?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 26, 2018, 12:10:31 AM
I'm withholding judgment. Not a lot of evidence yet (a handful of KBOs with weird orbits), and not convinced there aren't observational biases in our detection so far (such that we're just seeing the weird ones right now but the population is distributed more or less randomly). Plus there are alternative theories, such as: https://www.youtube.com/watch?v=YW0Zb5gY0HA (https://www.youtube.com/watch?v=YW0Zb5gY0HA)

(Wow I could not figure out how to embed...)
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on May 29, 2018, 04:46:57 PM
So conservation of angular momentum is a variation of voodoo magic. Got it.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on May 29, 2018, 06:01:53 PM
I'll watch the video and comment when I get home from work...

I lied. Anywho, the problem with Mars is that it's dry and cold and has a thin wisp of an atmosphere. The bad news is there's no good way to directly combat either the dryness or the coldness.

If you melt the ice caps or bombard the planet with icy comets or setup an interstellar bucket brigade, the extremely low pressure means any liquid water more or less instantly boils away.

You also can't really increase the temperature because, well, what is it you're heating up? Not Mars itself--it's way too large. You just want a higher surface temperature, but there's barely anything on the surface to have a temperature.

The good news is both these problems can be solved by introducing an atmosphere. There is dry ice (frozen CO2) in the polar caps and probably some other greenhouse gases stuck in rocks. And the solar system is full of ammonia and CO2 and hydrocarbons that could be used to trap heat. Throw a whole lot of atmosphere onto the planet, trap heat, warm it up, melt ice, produce water vapor which is an extremely potent greenhouse gas, get yourself a nice positive feedback loop going on.

If you establish any kind of water cycle, the ice in the polar caps will eventually "fall" into the low-lying areas on Mars. (We see something similar happen on Mercury and Titan, for example.) There are questions about how much water is tucked away on Mars. May need to import more.

And Mars' lower gravity means you need a lot more atmosphere than that present on Earth to get the same surface pressure. And Mars' distance from the sun means it's just plain colder. May want to setup giant space mirrors to direct more light at the surface.

And yes, there's the problem that Mars' low gravity and lack of a magnetosphere means its more susceptible to atmospheric escape. Timescale on this is pretty long, but still something to worry about.

It's all pie in the sky right now. Transporting that much material through the solar system doesn't seem to be physically impossible, but we currently have no experience with any of that. How do you build a planet-wide magnetic field? How do you create a biosphere from scratch? How do you make sure you don't accidentally create Venus? No solid answers to those questions right now.

Thank you. So the practical approach at this time would still be the Total Recall method - do whatever you do underground?

Okay, that raises another stupid series of questions. I presumed atmosphere retention was strictly a function of gravity, but if it isn't does that mean that the less massive Mars requires a stronger magnetic field to retain an atmosphere? If all planets don't have magnetic fields, why do some have them and others not? The dynamo effect of a molten core? The  massive presence of nickel and iron ? A radiation belt ? Or is that a side effect of a magnetic field?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 29, 2018, 07:46:45 PM
Okay, that raises another stupid series of questions. I presumed atmosphere retention was strictly a function of gravity, but if it isn't does that mean that the less massive Mars requires a stronger magnetic field to retain an atmosphere?

In the absence of solar wind, particles in the atmosphere escape when they are moving too fast (high temperature) and not being held on to tightly (low gravity). The solar wind is a stream of high-energy particles that can knock bits of atmosphere away. Weaker gravity means particles are more easily knocked loose, but the solar wind is weaker out at Mars than at Earth. Not sure how this all works out.

Quote
If all planets don't have magnetic fields, why do some have them and others not? The dynamo effect of a molten core? The  massive presence of nickel and iron ? A radiation belt ? Or is that a side effect of a magnetic field?

Yep. In general, bigger planet = hotter core = dynamo effect. Some gas giant moons gets protection from their planets. Jupiter itself has a very strong magnetic field which probably comes from the super weird and poorly understood "metallic hydrogen" in the core. So classical metals not strictly necessary. Smaller planets (Mars, Mercury) have cooled down and don't have magnetic fields anymore.

But neither does Venus, even though it's the same size as us. Why? Prooobably because it spins slowly. Jury's still out on this. We can say "dynamo" and that conjures an image of some simple 19th century device that we must surely understand completely by now, but planets are big and complicated.
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on May 29, 2018, 08:16:44 PM

Thank you. So the practical approach at this time would still be the Total Recall method - do whatever you do underground?


