Jewish Astronomy: The Moon

Did you know that you can tell where you are in the Jewish month, just by looking at the night sky?

Every Jewish month begins on the New Moon, when the sky is darkest. We call that day Rosh Chodesh, “Head of the Month.”  In ancient times, that’s how the calendar was set: experienced Jews would look at the sky from the Temple Mount and decide when it was the New Moon. They would then make the official announcement of the arrival of the new month.

So if the moon is dark, it’s a new Jewish month. To find out which month, consult a Jewish calendar.  <- If you click on that link, it will take you to the niftiest Jewish calendar imaginable. If I could access only one website, it would be hebcal.com, no kidding.

If the moon is waxing (appearing to grow larger) then we are in the first half of the month. If it is waning (appearing to grow smaller) a new month is coming. Some Jewish holidays (Purim and Passover, for example) begin near the 15th of the month: no surprise there, it’s the Full Moon!

This is also the reason that the Jewish calendar sometimes seems crazy relative to the secular calendar. The Jewish year is lunar (matched to the moon) with periodic adjustments to keep it in sync with the seasons (the solar year.) So some years the holidays seem “early” or sometimes “late.” Really, they’re right on time.

The best thing to do is to get a Jewish calendar and use it. But some things you can know just by looking at the sky: “It’s Rosh Chodesh!” you can say, whenever you see the New Moon.

“Why bother with a separate calendar?” some might ask. The beauty of the Jewish Calendar is that it brings us into sync with the rhythms of nature.  Days begin at sundown, not at a mark on a clock. Months begin when the moon is dark; they swell and then fade.  While we can learn details and names from a calendar or a website, the plain facts of Jewish time are in the sky above us, if we are only willing to go outside and look.