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« Return to Thread: Part2, Joining list. Calendar reforms.
Re: Part2, Joining list. Calendar reforms.
by Irv Bromberg
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On 2009 May 20, at 16:58 , MIKE OSSIPOFF wrote:
2) The Babylonians did something interesting: They'd made very precise measurements of the Sun's movement along the ecliptic, and they knew that it moved faster during the winter than during the summer. They had a calendar that took this into account. They had a 12 month calendar, which started on an equinox, and in which each month represented the Sun's time in a particular sign of the zodiac, a particular 30 degrees along the ecliptic. I'd borrow that idea from them. The lengths of the seasons would be equal to the number of days that the sun spends in the corresponding quarters of the ecliptic. From when I checked, for instance, it seems to me that Winter would be 89 days long, and Summer would be 94 days long. If the calendar is non-fixed, then the _divisions_ of the seasons, too, would represent equal distances along the ecliptic, and their length, again, would be equal to the time that the sun spends in each division of the ecliptic.
That proposal is similar to the modern Persian astronomical calendar, which starts the year at the northward equinox with 6 x 31-day months, then the rest of the months have 30 days except for the last which has 29 days in a regular year or 30 days in a leap year. It is a good idea to have the leap day (or week or month, whatever the leap unit is) at the end of the year so that its insertion doesn't affect the ordinal numbering of any prior date in the year -- that simplifies calendrical arithmetic. The Persian scheme, even though it is an astronomical calendar for the equinox, doesn't include any rule for progressively advancing which months have 31 days in parallel with the advance of perihelion, and the 6 longer months are not centered with respect to the present or recent past position of perihelion, in fact at present perihelion is nearly 3 months before the Persian New Year Day (Norouz).
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.
Another problem is that the Earth orbital eccentricity is declining and will continue to decline for tens of millennia into the future. This will gradually reduce the seasonal length differences, making it harder to justify having 6 x 31-day months in a row, at least until the orbital eccentricity goes back on the increase.
If months are constrained to contain only a whole number of weeks then that precludes any possibility of making month lengths correspond to the position of perihelion.
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