But boring. I like the giant magnetic balloon(s) (https://phys.org/news/2017-03-nasa-magnetic-shield-mars-atmosphere.html).
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 30, 2018, 12:39:32 PM
So conservation of angular momentum is a variation of voodoo magic. Got it.

Well yeah.

https://www.youtube.com/watch?v=r__nGqGpTD8 (https://www.youtube.com/watch?v=r__nGqGpTD8)
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on May 30, 2018, 11:38:08 PM

Thank you. So the practical approach at this time would still be the Total Recall method - do whatever you do underground?


But boring. I like the giant magnetic balloon(s) (https://phys.org/news/2017-03-nasa-magnetic-shield-mars-atmosphere.html).

That's a cool idea, but how much energy does it take to make a planetary scale magnetic field?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 31, 2018, 03:36:15 PM
Alright, so here's a really rough estimate. If the magnetic field is roughly the size of Mars + decent Martian atmosphere, and the strength is the same as Earth's (and uniform all the way through, which is probably a very bad assumption), and Mars is actually empty space... then you've got ~200 million gigajoules of energy stored in the field. Mars is really iron+nickel+rock, all of which are better at holding magnetic fields, so the answer may be lower by 2 or 3 orders of magnitude.

The largest nuclear plant in the US operates at ~4 Gigawatts, so you need to commandeer its output for a year and a half to produce your magnetic field. But if you do need less because you're dealing with the actual composition of Mars and not a vacuum, we're talking at most just a few days of that plant's output. It's honestly not an astronomical sum because Earth's magnetic field is in truth very weak (~50 microteslas, compared to the 5 milliteslas of a refrigerator magnet). It's only a lot because it's a huge volume of space.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on May 31, 2018, 06:14:10 PM
Alright, so here's a really rough estimate. If the magnetic field is roughly the size of Mars + decent Martian atmosphere, and the strength is the same as Earth's (and uniform all the way through, which is probably a very bad assumption), and Mars is actually empty space... then you've got ~200 million gigajoules of energy stored in the field. Mars is really iron+nickel+rock, all of which are better at holding magnetic fields, so the answer may be lower by 2 or 3 orders of magnitude.

The largest nuclear plant in the US operates at ~4 Gigawatts, so you need to commander its output for a year and a half to produce your magnetic field. But if you do need less because you're dealing with the actual composition of Mars and not a vacuum, we're talking at most just a few days of that plant's output. It's honestly not an astronomical sum because Earth's magnetic field is in truth very weak (~50 microteslas, compared to the 5 milliteslas of a refrigerator magnet). It's only a lot because it's a huge volume of space.

Thanks, I didn't mean to make you do so much math.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on May 31, 2018, 06:31:50 PM
I like math. ;)

Plus this was mostly just back of the envelope algebra. If I wanted to be semi-rigorous I would have integrated the magnetic field strength as a function of radius and maybe not treated the composition issue as just dropping a few zeros.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on August 28, 2018, 03:44:59 AM
Lori:  a bit of Star Trek universe fanwank I came up with and posted five years ago.  I'm interested in your opinion of the likelihood of the physics, proceeding from the assumptions...

Well, it starts with the plainly observable fact that everyone's artificial gravity is insanely reliable.
I conclude this:  in the ST universe, there's stuff about how gravity works that was discovered by the mid 90's.  Khan's ship had artificial gravity, and it wasn't spinning or accelerating.  So there's a way to make, dunno, a gravity deck plating cheaply that works for a very long time with little or no power input.  Every race discovers this application of the law of gravity pretty soon after they go into space.  The same, or similar, techniques make for a nifty non-reaction gravity drive, which Starfleet calls "impulse".  A slightly more sophisticated application involving the interaction of fields from two gravity generators distorts warps space-time and makes for a nifty FTL drive.  Thus, everyone and his mother has a FTL starship with two drive pylons of some sort.  Both types of drive take a lot more juice then the deck plates because the gravity fields, by the nature of the thing, are not static, but have to expand and contract and vary in intensity.  That Warp is probably by an order of magnitude more power-hungry than Impulse naturally follows.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 28, 2018, 06:11:36 PM
Hey BU!

