A blue moon is not actually a blue moon. The moon doesn’t turn blue — even though that would pretty neat for a blue moon — but there are two different definitions for the term “blue moon”. The older definition says that a blue moon refers to the third full moon in a season with four full moons. It has something to do with correcting the lunar cycle and making sure that when people were planting and growing their crops by the moon calendar, that seasons didn’t “come too early”.
What is a Blue Moon? || My Blue Moon Correspondences
