Op-Ed: Jewish and Chinese Calendars
The Gregorian calendar—the most commonly used calendar on earth today--is solar. It is based on the time it takes the earth to go around the sun, which is a tiny bit less than 365 ¼ days. The months are arbitrary. They are called “months” because they are a reflection of the lunar cycle—the time it takes for the moon to circle the earth.. A lunar month is 29 days, 12 hours, 44 minutes and 3 seconds long. On lunar calendars, months typically are either 29 or 30 days long.
The Islamic calendar is lunar. Since 12 lunar months don’t add up to 365 ¼ days, the Islamic months occur a bit earlier every solar year. The month of Ramadan will begin on June 29 in 2014. Since Muslims are required to fast during the day and eat only at night, the fast will be extremely long at northern latitudes. Twenty years ago, in 1994, Ramadan began on February 12. When a calendar is lunar, the holidays move around the year, and so the fast in the northern hemisphere was noticeably shorter in 1994 than it will be in 2014.
The Jewish and Chinese calendars are solar-lunar. A month is a real month—the time it takes for the moon to circle the earth. A year is a real year—the time it takes for the earth to circle the sun. Since the lunar months don’t quite add up to a year, an extra month is added in leap years. In both calendars, leap years occur 7 times every 19 years.
Sometimes, a Chinese year begins on the first day of Shvat, the month before Adar, rather than the first day of Adar. That’s because Chinese and Jewish leap years don’t always coincide. Even though both calendars add a month 7 times every 19 years, the leap years don’t have to take place the same year. 7 and 19 are both prime numbers, and 19 divided by 7 is between 2 and 3, and so the time between leap years is either two or three years.
The current Jewish year, 5774, is a leap year. There will be two months of Adar this year. Whenever there are two Adars, the Chinese year begins on the day when Adar I will begin at sundown. Adar I will begin at sundown on January 31, the day that the Chinese Year of the Horse arrives at 12:01 A.M.
Jewish and Chinese holidays often occur on the full moon. The Jewish holiday Sukkot often coincides with Chinese Mid-Autumn Festival, also known as Moon Cake day. In 2014, these two holidays will be a month apart, since both the Chinese and Jewish years are leap years, but the extra month on the Chinese calendar is added at the very end of the year, generally in late January.
Sometimes the Jewish holiday of Purim coincides with Chinese Lantern Festival. Both are cheerful days occurring on a full moon. Since there are two Adars in 5774, and since Purim occurs in Adar II when that happens, they will be a month apart this year.
Hanukkah is an exception to the common occurrence of Jewish holidays at the time of the full moon. It begins on the 25th of Kislev, when there are two remaining days of the waning moon. Then come four days with no moon at all, followed by the first two days of the waxing moon. Hanukkah is on the darkest nights of the year (at least, in the northern hemisphere) when the days are shortest and there is either no moon or merely the last two or the first two of the lunar cycle. It is a perfect time for the Festival of Lights. (Christmas was set on the 25th of December, an echo of the 25th of Kislev. It too occurs at a dark time of the year and is associated with lights, but since the Gregorian calendar is solar and not solar-lunar, it is possible for a full moon to take place at Christmas.)
A solar-lunar calendar and holidays on the full moon are two of the similarities between Chinese and Jewish traditions. There are cultural similarities as well: Jewish and Chinese children are likely to do well in school. On the other hand, there is nothing in Chinese tradition that in any way resembles Kashrut, since pork, dog meat, and donkey meat are all part of China’s culinary traditions.