Alpha Centauri 2

Sid Meier's Alpha Centauri & Alien Crossfire => The Theory of Everything => Topic started by: Yitzi on December 31, 2014, 04:10:38 AM

Title: A thought about Planet's calendar
Post by: Yitzi on December 31, 2014, 04:10:38 AM
I was looking over the information about Planet (appendix 5 in the manual), and it occurred to me:

While the colonists would probably continue to use Earth years in an official capacity, it is fairly likely, at least among more Planet-focused factions such as the Gaians, that Planetary years would be used in an unofficial capacity.  Well, not quite.

You see, Planet doesn't have seasons the way Earth does, due to its near-zero axial tilt.  As a result, its 532-day-long (in Planet's shorter days) orbital period is not really significant.

Well, it's not significant in terms of Planet's position around Alpha Centauri A.  However, Alpha Centauri B (Hercules) is a very notable star (easily bright enough to read by at night), and so the period of year in which it is visible at night would be markedly different than the period of year in which it is visible during the day.  As such, this is probably the most likely way to calculate a Planetary "year".

However, this "year" is not exactly those 532 days, because Hercules also moves in relation to Alpha Centauri A. If we assume that Planet and Hercules orbit Alpha Centauri A in the same direction, the year comes out to roughly 540 days.  As such, there would likely be 12 months (carrying over the names from Earth) of 45 days each (with December sometimes being 44, or maybe 46 depending on how the rounding works out), with the new year defined as the day on which Hercules passes the center of the sun (it takes most of a day to pass the sun, so there's a good chance that it won't do it all in the same day).
Title: Re: A thought about Planet's calendar
Post by: Lord Avalon on December 31, 2014, 08:44:45 AM
Thoughts on Planet day units:

A Planet day is 17.53 earth hours. dy(p) = 17.53 hr(e) * 3600 s/hr(e) = 63,108 s. Not a very nice round number.

Let's round to 63.1 ks. If you go kinda metric and divide the day into 20 parts, a Planet hour: hr(p) = 3155 s.

If you kept Planet hour close to hr(e) and divided dy(p) into 18 hr(p'), then 63,108 / 18 = hr(p') = 3506 s.

So earth minutes don't fit very well. I suppose with the 18 hr(p')/ dy(p), you could say there are 35 hectosecs per Planet hour - 35 hs/ hr(p'), but that leaves an extra 1 hs/ dy(p) and change.
Title: Re: A thought about Planet's calendar
Post by: Yitzi on December 31, 2014, 12:07:17 PM
Thoughts on Planet day units:

A Planet day is 17.53 earth hours. dy(p) = 17.53 hr(e) * 3600 s/hr(e) = 63,108 s. Not a very nice round number.

Let's round to 63.1 ks. If you go kinda metric and divide the day into 20 parts, a Planet hour: hr(p) = 3155 s.

If you kept Planet hour close to hr(e) and divided dy(p) into 18 hr(p'), then 63,108 / 18 = hr(p') = 3506 s.

So earth minutes don't fit very well. I suppose with the 18 hr(p')/ dy(p), you could say there are 35 hectosecs per Planet hour - 35 hs/ hr(p'), but that leaves an extra 1 hs/ dy(p) and change.

True, unless they have Planet seconds be just a tiny bit longer than Earth seconds...

But that's more flexible in any case, since the day is the only period there with physical significance.
Title: Re: A thought about Planet's calendar
Post by: gwillybj on December 31, 2014, 01:49:21 PM
Would, after a very few generations, the sleep/wake rhythms of the human body adapt to the local circumstances?
The local year (one circuit of the primary star) could then be 532 local days of 18 hours (of 60 minutes of 60 seconds, seconds being a measure that doesn't change), and "leap days" could be calculated and added or subtracted as necessary to make some kind of standard cycle, similar to how the 19-year cycle of the Hebrew calendar is done.
As for the appearance of Hercules, its cycle is already known and could be noted in almanacs and ephemirides so there would be no surprise when the time came for the "native wildlife" to become restless.
Title: Re: A thought about Planet's calendar
Post by: Yitzi on December 31, 2014, 04:10:22 PM
Would, after a very few generations, the sleep/wake rhythms of the human body adapt to the local circumstances?
The local year (one circuit of the primary star) could then be 532 local days of 18 hours (of 60 minutes of 60 seconds, seconds being a measure that doesn't change), and "leap days" could be calculated and added or subtracted as necessary to make some kind of standard cycle, similar to how the 19-year cycle of the Hebrew calendar is done.

