Once In A Blue Moon, Tonight

A blue moon; Elvis and Sinatra sang a song about it, and bartenders named a cocktail after it. Trivial Pursuit includes a question about it, and beer makers incorporated it into their marketing plan. It’s possible that more people are familiar with a blue moon in modern references like these, rather than the science of a full moon and its presence twice in a calendar month or as an extra full moon in a season marked by equinoxes.

Though rooted in old science and folklore, a blue moon by its current definitions is a modern term with modern associations. Smart marketers have brought Blue Moon beer to mainstream consumers, and even have the distinction of holding their 20th anniversary on tonight’s blue moon.

The turn of phrase “once in a blue moon” has the colloquial distinction of meaning something that happens very rarely, if ever. Even that meaning morphed over centuries from its earlier use, just as the astrological definitions did. Phrased more dryly, “when the moon turns blue” used to be similar to “when pigs fly” as reference to something very obviously absurd, like the moon being made of cheese.

In astronomical terms, blue moons aren’t really blue and are fairly frequent by this definition, occurring roughly every 3-4 years.

At the turn of the 20th century, Farmer’s Almanacs described a blue moon a bit differently than we do today, using a mess of twisted calculations to merge the Gregorian calendar with seasonal equinoxes, and defining a blue moon as any full moon that’s the fourth within a season, each season typically having three full moons. These kind of discrepancies, including the very non-scientific switch to our current understanding of a blue moon, are inconveniences at best, and at most are a jumping-off point for an interesting discussion.

“It’s something fun to talk about and it helps attract people to astronomy,” noted founding editor of Sky & Scope magazine, Charles Federer, Jr.

Tonight’s blue moon is a beautiful, natural reason to get outside and just spend time looking up. Drag your friends, gather your kids and grandparents, and talk about it; a pickup truck packed with blankets and parked in a field far from city lights works perfectly. Use it as a teaching tool to open a creative conversation with your kids about astronomy, and how it interacts with our arbitrary calendar.

Drag all of the modern references you can think of into your discussion, while you’re as far away from modern conveniences as you can get. Laugh with your friends about what fun can be blamed on a full moon; we’ve all used that excuse once or twice. Once in a blue moon is far too infrequent to step out of our modern lives and take notice of occurrences that predate modern everything.

[Image: IJG JPEG Library]

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