Very rarely. Almost never. “Once in a blue moon.”
The idiom denotes something that happens hardly ever. Yet blue moons are more than a figure of speech, as this month of August is about to prove.
August has graced us, gloriously, with one full moon already, the Sturgeon Moon. The month will soon offer an encore—a remarkable second full moon, known in folklore as a “blue moon.” It will be made even better, as it’s a supermoon. The largest of the year.
It’s no technical term, blue moon. Nor are they necessarily blue-colored—though they can be. Rather, the term arose from folklore.
As for supermoons, while they sound larger than life, they too exist, occurring because of the moon’s irregular orbit around Earth.
We will dig into both these moons.
What’s in a Blue Moon?
Here, we are dealing not with exact science, but folklore. “Blue moon” has disparate definitions, as folks are disparate creatures. And “lore” is—well, just that. There are several accepted definitions of a blue moon today.Firstly, the calendrical classification is what features this month. Those didn’t exist prior to 1946. Just as the name implies, calendrical blue moons denote the calendar month. When two full moons occur in one month, the second is a blue moon. They don’t happen every month—or every year—but they do happen.
Secondly, the seasonal blue moon is the older, more deeply-ensconced definition, with more historical clout. This is when four full moons fall within the solstice and equinox during the year—that is, within a season. There are typically three full moons per season. But when a seasonal blue moon occurs, there are four. Contrary to expectation, the third—not the fourth—is the blue moon.
How Rare Are Blue Moons, Really?
Almost never is somewhat an exaggeration. As one moon phase lasts 29.5 days—from new moon, to full, and back again—one can envision how this happens; in a calendrical blue moon, a full moon’s falling right at the start of the month will result in a second full moon, a blue moon, around month’s end. Calendrical blue moons happen once every 30 months, or two-and-a-half years. Rare, yes. But fictitious? No.Likewise, seasonal blue moons can result when full moons fall soon after either the equinox or solstice, allowing a fourth to squeeze in before season’s end. As mentioned above, the third moon is the seasonal blue moon.
A Supermoon, Too?
A feast for the eyes awaits on Aug. 30-31, for the blue moon is also a supermoon—and the largest full moon of the year.What’s a supermoon? It’s a full moon that appears both larger and brighter than normal, as it is actually closer to the Earth than usual.
This can only occur because the moon’s orbit around Earth isn’t exactly round; rather, it’s elliptical. So, sometimes the moon is actually closer to Earth than at other times. Its nearest point to the Earth is called its perigee; its point farthest away, its apogee.
How to Spot This August Blue Supermoon
Except for observers in the Arctic or Antarctic, full moons always rise in the east during the evening and set in the west at dawn, as full moons occur precisely because they are opposite the sun, from Earth’s perspective.The Calendrical Blue Moon Swirls in Modern Folklore
Before 1946, blue moons bore no calendrical reference. In typical folklore fashion, though, this notion spawned accidentally. An article published in the March issue of Sky and Telescope magazine in 1946, according to EarthSky, included an oversimplified description of the term, blue moon. Author James Hugh Pruett wrote:“Seven times in 19 years there were—and still are—13 full moons in a year. This gives 11 months with one full moon each and one with two. This second in a month, so I interpret it, was called Blue Moon.”
Mr. Pruett referenced the 1937 Maine Farmer’s Almanac. Yet, typically 13 full moons are needed in one calendar year, to have two in one month, EarthSky reported. By all accounts, there were only 12 full moons in 1937. So, Mr. Pruett was mistaken, apparently, yet his identification of blue moons lives on.
His inadvertent, yet understandable, oversight eventually got thrown into common usage, dredged up by EarthSky’s own Deborah Byrd to use on the radio series “StarDate.” It was later popularized in a children’s book by Margaret McLoone-Basta, “The Kids’ World Almanac of Records and Facts,” published in New York by World Almanac Publications in 1985.
Today, the calendar month blue moon is accepted, established beyond firm precedent. Not really correct, but really folklore for sure.
