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Astronomical sidereal calendar (was: Part2, Joining list. Calendar reforms)

by Amos Shapir :: Rate this Message:

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A tropical calendar may be difficult, but this can be made simpler by defining the calendar along the sidereal year. A convenient cycle is 366 years with 95 leap (year Y is leap if (Y mod 27) mod 4 == 3); it can be started on apphelion or perihelion day, with 5 or 6 long months around the apphelion, the same way the Iranian calendar does.

To make it into a tropical calendar, just shift the starting day by 1 day every 57 years (that may change in the future), but keep month lengths the same as the overlapping sidereal months.

A lunar calendar of 122 years, 1509 months, can be superimposed on the same cycle. Longer lunar months should be concentrated around the perihelion, by keeping leap months and days closer to that point.

(Perl source is available if anyone wants the gory details)

Amos Shapir

Date: Sat, 23 May 2009 23:34:25 -0400
From: irv.bromberg@...
Subject: Re: Part2, Joining list. Calendar reforms.
To: CALNDR-L@...

...

If you look in the archives of this CALNDR LISTSERV you will see some threads about Shriramana Sharma's STAY calendar, which was proposed as an astronomical calendar that would have a rule for advancing which 6 months would have 31 days. The proposal proved problematic to actually implement in calendar arithmetic, Shriramana never got it working. I also tried and gave up. It is difficult to avoid oscillations of the 31-day months from year-to-year unless special rules are adopted to prevent such oscillations. Such rules could include using the mean perihelion instead of the actual perihelion, and probably not changing the month lengths more frequently than at century boundaries.

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