The term blue moon, which has nothing to do with the color itself of our satellite, is nothing more than the succession of two full moons within the same calendar month, something that happens approximately every three years .
The fact that it is possible that there are two full moons in the same month is due to the fact that the full moon cycle is approximately every 29.5 days , so if the full moon occurs on the first or second day of that month , there is a probability that a second full moon will appear in the last days, what we would call a blue moon.
Does the moon look blue? No, it does not look blue. For the moon to turn bluish, it must be influenced by ash and smoke . For example, in 1883 the explosion of the Krakatoa volcano (Indonesia) caused its ashes to spread to the limits of the atmosphere. The ashes scatter the red light but allow other colors to pass through, hence the blue moon when passing through the ash clouds.
The next blue moons:
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October 2020
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March 2023
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May 2026
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December 2028
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September 2031
When did the term “blue moon” first appear?
The notion of a blue moon first appeared in writing in the 16th century, according to folklore expert Phillip Hiscock, a professor at Memorial University in Newfoundland, who has traced the meaning of the phrase through the centuries. “In English, the first use we have is of Cardinal Wolsey,” Henry VIII’s notorious adviser, “Hiscock said.” Cardinal Wolsey writes of his intellectual enemies who ‘would make you believe the moon is blue.’
Aside from the occasional blue-tinged moon that can occur through a volcanic ash cloud, moons almost always appear in shades of white to yellow, and so to call the moon blue was to declare an absurdity. “The phrase was kind of a metaphor for absurdity or impossibility,” Hiscock said.
From that moment on, the “blue moon” took a turn towards something less strict, in 19th century London; as part of the street lingo that equaled “a long time.” Although it was probably in use for a time, the lingo first appeared in an 1821 book about the London working class. “A man is quoting someone on the street in London saying, ‘I haven’t seen you this blue moon.'” The note reads: ‘Blue moon: this is usually meant to imply a long time.’
The next literary reference came in 1869, when, in an autobiographical account of a shipwreck survivor, a man wrote about “that indefinite period known as the ‘blue moon’ “. Seven years later, the phrase appeared again, this time without explanation . When talking about diet, a character in an 1871 book admits to eating “a fruit cake once every blue moon.”
The lack of explanation “clearly shows that, at least in Britain where these quotes came from, that phrase seemed to catch on in the middle of that century between the 1920s and 1970s,” Hiscock said.
