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Speaker 1: Welcome to brain Stuff, a production of I Heart Radio,

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Speaker 1: Hey brain Stuff Lauren Bogobam. Here in nineteen fifty four,

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Speaker 1: a young Elvis Presley used the country standard Blue Moon

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Speaker 1: of Kentucky to help kickstart his career. By then, blue

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Speaker 1: moons had become a fixture in popular culture. This is

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Speaker 1: still the case today. Just look at blue Moon brand

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Speaker 1: beer or single blue Moon by back. But just because

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Speaker 1: a term is widely employed doesn't mean it's widely understood.

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Speaker 1: If you've ever wondered what blue moons are in the

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Speaker 1: astronomical sense of the phrase, this episode is for you.

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Speaker 1: The term blue moon dates back to at least the

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Speaker 1: sixteenth century, and since then it's been given several different definitions,

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Speaker 1: many of which are contradictory. At first, blue moon was

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Speaker 1: slang for something that was flat out impossible, but over

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Speaker 1: time the meaning of this idiom changed to refer to

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Speaker 1: things that were either rare or highly unlikely. This, explained

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Speaker 1: means the modern phrase once in a blue moon, and nowadays,

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Speaker 1: when a person says that something occurs once in a

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Speaker 1: blue moon, they mean it doesn't happen very often, but

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Speaker 1: that it's not impossible. And in the eighteen hundreds, this

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Speaker 1: expression received yet another meaning. It takes the moon twenty

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Speaker 1: nine point five three days to complete a full rotation

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Speaker 1: around the Earth. In the process, the appearance of the

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Speaker 1: moon goes through all of its phases, from new to full. Therefore,

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Speaker 1: each calendar quarter or season spring, summer, fall, and winter

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Speaker 1: typically sees three full moons apiece, assuming one full moon

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Speaker 1: each month, but every so often a single season will

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Speaker 1: get an extra moon, and during the nineteenth century some

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Speaker 1: stargazers began to refer to the third full moon in

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Speaker 1: a season, which sees four of them altogether, as a

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Speaker 1: blue moon. The Main Farmer's Almanac popularized this definition in

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Speaker 1: time for a quick aside. You might be wondering why

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Speaker 1: the third full moon in a season with four was

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Speaker 1: singled out here. Why didn't people just call that fourth

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Speaker 1: one the blue moon? The answer boils down to naming conventions. Again,

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Speaker 1: most years see twelve full moons in total. Many cultures

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Speaker 1: have given names to those that appear at specific points

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Speaker 1: in the year. For example, in some American traditions, the

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Speaker 1: last full moon of the winter is called the worm moon.

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Speaker 1: If the winter season in any given year were to

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Speaker 1: see four full moons, calling the final one a blue

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Speaker 1: moon would disrupt this linguistic status quo right then back

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Speaker 1: to the Main Farmers Almanac. From ninety two to nineteen

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Speaker 1: fifty seven, this now defunct publication championed this definition of

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Speaker 1: blue moons. The waters were further muddied in nineteen forty six,

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Speaker 1: but when an astronomer named James Hugh Pruett wrote an

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Speaker 1: article about blue moons for the magazine Sky and Telescope.

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Speaker 1: In it, he misinterpreted an excerpt from the nineteen thirty

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Speaker 1: seven edition of the Main Farmers Almanac. This led him

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Speaker 1: to conclude erroneously that a blue moon is the second

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Speaker 1: full moon in any given calendar month. Pru It's blunder

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Speaker 1: went on to have a life of its own. One

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Speaker 1: episode of the radio program started repeated his mistaken idea

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Speaker 1: about what a blue moon is. After that, this new

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Speaker 1: definition turned up on a trivial pursuit card and in

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Speaker 1: a children's nonfiction book. Yesterday's missprint can become tomorrow's accepted wisdom.

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Speaker 1: Most people now subscribe to prue It's definition. Thanks to

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Speaker 1: this kerfuffle, astronomy fans are left with two competing schools

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Speaker 1: of thought about what constitutes a blue moon. The rival

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Speaker 1: definitions now go by different names. The third full moon

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Speaker 1: in a season with four of them is called a

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Speaker 1: seasonal blue moon. Meanwhile, the second full moon in a

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Speaker 1: calendar month is called a monthly blue moon. The latter

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Speaker 1: phenomenon occurs once every two to three years. You'll note

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Speaker 1: that neither definition has anything to do with the Moon's

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Speaker 1: actual coloration. By virtue of its surface geology, Earth's natural

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Speaker 1: satellite usually looks gray, and during lunar eclipses, the refraction

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Speaker 1: of sunlight can give it a rusty red appearance. But

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Speaker 1: does the Moon ever turn blue? Well, yes, but only

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Speaker 1: under certain circumstances. In the past, there have been documented

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Speaker 1: instances of smoke and ash from massive forest fires and

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Speaker 1: volcanic eruptions, sending up particles into the atmosphere that filter

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Speaker 1: out red light. When this happens, the moon takes on

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Speaker 1: a blue appearance. In short, if you ever see a

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Speaker 1: moon that is literally blue, it's because something very destructive

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Speaker 1: is happening down on Earth. Today's episode is based on

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Speaker 1: the article why a blue Moon's Not really blue on

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Speaker 1: how Stuff works dot Com, written by Mark Vancini. Brain

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Speaker 1: Stuff is production of by Heart Radio in partnership with

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Speaker 1: how Stuff Works dot com and it's produced by Tyler

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Speaker 1: Clay Or more podcasts, My Heart Radio, visit the i

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