This misinterpretation gained steam after it was referenced on a popular radio program StarDate, in 1980, and in a question in the Trivial Pursuit game in 1986. This idea actually started in 1946, when, in his article Sky and Telescope, James Hugh Pruett misinterpreted the concept of the fourth full moon in a season being a blue moon, from the Maine Farmer’s Almanac, stating instead that the second full moon of the month was called a blue moon. You are probably more familiar with the idea that a blue moon is the second full moon in a calendar month. When the idiom appeared in the 19th century, in the publication of Real Life in London by Pierce Egan, once in a blue moon meant 'close to impossible' or 'rarely.' You can see this insert from the story, “How’s Harry and Ben? – haven’t seen you this blue moon.” Nevertheless, the phrase that we love to use in our everyday talks did not really appear until much later. You can find the first recorded use of the phrase, or something similar, in an anti-clerical pamphlet published by William Roy and Jeremy Barlowe around 1528 with the phrase 'if they say the moon is, it must be true.' The expression would be used in situations to imply a fool or gullible people will believe just about anything. There are multiple definitions of a Blue Moon Source: NASA In 2020, on Halloween, there was a blue moon. Occasionally two full moons will fall within the same month. These celestial events happen on average once every 2.7 years. This moon is traditionally known as a 'blue' moon. On a violent night in the murky streets of San Francisco, a cryptic message becomes key to unraveling a gruesome investigation.

Twice in a blue moon