So what we know about gravity is that it propagates outward radially and that it's very weak. The first part is tricky, because each deck on a starship is at 1 gee and so are the Jefferies tubes. So you need to make sure the artificial gravity on deck 1 doesn't bleed over onto deck 2, which means you need to be able to sharply reconfigure the field across short distances. Hard to imagine that not requiring a lot of energy.

Gravity being weak means, traditionally, you need an entire planet to get a reasonable amount of it. You need less than a planet if you're much closer to the source of gravity, but still on the order of, like, a small moon. But if you know some extra cool facts about gravity, like, say, how to generate gravitons, maybe you don't need all that mass.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on August 28, 2018, 06:19:26 PM
Oh, the way the artificial gravity works is bull, and nothing but -though it has to be low/no power, or they'd lose gravity in emergencies roughly every episode- but is the drive speculation worth anything?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 28, 2018, 06:56:42 PM
Well, depends on whether or not you're obeying Newton's third law/conserving momentum. If you can just randomly generate a gravitational field in space, then sure, maybe you won't run into any problems with Newton. But if impulse relies on a gravity generator producing thrust somehow, then your momentum needs to come from somewhere.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on August 28, 2018, 09:14:54 PM
But if impulse relies on a gravity generator producing thrust somehow, then your momentum needs to come from somewhere.

Quantum Space Foam!
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on August 29, 2018, 02:32:15 AM
-though it has to be low/no power, or they'd lose gravity in emergencies roughly every episode

You sure?  I was under the impression (not sure where not really a trek tech guy) the deflector dish was constantly channeling tremendous power just to keep dust from punching holes in the ship.  I haven't really seen it FAIL either.  In fact, you generally see life support fail before the deflector. 

Which...how DOES the deflector...uh, deflect?  Is IT directed gravity?  Fits with the tractor/repel beam it shoots out too...
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on August 29, 2018, 03:47:25 AM
Let me think about it a while, and see if I can come up with some outrageous bull that makes sense...
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on August 29, 2018, 12:27:09 PM
I'm pretty sure I remember a ship losing gravity in a movie I didn't finish.  Maybe it has a clue how that happened? 
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on August 29, 2018, 01:21:06 PM
The most common system to go offline on a starship is the inertial dampers. But they never go completely offline--just like 3% offline--because otherwise you'd need new characters next week.
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on August 29, 2018, 02:22:48 PM
From a Nasa article on trek science re: anti gravity. 
Quote
Try a web search for "levitating frog" to see how it's done


That lead me here: 

! No longer available (http://www.youtube.com/watch?v=ZLkP6S6mKsY#)

That lead me to some scholarly articles that they have produced 10+G with diamagnetism in extremely small scale experiments on single cell organisms.     

So, theoretically possible but stupidly insane power requirements, and a host of practical challenges to make it happen.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on August 29, 2018, 07:45:17 PM
I am out of my league in this astrophysics and rocket sciences, so I probably don't have anything to contribute. My guess is that said gravity deck tech is self contained. It meets the insane power requirements by being a sort of plug-in car system that gets recharged at star base
 12 or something.
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on August 29, 2018, 08:15:31 PM
Well, you're running a matter/antimatter reactor on the ship anyway, I don't know that power is necessarily a problem for the trek ships at that level so much as it would be for us today. 
Title: Re: Astronomy/cosmology questions...
Post by: Geo on August 30, 2018, 07:29:43 AM
Has to be some sort of self-contained or at the very least rechargeable system, otherwise the gravity would falter for sure each time the warp core is ejected. ;lol
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on August 30, 2018, 02:59:56 PM
Has to be some sort of self-contained or at the very least rechargeable system, otherwise the gravity would falter for sure each time the warp core is ejected. ;lol

I don't see why some kind of storage system built in, recharged by the warp core is out of the question. 

Only challenge I really see is TNG saucer seperation, I don't think the saucer had a warp core? 

