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Rosh Chodesh

Alvin Stern

Recently I was asked a question about the occurrence of one day of Rosh Chodesh or two days of Rosh Chodesh.  So, in this month’s article, I will explain when we have these situations.   First, recall that the solar calendar is based on a year of 365 ¼ days – which requires a correction every four years of a Leap Day.  The lunar calendar is based on a year of 354 days.  If one observes simply a lunar calendar, as the Moslems do, then annual observances shift each year relative to the solar cycle.  Judaism is based on a mixture of these two cycles – our months are lunar based, as is our year, but we make periodic corrections to allow our annual holidays to remain fixed in their season – since Pesach is known as Chag HaAviv – the Holiday of Springtime, it must fall in the spring and therefore our calendar introduces a leap month every few years to keep Pesach in late March or April.  This Leap Year occurs 7 times in a 19 year cycle, so that after a complete 19 years the Hebrew date and the English date once again coincide – this past spring Yom HaAtzmaut (5 Iyar) fell on May 14, the same date as in 1948, which makes sense since this was the 57th Anniversary of the State of Israel’s founding and 57 is the end of the third 19 year cycle.

Within each year, there are certain holidays which cannot fall on certain days of the week – for example, Yom Kippur doesn’t fall on Friday or Sunday, to avoid desecrating the Shabbat by preparing for breaking of the fast or beginning the fast; Rosh Hashana doesn’t start on Sunday, since that would put Hoshana Rabbah on Shabbat which would cause a problem with using the Lulav and Etrog on that day, and the beating of the Hoshanot (the willow branches we beat to symbolically rid ourselves of sin).   So we need a mechanism for making some shifts in the days of the week as the year progresses.

Now, we can finally talk about Rosh Chodesh being one or two days!  Our Hebrew months are either 29 or 30 days in length; all but 2 months are always either 29 or 30 days.  Kislev, for example (the month in which Hanukah starts) is one that can vary – so some years the holiday ends on the 2nd of Tevet and other years on the 3rd of that month.  Tishrei, on the other hand, is always 30 days, and Adar (in non leap years) and Adar Bet (the added month in a leap year) are always 29 days long.  By adding the extra days to the two flexible months, the calendar is able to shift as needed.

Rosh Chodesh is the Head of the New Month – when the previous month had only 29 days, the first day of the new month is a single day of Rosh Chodesh, but when the previous month had 30 days, the last day of the month concluding is celebrated as the first day of Rosh Chodesh and the first day of the new month is the second day of Rosh Chodesh.  So, when Av ended with its 30 days, Rosh Chodesh Ellul was celebrated for two days, and the second day is the day when we began blowing the shofar to announce the coming of Rosh HaShana.  Since the first day of Rosh Chodesh was still Av, we didn’t sound the shofar then. 

Whether Rosh Chodesh is celebrated for one or two days, it is a holiday to remind us of the cycle of nature, and to remind ourselves that we frequently have an opportunity to start afresh.  We recite Hallel in thanksgiving for this chance to renew ourselves each month.