There will be a Blue Moon this New Year’s Eve! The Moon will be so large and bright that it’s supposed to be visible in New York’s Times Square! 
For more than half a century, whenever two full moons appeared in a single month (which happens every 2 1/2 to 3 years), the second has been called a “Blue Moon.” In our lexicon, we describe an unusual event as happening “once in a blue moon.” This expression was first noted back in 1821 and refers to occurrences that are uncommon.
After large forest fires or major volcanic eruptions the Moon has reportedly taken on a bluish or lavender hue. Soot and ash particles, propelled high into Earth’s atmosphere, can sometimes make the Moon appear bluish.
Another definition, which was recorded in the early issues of Maine Farmer’s Almanac, describes a “Blue Moon” as the third full moon in a season that has four full moons.
Over the next 20 years there will be about 15 blue moons, with an almost equal number of both types of blue moon occuring. No blue moon of any kind will occur in 2011, 2014 and 2017.
One explanation connects it with the word “belewe” from the Old English, meaning “to betray.” It can also mean “blue” or “to fool”–perhaps because it betrayed the usual perception of one full moon a month.
“Blue moon” appears to have been a colloquial expression in England long before it appeared in an American almanac! According to the Oxford English Dictionary, the first reference to a blue moon comes from a ditty recorded in 1528: “If they say the moon is blue, We must believe that it is true.”
For a fuller explanation of a Blue Moon see the article on InconstantMoon.com here.
For more background information on the controversy over the two definitions of Blue Moon, see the Sky and Telescope article, “What’s a Blue Moon?” here.
As we end this year and move on to another one, Leah and I both offer our warmest wishes to all for a very happy, healthy, and good New Year!
To our reviewers and guest bloggers – Thank you for volunteering your time and expertise. It has been invaluable to Quo Vadis, and also to your peers in various communities and social networks. We are very appreciative of all the insightful and constructive comments and suggestions we have received via this blog or email; and for great photos for our flickr album and blog banner. And thank you, too, for the expressions of encouragement and support. They have meant a lot to us. Leah and I have remarked this blog often has the feeling we are all talking together as a group of friends.
Again, our deepest thanks, and best wishes for 2010.
