A rare Halloween blue moon has been thrilling skywatchers across the globe.
As the second full moon of the month, it is classified as a blue moon. “In recent years, people have been using the name Blue moon for the second of two full moons in a single calendar month,” NASA explains on its website. “An older definition of Blue moon is that it’s the third of four full moons in a single season.”
Skygazers, however, should not expect the Halloween blue moon to be, well … blue. “Most Blue Moons look pale gray and white, indistinguishable from any other Moon you've ever seen,” NASA explains.
The term “blue moon” evolved to denote something that is absurd, according to Space.com, citing Philip Hiscock, a folklorist at the Memorial University of Newfoundland, in a 2012 article in Sky & Telescope magazine.
In rare circumstances, however, the moon can look blue. “A truly-blue Moon usually requires a volcanic eruption,” explains NASA. “Back in 1883, for example, people saw blue moons almost every night after the Indonesian volcano Krakatoa exploded with the force of a 100-megaton nuclear bomb. Plumes of ash rose to the very top of Earth's atmosphere, and the Moon … it turned blue!”
Fox News’ Chris Ciaccia contributed to this story. Follow James Rogers on Twitter @jamesjrogers