That would make the days also be slightly off from the day-night cycle, which defeats the purpose of having them local.

And I'm arguing that there isn't really any point in defining a "year" by the circuit of the primary star, because unlike Earth there are no seasons to speak of anyway.  The primary effect of that circuit is in how it affects the relative positions of the primary star and Hercules, but that actually comes out to a cycle slightly longer than Chiron's orbital period.

Quote
As for the appearance of Hercules, its cycle is already known and could be noted in almanacs and ephemirides so there would be no surprise when the time came for the "native wildlife" to become restless.

No question that it'd be known, but the time of day when it's visible would still be a much more notable "seasonal" variation than anything that goes purely as Chiron's orbital period.
Title: Re: A thought about Planet's calendar
Post by: gwillybj on December 31, 2014, 06:18:13 PM
I think I caught on: Set the ephemerical timing on the Hercules/Chiron alignment with A (and the perihelion event), then assign some manageable number of days to a secular year and month system?

(On what are the Mission Years based? Earth years?)
Title: Re: A thought about Planet's calendar
Post by: Lord Avalon on December 31, 2014, 08:05:25 PM
Thoughts on Planet day units:

A Planet day is 17.53 earth hours. dy(p) = 17.53 hr(e) * 3600 s/hr(e) = 63,108 s. Not a very nice round number.

Let's round to 63.1 ks. If you go kinda metric and divide the day into 20 parts, a Planet hour: hr(p) = 3155 s.

If you kept Planet hour close to hr(e) and divided dy(p) into 18 hr(p'), then 63,108 / 18 = hr(p') = 3506 s.

So earth minutes don't fit very well. I suppose with the 18 hr(p')/ dy(p), you could say there are 35 hectosecs per Planet hour - 35 hs/ hr(p'), but that leaves an extra 1 hs/ dy(p) and change.

True, unless they have Planet seconds be just a tiny bit longer than Earth seconds...

But that's more flexible in any case, since the day is the only period there with physical significance.
A second is a fundamental unit, so I don't see that changing.

As far as a calendar goes, I would have 12 months be of 44 dy(p), so the four extra days could be a Landing Festival.
Title: Re: A thought about Planet's calendar
Post by: Yitzi on December 31, 2014, 08:19:30 PM
I think I caught on: Set the ephemerical timing on the Hercules/Chiron alignment with A (and the perihelion event), then assign some manageable number of days to a secular year and month system?

Not quite; perihilion is essentially irrelevant (except that it'd come out that the number of Planetary years from perihilion to perihilion is almost* exactly 1 less than the number of orbital periods from perihilion to perhilion).  It'd purely be based on the Hercules-Chiron-A angle, since that is what causes "June" to be noticeably different than "December" (especially at night).

*With the difference being purely due to the procession of Hercules.

Quote
(On what are the Mission Years based? Earth years?)

Presumably, otherwise there'd be no point in starting at 2100.
Title: Re: A thought about Planet's calendar
Post by: Buster's Uncle on December 31, 2014, 09:46:17 PM
I have to wonder - what would be the point?

A calendar is useful mostly for consensus timekeeping and agricultural planning.  The colonists brought a consensus calendar with them from Earth, and in an industrialized society on a planet without seasons where everyone lives indoors, one that conforms to local conditions has little to offer highly-mechanized and not-close-to-nature farming industry.
Title: Re: A thought about Planet's calendar
Post by: Yitzi on December 31, 2014, 10:12:56 PM
I have to wonder - what would be the point?

