Once in a Blue Moon

A blue moon will grace the night sky Friday night, giving skywatchers their last chance to observe this celestial phenomenon for nearly three years. 

The moon will wax to its full phase at 9:58 a.m. EDT Friday, bringing August's full moon count to two (the first one occurred Aug. 1). Two full moons won't rise in a single month again until July 2015.

But don't expect tonight's full moon to actually appear blue, unless you're peering through a thick haze of volcanic ash or forest fire smoke. "Blue moon" is not a reference to the satellite's observed color.

The term has long been used to describe rare or absurd happenings. And farmers once employed it to denote the third full moon in a season — spring, summer, autumn or winter — that has four full moons instead of the usual three.

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