Maybe it runs off the impulse fusion reactors? 
Title: Re: Astronomy/cosmology questions...
Post by: E_T on August 30, 2018, 07:25:30 PM
Auxiliary Power...
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on November 16, 2018, 05:51:16 AM
Okay, here's a new one for me- DARK FLOW
I was following some links and found myself here-  https://www.newscientist.com/article/mg20327246.000-13-more-things-dark-flow/ (https://www.newscientist.com/article/mg20327246.000-13-more-things-dark-flow/)

Could you illuminate the subject for me?
Title: Re: Astronomy/cosmology questions...
Post by: Geo on November 16, 2018, 12:08:51 PM
Sure! :link: (https://en.wikipedia.org/wiki/Great_Attractor)
Title: Re: Astronomy/cosmology questions...
Post by: E_T on November 17, 2018, 02:40:03 AM
Just watched something about the (relatively) recent discovery of the "super" Crater in Northern Greenland.  Some of the hypothesis have the impact around sometime during the last major Ice-age and that the ice sheet was likely much thicker at the time.

Granted, we do have a fairly good understanding of impact energies when hitting water as well as dry land (so as to create a crater of x size).  But what about when Ice is involved, when you take into account the latent heat quotient of not just one phase change (water to vapor) but also the second phase change (ice to water) for all that Ice.

How much would that change (or muddy up if you will) the calculations of the probable size and energy of the impacting object?

And, there have been questions about ejectra from the impact (or lack there of, but most could be currently under existing ice - some conjectures about side glance hit, but still), would the rapid melt/vaporization have any possible effect of how that might get distributed?
Title: Re: Astronomy/cosmology questions...
Post by: Geo on November 18, 2018, 05:27:30 PM
And, there have been questions about ejectra from the impact (or lack there of, but most could be currently under existing ice - some conjectures about side glance hit, but still), would the rapid melt/vaporization have any possible effect of how that might get distributed?

IIRC (the article mentioned it I think), the courtyard meteor which gave the researchers the idea of looking for impact signs in this location is a part of the ejecta.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on November 19, 2018, 06:49:32 PM
How much would that change (or muddy up if you will) the calculations of the probable size and energy of the impacting object?

Quite a bit, it would appear. The estimate given for energy/mass/speed of the impactor is based purely on the size of the crater. But if you dig into the paper, the authors acknowledge:

Quote
If ice was present and its thickness was comparable to the impactor’s diameter, then a more energetic projectile is required to produce a crater of the observed size, and the fraction of non-ice debris in the ejecta would be smaller than if the impact hit ice-free land (19).

And 19 is a reference to another paper modeling crater formation in icy layers on Mars. The abstract says:

Quote
The presence of an icy layer significantly modifies the cratering mechanics. Observable features demonstrated by the modeling include variations in crater morphometry (depth and rim height) and icy infill of the crater floor during the late stages of crater formation. In addition, an icy layer modifies the velocities, angles, and volumes of ejecta, leading to deviations of ejecta blanket thickness from the predicted power law. The dramatic changes in crater excavation are a result of both the shock impedance and the strength mismatch between layers of icy and rocky materials.

So... given that the crater they found looks pretty standard and they didn't see ejecta in the nearby ice, I'm leaning toward there not having been ice at the time. /me shrugs.
Title: Re: Astronomy/cosmology questions...
Post by: ColdWizard on December 06, 2018, 05:34:35 PM
If dark matter and dark energy are negative mass fluid and the fluid is continuously created, where does it come from?
Title: Re: Astronomy/cosmology questions...
Post by: Geo on December 06, 2018, 11:00:10 PM
If dark matter and dark energy are negative mass fluid and the fluid is continuously created, where does it come from?

Black holes!
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on December 07, 2018, 02:13:14 PM
Here's my go to wet blanket physicist on the negative mass fluid thing:

http://backreaction.blogspot.com/2018/12/no-negative-masses-have-not.html (http://backreaction.blogspot.com/2018/12/no-negative-masses-have-not.html)

She is not exactly complimentary. On the "where does it come from" question, she says:

