Blue moon to rise tonight

"Once in a blue moon."

The phrase has long been shorthand for something so ridiculous to imagine that it could never be real. Tonight, though, the world will see actually see one.

NASA says that a "blue moon," which is now commonly (but inaccurately) understood to mean a second full moon during a single calendar month, is expected for New Year's Eve.

The moon's revolution around the planet is on a 29.5 day cycle. Occasionally, then, Earth experiences a second full moon within one calendar month.

Tonight's spectacle is in not unusual. Scientists say it happens about every two and one-half years.

However, a blue moon on December 31 is rare. It last happened in 1990.

The first known use of the phrase "blue moon" occurred in the sixteenth century. It was used to argue that an event was so improbable it could never happen. Later, the phrase evolved to mean "never." 

Sometimes, though, the moon actually does appear to take on a bluish color. This last happened after a forest fire event in Canada in 1950. It also occurred following the eruption of the Krakatoa volcano in 1883. The effect is the result of an accumulation of smoke or dust particles in the atmosphere, which scatter light waves of a longer wavelength and thus make shorter waves, including those that appear blue to the human eye, more visible.

The next month in which a blue moon is expected to grace the sky is August 2012.

By the way, another common use of the phrase "blue moon" is in songs about sadness and loneliness. In the Rogers and Hart song of the same name, made popular by Elvis Presley, the lyrics speak of "standing alone without a dream in [your] heart [or] a love of your own."

Here's hoping that does not describe your New Year's Eve.