A “Blue Moon” is a fairly rare phenomenon that involves the appearance of an additional full moon over a certain period of time.
There are two definitions of this period, and one of them was born from a misunderstanding.
The first definition of a Blue Moon was the third full moon in a season of four full moons. Known as the seasonal Blue Moon, it occurs approximately every 2.7 years. Why is it the third full moon? Each season usually has three full moons, and some of them, for traditional and religious reasons, must occur at specific times of the year. Therefore, the “Moon before Christmas” is always one of the full moons preceding Christmas.
Another definition of a Blue Moon is the second full moon of the same month. This definition – one Blue Moon per month – has become popular in recent years due to a misanalysis of the original definition in an almanac.
So which definition is correct? Well, because language and word meanings are constantly evolving, take your pick. Both are commonly used today.
According to the old definition (first definition), the Blue Moon on Saturday May 21, 2016 is a seasonal Blue Moon. The next seasonal Blue Moon (when a season has four full moons) will occur in spring 2019. The third moon of this season will occur on May 18, 2019.
According to the new definition (second definition), the last Blue Moon occurred on July 31, 2015. The next monthly Blue Moon (the second Full Moon appearing in the same month) will occur on January 31, 2018.
By the way, a Blue Moon does not mean that it is blue – a Blue Moon only appears since the term once in a Blue Moon means very rare – but it is also possible to have the possibility of being a little blue during a full Moon (more explanation on this below)
The phrase “once in a blue moon” has been around for more than 400 years, according to Philip Hiscock, a folklorist at Memorial University of Newfoundland. In a 2012 article in Sky & Telescope magazine, he explained that the first use of the phrase was like saying the moon is made of green cheese – it indicates something so absurd. Saying “The moon is blue” is like saying “Black is white”.
The meaning may evolve to refer to something like “never” happening, according to Hiscock. “I’ll marry you when the moon turns blue” is like saying “I’ll marry you when…pigs can fly.”
But never say “never”. Because the Moon can also be pale blue, as it appeared in 1883 after the volcanic eruption of Krakatoa. Dust in the air acts as a filter, causing sunsets and the Moon to turn green and blue around the world. Other events such as wildfires and dust storms can also cause the moon to turn blue. As a result, the meaning of the phrase “once in a blue moon” changed from “never” to “rarely,” according to Hiscock.
We now have conflicting definitions of a Blue Moon.
The calendrical reference to the concept of a Blue Moon comes from a now-defunct Maine Farmers’ Almanac from the mid-1800s. On the August 1937 newspaper page, the almanac explained that the Moon “usually appears in a full circle 12 times a year, three times a year. times per season. However, sometimes there will be a year with 13 full moons per year, not the usual 12. And this extra full moon also means that each of the four seasons will have four full moons instead of the usual three. »