A Blue Moon Is Coming July 31, And It Won’t Be Back Again For Another Three Years

The inspiration for a clichéd saying, the famous “Blue Moon,” will rise over much of the world on July 31, and we won’t see another one until 2018.

The cliché has lived up to its name.

To be technically accurate, though, the Blue Moon as we understand it is kind of a misunderstanding, Space.com reported.

Earth gets its extra full moon because the lunar and calendar months aren’t quite the same length. At 29-and-a-half days, the lunar month is shorter than every one except February. These extra days add up until, eventually, we get a 13th in that special year.

A bit of confusion with the definition of the lunar event, which falls on July 31 and offers the month its second full moon, led to our current belief about what it is exactly. A season lasts generally three months, and each three months should have only three — when it has four instead, the third (and not the fourth, for some reason) is dubbed the extra.

Back in 1946, a magazine article in Sky & Telescope tweaked this definition a bit — the writer described it as the second full rising in one month. And this July, we’ll be treated to another on the 31; the last one was on the 2.

This event is actually pretty rare, occurring once every 2.7 years, and we won’t catch another until 2018. The last time we were treated to the sight was August, 2012. Luckily, it doesn’t matter where you live — everyone will be able to see it come Friday. It will occur when the sun, Earth, and moon fall into a single file, and that happens at the same time everywhere, no matter where the satellite is in the sky.

The so-called Blue Moon isn’t blue at all, either. Actually, it has many other names (Sturgeon, Green Corn, Grain, and Red) that coordinate with natural events on Earth, according traditions both from Native American cultures and Europe.

The planetoid is sometimes blue, of course, though whether it’ll take on the hue on July 31 remains to be seen. Smoke or dust particles floating around the atmosphere are usually to blame for that, CNN added. The cause is usually a volcanic eruption.

That’s what happened in 1883. Krakatoa erupted and for years afterward, it took on a bluish hue. The sunsets were also vividly red. In 1950, it took on the pretty color in Scotland — the smoke from forest fires in Canada caught in the clouds and the light from the Royal Observatory’s satellite traveled through it at just the right time.

Given that this event only occurs every now and then (hence the cliché), when July 31 rolls around, make sure to step outside for a bit to see it. Maybe something unusual will happen while you’re out enjoying the sight.

[Photo Courtesy Bruno Vincent / Getty Images]