This October boasts a modestly rare event — two full moons in a single month, also known as a Blue Moon.
And this time it happens on Halloween, which has no scientific significance other than ohhh, spooky.
Blue Moons take place roughly every 30 months, the last one visible in the UK was back in March 2018, which was also notable for having two blue moons in the same year.
The definition of a Blue Moon can be either the second of two full moons within a single month, or a fourth full moon within the three monthly seasons – winter, spring, summer, autumn.
The idea of a Blue Moon as the second full moon in a month is quite a new one, dating to March 1946, when Sky and Telescope magazine, which contained an article called Once in a Blue Moon by James Hugh Pruett.
He accidentally simplified an old definition based on the seasonal Blue Moon, and in doing so created the modern twice monthly — and rather easier to understand idea of a Blue Moon, but even then it wasn’t until a radio show picked up on the same definition in January 1980 that it gained widespread awareness.
Incidentally, Blue Moons are not blue — unless there’s something very odd in the sky to filter the light — they are just normal full moons occurring close to each other.
This October is slightly more special as it starts with the Harvest Moon — the full moon closest to the Autumnal Equinox, which usually occurs in September, and that is always followed by October’s Harvest Moon, and having both in the same month is unusual.
And it happens on Halloween, and as it’s a Blue Moon, you really should watch An American Werewolf in London on the night.