Milk ~or~ Planting

The Full Moon of May is called either the Milk or Planting Moon, and this month you'll have both! (an event that occurs only "once in a blue moon"

The next double-mooned month will be December 2009. The last occurred in July 2004. The time between one full Moon and the next, as seen from Earth, is 29 1/2 days. This is called the moon's synodic period, which is different from the true period (called sidereal) by 2 1/6Th days.

Although the actual Full Moon occurs 2 1/6th days earlier, we see it as such later because in the meantime the Earth has moved along in its own orbit. There's a 2 1/6th day drag.

The name Milk Moon is from the Anglo-Saxon word for the month; 'Thrimilce'. Did you know that cows can be milked 3 times a day in May? Since the Roman festival of the unhappy dead and that of the goddess of chastity was celebrated in May, this month has long been considered an unlucky time for marriage. This probably explains the popularity of June weddings.

Actually, a true Blue Moon occurs only when small particles in the upper atmosphere (from volcanic eruptions, forest fires, and coal burning power plants... etc) cause the Moon to appear blue. This, however, is about as rare as two Full Moons in the same month, hence the saying.

I discovered an excellent (astronomically oriented) Web Site with a Blue Moon Calculator by David Harper and Lynne Marie Stockman. It is worth a visit. Here's a snippet of output from the Obliquity WebSite

Blue Moons between 1980 and 2010