Quote
Farnes also introduces a creation term for the negative masses so he gets something akin dark energy. A creation term is basically a magic fix by which you can explain everything and anything. Once you have that, you can either go and postulate an equation of motion that is consistent with the constant creation (or whatever else you want), or you don’t, in which case you just violate energy conservation. Either way, it doesn’t explain anything. And if you are okay with introducing fancy fluids with uncommon equations of motion you may as well stick with dark energy and dark matter.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on December 07, 2018, 05:13:56 PM
Every theory has to start at square one.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on December 07, 2018, 07:51:23 PM
Right, but we're not at square one here. As she points out in her post, she and many other experts in GR have played with the idea of negative mass/energy before. The theories haven't gained much traction because problems arise when you try to reconcile them with general relativity. This guy hasn't really addressed those previously explicated problems, so there's not a great reason to take his theory seriously.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on December 07, 2018, 10:18:05 PM
Oh, I don't take this theory seriously at all.
The negative repellant thing sounded to good to be true. One of my thoughts was that it could allow a sort of hyperspace travel.
Hence my black hole comment a couple posts ago, since they so to speak suck matter in.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on January 02, 2019, 02:29:56 AM
Brian May - New Horizons (Ultima Thule Mix) [Official Music Video] (http://www.youtube.com/watch?v=j3Jm5POCAj8#)
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on January 03, 2019, 02:18:43 PM
So...what the hell is up with Ultima Thule? 

I can't find much on a cursory glance, and all the news is so excited about the blurry snowman photo.  Are we still crunching data?  Are we still waiting for pics of it closer? 

You can't tell me the probe that sent back high def pics of Pluto can only manage a pixellated snowman here.  Or someone really blew the calculations and should have gotten it closer/activated the camera sooner/later/longer. 
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on January 03, 2019, 04:13:45 PM
If you'll remember, it took awhile to get high resolution images of Pluto, too. The downlink to the Deep Space Network is 500 bits/second, and it's expected to take 20 months for all the data to be transmitted. The snowman photos we've seen so far are still slightly pre-closest approach.

But this was a harder flyby than Pluto. The big constraint is that MU69 is much dimmer than Pluto (smaller, farther from the sun), so New Horizons had to get much closer to get good photos (the camera was designed for Pluto). On top of that, there's the complication that because we knew so little about the KBO going in, pinpointing its exact position for navigation was harder.

From what I've seen, though, all the telemetry and diagnostics look good and the team absolutely expects there are much higher resolution pictures in the pipeline. iirc, the best images should be 30 meters/pixel, with the object being 30 km long.
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on January 03, 2019, 05:05:58 PM
So shitty reporting (or possibly just bad on the PR team).  All the reports I've seen are in past tense, acting like that was it.  I knew that couldn't possibly be right unless something was wrong/somethone screwed up.  Need to highlight much better stuff coming down the line. 
Title: Re: Astronomy/cosmology questions...
Post by: E_T on January 03, 2019, 05:37:18 PM
Yeah, they should at least mention that there is more queued up and will be seen sometime soon.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on January 03, 2019, 05:38:43 PM
Well I'll tell you there is another press conference today on the latest batch of data, which should be composition information from a different (non-imaging) instrument.
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on January 03, 2019, 05:49:20 PM
compare/contrast with the news releases from Ceres. 

Granted, we don't have the 'what is the spot' mystery, but it was clear from that first image we were going to be getting a stream of info for weeks. 

Here the reports are 'we flew by yesterday, here's the pic'.  No promise of further insights.  Starting to think this is bad PR more than bad reporting.  (Something NASA has occasionally had problems with)
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on January 03, 2019, 05:59:58 PM
Yeah, with Ceres, Dawn was in orbit and still pretty close to earth, so it was understood to be an ongoing investigation with periodic updates.

I will say that in this case, while two of the institutions involved with the flyby are non-governmental (APL and SwRI), NASA is one of the currently furloughed agencies. That doesn't apply to mission operations people, but it does apply to press officers. /me shrugs
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on January 03, 2019, 06:15:44 PM
Good point, didn't think about that bit.  It does seem APL is attempting to handle most the PR stuff and look a bit out of their depth. 

I pulled up the probe design for giggles. 

So, the images we have are from LORRI(navigation camera), this is why they suck so bad.  We also have strong indications they fired up ALICE to determine the composition, but I haven't heard of any of the other pieces of equipment even firing up.  Do we know if the other suite of instruments even recorded?  RALPH is the pics the public would want to see, but is among the more energy intensive instruments on the thing, and is oriented completely differently than LORRI, so would have had to have passed to the 'right' of the LORRI images to get a shot...but Alice would also be able to record on that side.  REX, PEPSSI and SWAP could be interesting scientifically, but not so much to the general public, and I believe they might have had to choose between ALICE or PEPSSI for a flyby.   
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on January 03, 2019, 06:46:34 PM
Take a look at these two papers for details on the planned encounter with MU69.

https://arxiv.org/ftp/arxiv/papers/1806/1806.08393.pdf

https://arxiv.org/ftp/arxiv/papers/1808/1808.02118.pdf

Short answer is, yes, they were trying to use all available instruments (and the first bit of info they got post-flyby said they had collected as much data as they expected to).
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on January 03, 2019, 09:44:27 PM
Looks like Ralph's IR imager is running for a lot of the flyby, but it's only got a couple opportunities to take the HD pics.  I suspect they'll use those snapshots more as a color check to process the IR data, so we might eventually get some nifty pics. 

Today's conference looks like it was a 3d glasses version from Lorri.   :-\
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on January 03, 2019, 10:10:01 PM
Yeah, was disappointed by that presser. Yesterday they said we should get composition data today, but instead they mostly just talked about what they didn't find and then showed off the 3d stuff. Not sure what that means, exactly.

But on the neat side, the younger woman on that panel, Silvia, is a former colleague of mine. Among other things, we were both involved with archiving the Pluto flyby data. But then around this time last year she got a job at SwRI as a scientist on the New Horizons team.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on January 03, 2019, 11:14:32 PM
Yeah, was disappointed by that presser. Yesterday they said we should get composition data today, but instead they mostly just talked about what they didn't find and then showed off the 3d stuff. Not sure what that means, exactly.

But on the neat side, the younger woman on that panel, Silvia, is a former colleague of mine. Among other things, we were both involved with archiving the Pluto flyby data. But then around this time last year she got a job at SwRI as a scientist on the New Horizons team.

So, are you going to call her and congratulate her?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on January 04, 2019, 02:08:56 PM
Heh, that's not really my thing.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on January 04, 2019, 07:58:06 PM
Heh, that's not really my thing.


I thought that using that excuse would be an opening for asking a couple of interesting questions. Or, you could wait for the shutdown to be over to get your answers. Trump's rambling on about how he's willing to let it continue for years.


Regardless, I hope that 2019 is your best year ever.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on January 04, 2019, 08:38:47 PM
...to get your answers.

Well, as I said, my group is involved with the archival effort for New Horizons data. So I do have some contacts. But, well... :-X

Quote
Regardless, I hope that 2019 is your best year ever.

Thanks! I got a promotion and retroactive raise at the end of the year, so I'm hoping to move into my own apartment (rather than living with stranger roommates) some time this spring.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on January 05, 2019, 09:27:38 AM
...to get your answers.

Well, as I said, my group is involved with the archival effort for New Horizons data. So I do have some contacts. But, well... :-X

Piffle, if press leaks in DC are tolerated, why wouldn't a mere bureau leak be overlooked. ;)

A more serious question. If your group is solely responsible for the archival of one probe, does that mean that each and every NASA probe outthere winds up with its own group of people classifying its data?
And how does that work with flight crews? Does every probe has its own crew looking at telemetry as it comes in, or did for example (mostly) the same people deal with Deep Horizons during its Pluto flyby and with Dawn during its Ceres orbital program? Not to mention for instance the Juno probe?
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on January 05, 2019, 07:46:05 PM
So, a little less vaguely, NASA's planetary science missions are archived by the Planetary Data System. The PDS is divided up into separate nodes that specialize in particular disciplines of planetary science. I work for the Small Bodies Node, which is operated out of the University of Maryland. (All the nodes are semi-independent groups that are sometimes only loosely affiliated with NASA itself.) Small Bodies includes comets, asteroids, and interplanetary dust. So that's New Horizons but also stuff like Dawn. Cassini, which just ended its Saturn mission, is archived at the Ring-Moon Systems node. And so on.

Every individual mission has its own personnel, because the way these missions get funded is that some researcher (or group of scientists) gets awarded a grant through some part of NASA (or the NSF, or whatever), and then a team is assembled with that grant money to work on that mission. How deeply involved NASA is in the mission itself varies widely depending on the scope of the mission. It gets complicated very quickly. But team members are usually working on other projects at the same time, because to make a living they're probably securing funds from multiple different grants simultaneously.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on January 06, 2019, 04:09:14 AM
Thanks! I got a promotion and retroactive raise at the end of the year, so I'm hoping to move into my own apartment (rather than living with stranger roommates) some time this spring.