A calendar is useful mostly for consensus timekeeping and agricultural planning.  The colonists brought a consensus calendar with them from Earth, and in an industrialized society on a planet without seasons where everyone lives indoors, one that conforms to local conditions has little to offer highly-mechanized and not-close-to-nature farming industry.

I think that a calendar also serves the purpose of breaking time up into more manageable chunks, preferably in a manner that reflects natural cycles.  This is why you get lunar calendars, for instance, which are clearly not relevant to agricultural planning and have limited advantage over arbitrary ones for consensus timekeeping.  On Planet, Hercules is much more prominent than the moons, so it would likely use that instead, possibly with weeks based off of Nessus' cycle (although the Believers would presumably want to keep the weeks as they are, and that could be enough to keep that from changing).
Title: Re: A thought about Planet's calendar
Post by: Buster's Uncle on December 31, 2014, 10:56:51 PM
Of course we've left out a basic Earth function so far - religion.

There's a religion or two behind every single calendar system I can think of prior to the French Revolution...
Title: Re: A thought about Planet's calendar
Post by: Yitzi on December 31, 2014, 10:58:19 PM
Of course we've left out a basic Earth function so far - religion.

There's a religion or two behind every single calendar system I can think of prior to the French Revolution...

True, but clearly any religious calendar will be based off of Earth's, and so there's nothing to discuss there.  (And there's no reason there can't be a secular calendar in addition to a religious one.)
Title: Re: A thought about Planet's calendar
Post by: Buster's Uncle on December 31, 2014, 11:00:47 PM
Naturally.

-Betcha Cha has his own calendar, though.
Title: Re: A thought about Planet's calendar
Post by: Geo on January 01, 2015, 05:13:15 AM
And I'm arguing that there isn't really any point in defining a "year" by the circuit of the primary star, because unlike Earth there are no seasons to speak of anyway.  The primary effect of that circuit is in how it affects the relative positions of the primary star and Hercules, but that actually comes out to a cycle slightly longer than Chiron's orbital period.

Keep in mind that Hercules' distance to Alpha Centauri A changes quite a bit during their 80 year orbit around each other. In essence, a Chiron year based on Hercules' appearance in the sky would be longer during aphelion, and shortest during perihelion of the star.
Title: Re: A thought about Planet's calendar
Post by: Yitzi on January 01, 2015, 01:18:42 PM
Naturally.

-Betcha Cha has his own calendar, though.

Probably.

And I'm arguing that there isn't really any point in defining a "year" by the circuit of the primary star, because unlike Earth there are no seasons to speak of anyway.  The primary effect of that circuit is in how it affects the relative positions of the primary star and Hercules, but that actually comes out to a cycle slightly longer than Chiron's orbital period.

Keep in mind that Hercules' distance to Alpha Centauri A changes quite a bit during their 80 year orbit around each other. In essence, a Chiron year based on Hercules' appearance in the sky would be longer during aphelion, and shortest during perihelion of the star.

You are correct that it would change somewhat, being slightly shorter during aphelion and longer during perihelion (because Hercules moves faster during perihelion so offsets Chiron's movement by more), but only about 8 days out of the 540 are due to Hercules' movement at all (most are due to Chiron's movement around A changing the relative positions even if Hercules is treated as fixed), so it comes out to 4 or 5 extra days at perihelion and 4 missing days at aphelion.  So there would be a noticeable effect, but not a large one.
Title: Re: A thought about Planet's calendar
Post by: gwillybj on January 01, 2015, 02:33:11 PM
Lithe Days?
Title: Re: A thought about Planet's calendar
Post by: Yitzi on January 01, 2015, 03:20:40 PM
Lithe Days?

If you mean like Tolkien's, probably not; that sort of thing is usually scheduled for something that happens every year.
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