You might not be able to celebrate Halloween in a traditional fashion this year. Trick-or-treating may not be possible, massive Halloween blowouts will almost certainly be canceled or scaled down dramatically, and haunted houses will require zombies to maintain a six-foot distance while scaring patrons. Whatever happens this October, at least one thing is for sure: There will be a blue moon on Halloween night.
A blue moon is a rare phenomenon referring to the second full moon in one month. Since a full moon occurs once every 29 days, usually there’s only one per month. In October, the first full moon falls on October 1, while the second will be October 31.
According to NASA, blue moons only occur once every two-and-a-half to three years, which really makes you appreciate the phrase “once in a blue moon.” Given the rarity of a typical blue moon, it’s even more special and unlikely that this blue moon falls exactly on Halloween night. That particular celestial event occurs only three or four times per century (the next won’t happen until Halloween 2039).
Unfortunately a blue moon doesn’t actually appear blue in the sky, although that would certainly be in keeping with the spirit of Halloween.