Welcome to brain Stuff, a production of I Heart Radio, Hey brain Stuff Lauren Bogobam. Here in nineteen fifty four, a young Elvis Presley used the country standard Blue Moon of Kentucky to help kickstart his career. By then, blue moons had become a fixture in popular culture. This is still the case today. Just look at blue Moon brand beer or single blue Moon by back. But just because a term is widely employed doesn't mean it's widely understood.
If you've ever wondered what blue moons are in the astronomical sense of the phrase, this episode is for you. The term blue moon dates back to at least the sixteenth century, and since then it's been given several different definitions, many of which are contradictory. At first, blue moon was slang for something that was flat out impossible, but over time the meaning of this idiom changed to refer to
things that were either rare or highly unlikely. This, explained means the modern phrase once in a blue moon, and nowadays, when a person says that something occurs once in a blue moon, they mean it doesn't happen very often, but that it's not impossible. And in the eighteen hundreds, this expression received yet another meaning. It takes the moon twenty nine point five three days to complete a full rotation around the Earth. In the process, the appearance of the
moon goes through all of its phases, from new to full. Therefore, each calendar quarter or season spring, summer, fall, and winter typically sees three full moons apiece, assuming one full moon each month, but every so often a single season will get an extra moon, and during the nineteenth century some stargazers began to refer to the third full moon in a season, which sees four of them altogether, as a blue moon. The Main Farmer's Almanac popularized this definition in
time for a quick aside. You might be wondering why the third full moon in a season with four was singled out here. Why didn't people just call that fourth one the blue moon? The answer boils down to naming conventions. Again, most years see twelve full moons in total. Many cultures have given names to those that appear at specific points in the year. For example, in some American traditions, the last full moon of the winter is called the worm moon.
If the winter season in any given year were to see four full moons, calling the final one a blue moon would disrupt this linguistic status quo right then back to the Main Farmers Almanac. From ninety two to nineteen fifty seven, this now defunct publication championed this definition of blue moons. The waters were further muddied in nineteen forty six, but when an astronomer named James Hugh Pruett wrote an article about blue moons for the magazine Sky and Telescope.
In it, he misinterpreted an excerpt from the nineteen thirty seven edition of the Main Farmers Almanac. This led him to conclude erroneously that a blue moon is the second full moon in any given calendar month. Pru It's blunder went on to have a life of its own. One episode of the radio program started repeated his mistaken idea about what a blue moon is. After that, this new definition turned up on a trivial pursuit card and in
a children's nonfiction book. Yesterday's missprint can become tomorrow's accepted wisdom. Most people now subscribe to prue It's definition. Thanks to this kerfuffle, astronomy fans are left with two competing schools of thought about what constitutes a blue moon. The rival definitions now go by different names. The third full moon in a season with four of them is called a seasonal blue moon. Meanwhile, the second full moon in a calendar month is called a monthly blue moon. The latter
phenomenon occurs once every two to three years. You'll note that neither definition has anything to do with the Moon's actual coloration. By virtue of its surface geology, Earth's natural satellite usually looks gray, and during lunar eclipses, the refraction of sunlight can give it a rusty red appearance. But does the Moon ever turn blue? Well, yes, but only
under certain circumstances. In the past, there have been documented instances of smoke and ash from massive forest fires and volcanic eruptions, sending up particles into the atmosphere that filter out red light. When this happens, the moon takes on a blue appearance. In short, if you ever see a moon that is literally blue, it's because something very destructive is happening down on Earth. Today's episode is based on the article why a blue Moon's Not really blue on
how Stuff works dot Com, written by Mark Vancini. Brain Stuff is production of by Heart Radio in partnership with how Stuff Works dot com and it's produced by Tyler Clay Or more podcasts, My Heart Radio, visit the i heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows. H