where did the blue moon get its name
Blue moon The term has traditionally referred to an "extra" moon, where a year which normally has 12 moons has 13 instead. The "blue moon" reference is applied to the third moon in a season with four moons,[2] thus correcting the timing of the last month of a season that would have otherwise been expected too early. This happens every two to three years (seven times in the Metonic cycle of 19 years).[3] The March 1946 issue of Sky & Telescope misinterpreted the traditional definition, which led to the modern colloquial misunderstanding that a blue moon is a second full moon in a single solar calendar month with no seasonal link.