That's great news. Maybe someday you can get a Space Force Commission and double dip.
Title: Re: Astronomy/cosmology questions...
Post by: Geo on January 06, 2019, 04:37:15 AM
Thanks! I got a promotion and retroactive raise at the end of the year, so I'm hoping to move into my own apartment (rather than living with stranger roommates) some time this spring.


That's great news. Maybe someday you can get a Space Force Commission and double dip.

Good for you. :b
Does that mean you'll have space for a balcony telescope then? :D
And thanks for the response. In a sense I suppose its good you don't work for NASA directly because of the current government shutdown.
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on January 06, 2019, 05:33:34 PM
https://www.space.com/42903-new-horizons-ultima-thule-flyby-data-intermission.html (https://www.space.com/42903-new-horizons-ultima-thule-flyby-data-intermission.html)
https://www.space.com/42903-new-horizons-ultima-thule-flyby-data-intermission.html (https://www.space.com/42903-new-horizons-ultima-thule-flyby-data-intermission.html)

Quote
All told, it will take about 20 months for all the data currently trapped on the probe to be sent back down to Earth. That data includes "literally hundreds of images and spectra and other data types," Stern promised.

Gonna be a while before we get the high res pics.  Kinda makes me wonder if they shouldn't have held onto the news for a while so they had a more steady stream of info. 
Title: Re: Astronomy/cosmology questions...
Post by: Geo on January 06, 2019, 06:06:25 PM
https://www.space.com/42903-new-horizons-ultima-thule-flyby-data-intermission.html (https://www.space.com/42903-new-horizons-ultima-thule-flyby-data-intermission.html)
https://www.space.com/42903-new-horizons-ultima-thule-flyby-data-intermission.html (https://www.space.com/42903-new-horizons-ultima-thule-flyby-data-intermission.html)

Quote
All told, it will take about 20 months for all the data currently trapped on the probe to be sent back down to Earth. That data includes "literally hundreds of images and spectra and other data types," Stern promised.

Gonna be a while before we get the high res pics.  Kinda makes me wonder if they shouldn't have held onto the news for a while so they had a more steady stream of info.

Instant gratification, UnO, instant gratification. ;)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on January 21, 2019, 07:16:32 PM
Am I the only one who had good seeing for the eclipse?
Title: Re: Astronomy/cosmology questions...
Post by: Geo on January 21, 2019, 08:54:17 PM
Am I the only one who had good seeing for the eclipse?

't Was too frosty this mornin' to have time lookin' at it.
Needed to clean the windscreen and be on the road to work. Only saw the last phase through the canteen windows during mornin' break.

In any case, it must've been pretty dark during full eclipse. Didn't notice the Moon at all during my commute.
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on January 21, 2019, 08:57:50 PM
I had a good view up till about 3/4.  But between the pollution and the thin clouds could barely see the actual eclipse. Too bad, was trying to get Clarence a workout.   

(https://scontent-dfw5-1.xx.fbcdn.net/v/t1.0-9/49319533_2261999130500137_7987185800871673856_n.jpg?_nc_cat=107&_nc_ht=scontent-dfw5-1.xx&oh=f47188065769c20ed252ed0a6db16d19&oe=5CFAFEEC)
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on January 21, 2019, 09:56:49 PM
The half hour between 3/4 and total DID make a huge difference in how dark it was outside.

We could have done without the slight wind, too - felt like I was gonna die, which sorta harmed my viewing enjoyment.
Title: Re: Astronomy/cosmology questions...
Post by: E_T on January 21, 2019, 11:00:13 PM
There was an eclipse and I missed it?  Granted, it was cold but could have seen it fairly well as we didn't have too much cloud cover last night...
Title: Re: Astronomy/cosmology questions...
Post by: Elok on January 22, 2019, 02:39:19 AM
Am I the only one who had good seeing for the eclipse?
My wife and elder son stayed up to watch it together.  Laz said it wasn't worth staying up so late, but he spent the whole time reading, which he would do every night if we let him.
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on January 22, 2019, 04:11:27 AM
That's just what I'm about to do, until I fall asleep.
Title: Re: Astronomy/cosmology questions...
Post by: Rusty Edge on January 22, 2019, 05:27:15 AM
It was overcast, and about 3 degrees. I couldn't tell where the moon was & I went to bed. The background light here usually washes out most of the stargazing.
Title: Re: Astronomy/cosmology questions...
Post by: Lorizael on January 22, 2019, 02:19:11 PM
I went out and back in periodically during the eclipse, because it was extremely cold and windy here. Didn't get any pictures, because I didn't want to fiddle around with gadgets. Just watched through my binoculars. Nice shot, Uno.
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on January 22, 2019, 03:44:48 PM
Nice shot, Uno.

