Once in a blue moon, as the saying goes, there are two full moons in a single calendar month, which NASA says actually happens every 2.5 years. A blue moon on New Year's Eve is much rarer, last happening in 1990. Even rarer, though, is the lunar eclipse that will accompany the blue moon.

Not only is the decade going to end on a blue moon -- the second appearance of a full moon in a calendar month -- but also a partial eclipse of the moon, at least for sky watchers in Europe, Africa and Asia. A partial lunar eclipse occurs when the moon is partially darkened by the Earth's shadow.