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Jupiter Time |
From: "Shaun Moss" <shaun@earthmultimedia.com>
To: <time-sig@chapters.marssociety.org>
Cc: <marstime@yahoogroups.com>
Subject: RE: [Mars_Time-sig] Jupiter Calendar
Date: Fri, 19 Jul 2002 08:00:10 +1000
[ to Mars Society Time list, from "Shaun Moss" <shaun@earthmultimedia.com> ]
Hi
I have written a Jovian calendar, although I haven't put it on the Mars Engineering website yet. It is much simpler than Tom Gangale's. Only two astronomical cycles are used as it's basis. The Ganymedean solar day is used as a Jovian "week", as is almost the exact same length as an Earth or Mars week. A Jovian "day" (I call them J-days) is simply equal to one-seventh of the J-week, which makes the J-day (24 hrs 34 mins) almost the exact same length as a sol, and only slightly longer than an day.
I do not attempt to exploit the harmonic resonance of Io, Europa, and Ganymede in the calendar, even though this information will prove useful to the colonists (especially the inter-moon bus companies). If the harmonic resonance was exact then I would, but it isn't, which results in 4 separate, if similar, calendars. There will be activity throughout the Jovian system and it will be much easier for them if they all use the same calendar.
The other reason I use to justify this choice is that I expect that 90% of Jovians will settle on Ganymede and Callisto. The non-Galilean moons are too small to serve in any capacity other than space stations. Io and Europa are very dangerous paces to live. Io is highly volcanic and it would be hard to colonize on a large scale, although I'm sure there would be safe places to build bases. Europa appears to regularly have large floods, and it would be difficult to find rock and metals there with which to build. These could be imported, of course.
On the other hand, Ganymede and Callisto are solid and not geologically active (although Ganymede was once). They are rocky as well as icy, so there are plenty of resources for colonists. Also these are the two largest moons, which means plenty of surface area, and the highest gravity levels. Humans will probably prefer the higher gravity because of less bone damage, and less recovery time if travelling/returning to Mars or Earth.
Callisto and Ganymede do not have as neat a harmonic resonance as I, E, and G. The relationship is about 8 Callistan days equals 19 Ganymedean. This is too tricky to incorporate into the calendar, so in the interests of creating a simpler calendar which can be used throughout the whole Jovian system, I am using a J-day based only on the Ganymede solar day.
For years, I refer to the "big year" and the "small year". A big year equals one orbital period of Jupiter, about 11.86 Earth years. A small year is one twelfth of that, a period only 4 days shorter than an Earth year. A month is one twelfth of a small year, which comes to almost exactly 30 days. A big year therefore has 144 months.
Shaun Moss
www.earthmultimedia.com
www.marsengineering.com
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