Friday, August 3, 2012

If Judaism and Islam Both Use Lunar Calendars, Why Are They So Different?

amazon reviewed Jewish Calendars

Dear Tanta Golda,
There’s been talk in the news about the Islamic holiday of Ramadan and how their lunar calendar works. It got me thinking, I know that the Jewish calendar is also lunar and has something to do with why the holidays seem to change every year, but I don’t really get it. Rosh Hashannah is always in September, but I remember when Ramadan was in October and now it’s in July.
Lunar Lunatic
Dear Loony,
The short answer: Yes, they’re both lunar, but both are modified lunar calendars.
For reference, most of the world follows the Gregorian calendar, introduced in 1582 by Pope Gregory XIII, based on our rotation around the sun. One complete circuit=one complete year.
Many traditional societies follow(ed) a lunar calendar: one based on the cycle of the waxing and waning of the moon. In a true lunar calendar, each lunar month begins at the time of the monthly "conjunction", when the Moon is located on a straight line between the Earth and the Sun. Months alternate between 29-30 days. With one day added every 3 years. Both Judaism and Islam use some form of lunar calendar.
Islam’s calendar is close to a ‘pure’ lunar calendar. It consists of 12 lunar months in a year of 354 or 355 days. Being a lunar calendar, it is not synchronized with the seasons. With an annual drift of 10 or 11 days, the seasonal relation repeats about every 33 Islamic years. This is why Ramadan began in July this year. Each month begins when a crescent moon - or ‘new moon’ is sighted at sundown after the 29th day. If for some reason it is not sighted (clouds, the sky is too bright when the moon sets) then the month continues through the 30th day. (This lead this year to different countries beginning Ramadan on different days.) Years in the Islamic tradition are counted from the time Mohammed travelled to Medina. This is the year 1433.
Judaism follows many of the same practices, with modifications. However, in practice we follow a lunisolar calendar: a combination of lunar and solar cycles. It takes about 12 ½ lunar cycles for the Earth to travel around the sun. If we only followed the lunar cycles we would soon be celebrating Hannukah during the summer. To correct for this the Jewish calendar adds a leap month every 2-3 years. It comes after the month of Adar, and is called, creatively, Adar II. This means that Passover always occurs in the spring, Hannukah in the dark days of winter, and the High Holy Days - my little moonbeam - can start as early as September 4th (2013) or as late as September 28th (2011), but never in July or December. Years in the Jewish tradition are counted from the creation of the world. (Feel free to ask that lovely young man Rabbi Jeremy how the ancient rabbis determined this.) This year we enter the year 5773.
I hope this answers your question. Please keep sending your queries to

amazon reviewed Jewish Calendars