Friday, March 19, 2010

[stizembd] Lunar holidays

Suppose, for variety, you wished to celebrate various holidays at different times of the year: Christmas in summer, for example.   In this modern age, there is no actual need that certain holidays must fall in a certain season (e.g., harvest). How would one systematically change holiday dates?

One way is to keep the holiday dates the same, but change the length of the year so that it is not exactly the solar year. Over the years, the calendar year and the astronomical solar year become offset, allowing the holidays to drift through the seasons. One commonly used calendar already does this: the Islamic calendar, which has 12 lunar months in a year.  Instead of attempting to reinvent the wheel, let's just use the Islamic calendar, possibly renaming the month names to our names, and marking holidays as fixed (or "fixed" as in "fourth Thursday of the 11 month") on that calendar. The Fourth of July is celebrated on the 4th day of the 7th month, which will not remain fixed in the middle of summer. Christmas is celebrated (or is started celebrated) on the 25th day of the 12th month. Some years, it may end up in the middle of the summer.

The holidays varying within the seasonal year allows variation on how to celebrate it. Celebrate Christmas in the middle of summer, at the beach? (The Australians probably already do this, though the Australians conversely have never experienced a winter white Christmas.)

One problematic holiday is Halloween: no month in the Islamic calendar has 31 days. Instead, let's make Halloween, or All Hallows' Eve, the day before All Hallows' Day, which is November 1.  The observational calendar as is Islamic practice would not work so well for this, as you would not know in advance when the next month begins, so a tabulated calendar is recommended.

It's blasphemous in probably two if not three religions, but we can systemically define Easter as the first Sunday after Passover, and define Passover as the 15th day of the 4th month. Because the Islamic calendar is not tied to the seasons, Passover, as well as Easter, will wander around the solar year. Or, alternatively, if the seasonal aspect of a particular holiday is deemed important, one can still define holidays as, for example Easter, "the Sunday after the first Friday after the first full moon after the vernal equinox" if you wish.

One slightly interesting effect is, because it is a lunar calendar, the holidays will always coincide with a phase of the moon, which is not the case with the solar Gregorian calendar. Under a lunar calendar, which begins each month with at a new moon, we will never experience a full moon on Halloween (like this past October) or New Years. Lunar eclipses can only occur on (about) the 15th on the month, and solar eclipses can only occur on (about) the first.

Inspired by "It wish it were warmer for Halloween."

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