Calendrical Ponderings

We went this evening to the sixth annual Davis community iftar, which has by now grown to be the largest such interfaith community iftar in California, with well over seven hundred people there today. The keynote speaker gave an introduction to Ramadan, and one thing she noted is that the month of Ramadan shifts throughout the solar year, it cycling through the seasons on a 33-year basis, since the Islamic calendar is strictly a lunar calendar, and the lunar year is about 11 days short of the solar year.

This year the start of Ramadan coincided with Rosh Hashanah, which is not that unlikely an occurrence since both events are keyed to the new moon, Rosh Hashanah occurring on the first of the month of Tishri. But the Hebrew calendar is a lunisolar calendar—every couple of years they stick in an extra month into the calendar, presumably so the holidays don’t migrate throughout the solar year (leading to problems like the harvest festival Sukkot being celebrated in the dead of winter). So I wonder how often does the start of Ramadan coincide with Rosh Hashanah? It does next year as well. My guess is that it usually occurs twice each 33-year cycle, but sometimes only once, and rarely three times.

All these mysteries and many more can be revealed through study of this Gregorian-Julian-Islamic-Persian-Hebrew-Mayan calendar converter.