For the first time since 1990, and it won’t happen again until 2028, a ‘Blue Moon’ will appear on New Year’s Eve. The so-called ‘Blue Moon’ (a full moon) appears roughly every 2.7154 years, but for it to fall on December 31st is rare.
There will also be a partial eclipse of the moon, making the day doubly spectacular.
The definition of a ‘Blue Moon’ varies and has changed recently, well, 1946, but that was discovered to be an error, but not until 1999.
The most popular definitions are:
When calculating the dates for Lent and Easter, the Clergy identify the Lent Moon and it is thought that historically, when the moon’s timing was too early, they named an earlier moon as a “betrayer moon” (belewe moon), thus the Lent moon came at its expected time.
In popular folklore, each moon was given a name according to its time of year. A moon which came too early had no folk name and was therefore called a blue moon.
The Farmers Almanac defines a ‘Blue Moon’ as an extra full moon that occurs in a season, one season normally being three full moons. If a season had four full moons, then the third full moon was named a ‘Blue Moon’.
A ‘Blue Moon’ was classified as the second full moon in a calendar month, stemming from an interpretation error made in 1946 that was only discovered in 1999.