Saturday, June 23, 2007

Will We Have a Blue Moon This June?

After checking the star chart for June at, I saw that we're expecting a second full moon this month on the 29th! How exciting; a blue moon. With the moon cycle being 28 days and a month being 30 and 31 days (usually--no need to be so picky!), a second full moon can't be that uncommon and would belie the well-worn phrase 'once in a blue moon.' So wouldn't you know that all it required was a search (isn't the internet a great way to find out almost useless info) and the people at Sky and Telescope have the answer!
Instead of the calendar year running from January 1st through December 31st, the almanac relies on the tropical year, defined as extending from one winter solstice ("Yule") to the next. Most tropical years contain 12 full Moons — three each in winter, spring, summer, and fall — and each is named for an activity appropriate to the time of year (such as the Harvest Moon in autumn). But occasionally a tropical year contains 13 full Moons, such that one season has four rather than the usual three.

It is actually a bit more complicated than this, but it does indicate an appropriately rare occurrence.

No comments: