What is a Blue Moon?
A rare Blue Moon captivated many late Tuesday and early Wednesday as the inspiration for several romantic songs passed over the night sky.
A Blue Moon is an extra full moon that appears in a subdivision of a year, either the third of four full moons in a season or a second full moon in a month of the common calendar. This year, it was the second full moon in a month.
Metaphorically, a “Blue Moon” is a rare event, as in the expression “Once in a Blue Moon.” However, the phrase has nothing to do with the actual color of the moon, although a literal “Blue Moon” (the moon appearing with a tinge of blue) can occur in certain atmospheric conditions (volcanic eruptions or large fires).
According to the Farmer’s Alamanac, “the suggestion has been made that the term “Blue Moon” for “intercalary month” arose by folk etymology, the “blue” replacing the no-longer-understood belewe, ‘to betray’. The original meaning would then have been “betrayer moon”, referring to a full moon which would “normally” (in non-intercalating years) be the full moon of spring, while in intercalating year, it was “traitorous” in the sense that people would have had to continue fasting for another month in accordance with the season of Lent.”