Although the term Blue Moon refers to the second of two full moons in the same calendar month, that meaning emerged from a magazine misprint in the 1940s.

Formerly used to define the atypical fourth full moon in a quarter of the year, the term was defined incorrectly in Sky & Telescope magazine in 1946.

The game "Trivial Pursuit" reinforced the incorrect definition when it used the Sky & Telescope definition as a source for one of the game questions.

Although Sky & Telescope discovered its mistake 60 years later, a printed correction and retraction did little to reverse the incorrect definition, which was then established as common use.