|Bright, though not full, moon in the night sky|
Neither Christianity nor Islam have a religion/holidays that have anything to do with the Land of Israel. Christianity's holiday's can be based on pagan ones which they adopted. And Islam's calendar of holidays float around the seasons, because, unlike in the Jewish Calendar, they are dissociated with the Land and seasons. There is no mechanism to periodically correct the timing of their holidays.
Jewish Holidays must fall at exactly the correct time of the solar year (agricultural season) and are celebrated on dates according to the phase of the moon. Twelve cycles of the moon are just a few days less than it takes for the earth to revolve around the sun, so without periodically adding a month the holidays and seasons will quickly be out of sync.
The Jewish calendar is based on three astronomical phenomena: the rotation of the Earth about its axis (a day); the revolution of the moon about the Earth (a month); and the revolution of the Earth about the sun (a year). These three phenomena are independent of each other, so there is no direct correlation between them. On average, the moon revolves around the Earth in about 29½ days. The Earth revolves around the sun in about 365¼ days, that is, about 12.4 lunar months.
The civil calendar used by most of the world has abandoned any correlation between the moon cycles and the month, arbitrarily setting the length of months to 28, 30 or 31 days.
The Jewish calendar, however, coordinates all three of these astronomical phenomena. Months are either 29 or 30 days, corresponding to the 29½-day lunar cycle. Years are either 12 or 13 months, corresponding to the 12.4 month solar cycle.
The lunar month on the Jewish calendar begins when the first sliver of moon becomes visible after the dark of the moon. In ancient times, the new months used to be determined by observation. When people observed the new moon, they would notify the Sanhedrin. When the Sanhedrin heard testimony from two independent, reliable eyewitnesses that the new moon occurred on a certain date, they would declare the rosh chodesh (first of the month) and send out messengers to tell people when the month began.
The problem with strictly lunar calendars is that there are approximately 12.4 lunar months in every solar year, so a 12-month lunar calendar is about 11 days shorter than a solar year and a 13-month lunar is about 19 longer than a solar year. The months drift around the seasons on such a calendar: on a 12-month lunar calendar, the month of Nissan, which is supposed to occur in the Spring, would occur 11 days earlier in the season each year, eventually occurring in the Winter, the Fall, the Summer, and then the Spring again. On a 13-month lunar calendar, the same thing would happen in the other direction, and faster. (Judaism 101)
...in an attempt to coordinate the traditional lunar year with the solar year Judaism has worked out a system of 19-year cycles, in which there are seven leap years. In distinction to the day added to the secular leap year, the Jewish calendar adds a full month to the end of its year. In this manner the Jewish holidays fluctuate by about a month or so in relationship to the Gregorian calendar, but always fall at the same time of year. (My Jewish Learning)A complex mathematical system was set up, pre-computer, to periodically compensate with an extra winter month. That's why some some years have thirteen months and others just twelve. Also the cycles of the moon sometimes take twenty-nine days and other times thirty. That creates a situation that periodically deprives people, like my youngest, of a birthday.
Unlike in Biblical times, when Rosh Chodesh was only known after the first sign of the "new moon" was spotted, nowadays we know in advance. So, I'm taking this opportunity to remind you that next week, yes, this coming Friday will be Rosh Chodesh Cheshvan.
Friday, October 20, 2017
Ladies, please join us for Rosh Chodesh Prayers! In the meantime, Shabbat Shalom.