Is the Moon Really Blue?


July marks the only Blue Moon until 2018, but it’s not really blue, is it?

Blue Moon is a misnomer that often causes confusion.   It has nothing to do with the color of the Moon, although certain atmospheric conditions can give the moon a blue tint.   Historically, a Blue Moon was defined in the Maine Farmer’s Almanac as the third full moon of a season containing four, instead of its normal three.   The naming of this extra moon was in keeping with tradition of Full Moon names.

Full Moon Names

More recently, Blue Moon has become the second full moon of a calendar month.   This definition was based on a March 1946 Sky and Telescope article by James Pruett, called “Once in a Blue Moon”.    Mr. Pruett had distilled the Maine Farmer’s Almanac information to mean the second full moon of a month being the Blue Moon.   This didn’t begin to gain popularity until the reference resurfaced in a 1980 broadcast of the popular astronomy radio program, “Star Date”.   It was later reinforced by the addition of this fact in the Trivial Pursuit board game.

The “Once in a Blue Moon” title of Pruett’s article is supposed to mean rare or infrequent. Ironically, it is the Maine Farmer’s Almanac meaning of Blue Moon that has the distinction of being more rare.    Two full moons in a calendar month occurs nearly 40% more frequently.  However, after this month you will not see another calendar-month Blue Moon until 2018 but you’ll be rewarded with two of them, one in January and the other March.

Don’t forget to keep looking at the Moon and other astronomical beauties and check back with us often as we help you……Explore Where You Are™


About Author

Chris Morrison

Chris is an avid amateur astronomer, birder, photographer and general nature and science nut. He was a Vice President at a major telescope manufacturer, where he was directly involved in product development and testing for much of his 15 year tenure. His passion for all things science and nature is what led him to found, an online outlet for his desire to share his love of the natural world.

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