Once in a blue moon we do a post about the blue moon.
August 31st will be the second full moon this month, or what’s now commonly referred to as a blue moon. I’d assumed this was based on ancient folklore, but it’s actually a fairly recent definition.
Sky & Telescope says that calendar-based definition is a mistake, but ironically it’s a mistake that likely arose with a Sky & Telescope article in 1946, and which was later popularized on the radio.
Other definitions of “blue moon” refer to a rare occurrence, an actual description of the moon (due to volcanic particles or other odd phenomena that may make the moon appear to be blue), or the third of four full moons in a season.