By David L. Brown
When something unusual happens, we often hear that it was “once in a Blue Moon.” But how rare to experience a “blue moon” on a very special day, New Year’s Eve. Tomorrow you can witness that even more unusual event.
The term has nothing to do with the color of the moon — it will look just the same as any other full moon. I took the picture below in Navajo Country in northwestern New Mexico as a full moon rose over the desert.
We call it a blue moon when a second full moon appears during a single month. This month the Moon was full on December 2, and will be again on December 31, so that identifies the New Years Eve moon as a blue one.
Why are the appearances of blue moons unusual events? Most years have twelve full moons, taking place about once every month (the words “month” and “moon” come from the same Old English root). But the period of the moon’s orbit around the Earth isn’t quite a month long, so at the end of every year there are a few extra days. Those days add up and about every 2.7 years there is an extra full moon to make up the difference.
There are many theories where the term came from. One relates to the fact that in Medieval times the English clergy used the phases of the moon to determine the dates for Lent and Easter. If a full moon appeared too early, it was called a “betrayer moon,” using the Old English word “belewe,” meaning either betrayer or blue. Later English writers confused the two meanings.
Whatever the reasons, what better way to celebrate the end of the year just ending than to step outside and observe the rising full moon. For once in how many blue moons will it be before such events will occur together? Because of geometry, a full moon always rises in the East opposite the setting sun, so right after dark is a good time to view Luna in her splendor.
But if you wait until the traditional Midnight, the moment of the changing of the year, it may be an even more spectacular sight, for then the blue moon will be shining brightly from directly overhead, halfway across the sky.
Happy New Year.