For the first time since WWII, a Halloween Blue Moon will be visible across the planet to observers in the Americas, Europe, Asia, and Western Australia.
Set to occur on October 31, the event is not called "blue" due to the color of the moon, but comes from the phrase "Once in a Blue Moon" – referring in this case to the rarity of having two full moons in a single month. The first full moon of the month – called a "harvest" moon – will take place October 1.
Blue Moons occur seven times on varying dates across a 19-year cycle. The next time a Blue Moon occurs on Halloween will be in 2039. The last time such a Blue Moon was visible around the world at the same time was in 1944.
According to The Farmer's Almanac, the following full moon in November is called a Beaver Moon, as it traditionally was the best time of year to capture sheltered animals like beavers for their thick, warm pelts.