This year, October has two full moons. October 1 gave us the Harvest Moon, the full moon closest to the autumnal equinox..

This normally occurs in September but edged into October this year. Also known as the Full Corn Moon or Barley Moon in some parts of America, farmers have traditionally made the most of its light to gather in crops well into the night before winter sets in.

The second full moon–in 2020 of course–happens on Halloween. It’s the first Samhain full moon since 1944 when World War II was still ravaging the planet.

The second full moon in any given month is known as the Blue Moon; there are seven every 19 years. The name is something of a placeholder, given in order to keep the year’s other full moons in their rightful place. This is because the moon completes 12 full cycles of its phase in 354 days, eleven short of the full solar calendar year of 365 days.This year’s is particularly unusual as it is the first full moon to occur across all time zones since 1944, although there is a full moon on Halloween somewhere in the world every 19 years – meaning that the next one to occur will be in 2039, followed by 2058 and 2077.