Many people are definitely familiar with the phrase “once in a blue moon”. The notion of a “blue moon” can be said to mean “rare” or “not very often”.

A full moon cycle lasts about 29.5 days, making up a lunar month. Hence, most months only have one full moon. October 2020’s last full moon occurred on October 1st. This October 31st will be quite interesting, as it plays host to the second full moon with a month. This phenomenon is called the “blue moon”, and for the first time since World War II, this blue moon will be visible nearly all over the world.

There are many origin stories on how a blue moon got its name. Many cultures around the world, particularly agrarian indigenous cultures, give names to full moons which correspond to certain events or seasons and each occur within a certain month, such as the “Harvest Moon” that just passed on October 1st. Considering that a complete lunar phase takes 29.5 days to complete, it takes a total of 354 days to complete 12 cycles. However, this falls short of the 365/366 days of a complete calendar year. Hence, about every 2.5 years, a 13th full moon occurs which doesn’t really follow the cultural naming scheme, and thus is referred to as the blue moon.

An older definition of a blue moon states that the Blue Moon is the third full moon in a season which has four full moons. This is a slightly complicated definition for people who use the Gregorian calendar, as it relies on the astronomical seasons which take into consideration the equinoxes and solstices.

Some may wonder if the moon actually turns blue when the Blue Moon rises in the sky. The simple answer is no. It is merely another full moon which happened to occur a second time within a month. However, it will definitely add to the mystique of Halloween this year. It is definitely something for those whose celebrations are affected by lockdowns and quarantines due to COVID-19.


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