An airplane is silhouetted against the bright full Moon.
Source: NASA/Joel Kowsky
Published: May 16, 2019
Historical Date: July 31, 2015

A plane is seen flying in front of the second full moon for the month of July, Friday, July 31, 2015 in Arlington, Va.

In recent years, people have been using the name Blue Moon for the second of two full moons in a single calendar month. An older definition of Blue Moon is that it’s the third of four full moons in a single season.

ENLARGE

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