Yeah, Clarence has really surprised me with it's moon pics. 

Makes me want to look into getting the telescope mount and trying to find a cable for my telescope again.  (it needs a serious update as it doesn't track objects properly anymore, so is fairly useless finding much beyond mars or so.  But proprietary cable interface with computer didn't come with and isn't available now.  Older telescope bought used) 
Title: Re: Astronomy/cosmology questions...
Post by: E_T on January 23, 2019, 03:47:29 PM
A Space Rock Hit The Moon During The Eclipse https://www.youtube.com/watch?v=Smp7TqccTpY (https://www.youtube.com/watch?v=Smp7TqccTpY)

Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on March 04, 2019, 09:59:10 PM
Could y'all edumacate me about why they don't wrap something like a Faraday cage -or maybe just a silvered mylar envelope- around the ISS -or one whole module, anyway- and run a current through it for a radiation shield?  Same for traveling crew capsules, though I see that's a considerably greater engineering challenge...

Like, the big short-term threat is solar flares, right?  And that's a particle radiation problem, right?  And a large/intense enough magnetic field will handle particle radiation -if not the x, gamma, etc., wave radiation- nicely.  So, this is an obvious enough thing that I figure, with fair confidence, that there were pretty definitive theoretical/engineering studies done by the time I was born in the mid-sixties, and either the power requirements are prohibitive to do that for three days of so, or there's too much wave radiation in a flare - or both.  Help me out here, if you can...
Title: Re: Astronomy/cosmology questions...
Post by: Geo on March 05, 2019, 07:46:57 AM
I'd say the ISS doesn't have power to spare for such a project?

Besides, isn't the ISS still within Earth's magnetic field? Its barely 500 clicks up...
Title: Re: Astronomy/cosmology questions...
Post by: Buster's Uncle on March 05, 2019, 07:45:01 PM
Yes, it's inside the Van Allen belts.

Still...
Title: Re: Astronomy/cosmology questions...
Post by: Elok on March 06, 2019, 03:26:05 AM
So, probably question for Lori specifically: is the Seveneves scenario plausible, in the sense that if something fragged the moon, the pieces would stay in close proximity for a bit banging into each other, but gradually break into smaller and smaller pieces?  I always found that really hard to visualize.  Threw this question out to the Slate Star Codex hivemind, but didn't get a complete answer.
Title: Re: Astronomy/cosmology questions...
Post by: Unorthodox on March 07, 2019, 12:27:45 PM
If I understand the synopsis correctly: the moon breaks into several large chunks that stay where the moon was, I'd rate it as rather impractical but technically plausible. 

Anything that would destroy the moon would most likely severely impact it's orbit.  Given some theoretical internal break up, it's theoretically possible for larger chunks to stay together (The Armageddon movie wouldn't have worked, for instance, gravity would have held the two pieces together at least enough to strike earth) However, it's far more likely that smaller pieces would be drug into a different orbit by gravity, or even ejected from orbit by the larger chunks.

Assuming the pieces somehow stayed close, those pieces would likely interact rather violently, sending hunks in all directions when they eventually collided or tossing out their smaller counterparts.  Earth would most likely be struck by a civilization ending piece from this fairly quickly. The large pieces are at least just as likely to fuse back together during these impacts as they are playing bumper cars (I haven't studied impacts at all, so just really basic knowledge of this bit, but we have plenty of evidence of collision fusing out there, it might actually be more likely), but the debris would be massive. 

If any of the pieces drifted inside the Roche limit, it would be ground up by tidal forces, eventually forming equatorial rings and likely pelting the earth.   

Lord knows what the loss/changes of lunar gravity would do to the systems here on earth.
Title: Re: Astronomy/cosmology questions...
Post by: E_T on March 07, 2019, 03:35:07 PM
As well as the effects of Earth Tidal Forces on the Lunar Debris.