Where does the term “blue moon” come from?
The term “blue moon” probably comes from the fact that, on very rare occassions, the moon actually appears to be blue. This usually happens after a volcanic eruption, such as Mount Pinatubo in 1991, when lots of dust is present high in the sky. Other times when the moon turned blue include the eruption of El Chichon in 1982, and Krakatao in 1883. These blue moons are so rare that the phrase “once in a blue moon” has come to mean a very rare event. The term “blue moon” was applied to the second full moon in a month due to an error in Sky and Telescope magazine in 1946. Read the gory details from Sky Publishing here.
