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Blue Moon

Blue Moon–It May Not Mean What You Think it Means

The Moon is Center Stage in January and March!

The phrase “Blue Moon” has been used for over 500 years to indicate something unlikely or downright false. In 1528 a group of surly friars used the phrase  in a pamphlet criticizing Cardinal Thomas Wolsey-.

O churche men are wyly foxes… Yf they say the mone is blewe, We must beleve that it is true.

That’s the first written record and, given the times, I’m assuming those friars were burnt at the stake before they had a chance to see if the next full moon was blue or not. Common usage probably predates the written usage by a few hundred years. We still use the phrase “Once in a blue moon” to describe a rare event.

By one way of reckoning, 2018 starts with a bang with a blue moon in January, no full moon at all in February, and another blue moon in March. But that’s not the whole story!

Of course, you know the moon doesn’t really turn blue. At times, the moon—full or not– can seem blue because of clouds of dust or smoke or water vapor. Debris in our atmosphere can cause the moon to look red and when the moon is in eclipse, it will have a reddish, copperish glow. I suppose, it could even look green in the right situation, but the term Blue Moon hasn’t got anything to do with the color of our satellite and everything to do with the timing..

What’s a Blue Moon?

The time between full moons is 28 days meaning we have a full moon roughly every month. Trouble is our months are made up of 28-31 days because of a pesky wobble in the Earth’s rotation. (Weirdly, this wobble may be the echo of a nasty collision between Earth and something really big a few million years ago. This event didn’t quite end our planet but it did knock off a lot of matter which may have eventually coalesced into—you guessed it—the moon.)

Since we are accustomed to only 1 full moon per month, a second one is a little odd. The second full moon in a month was referred to as a Blue Moon back in 1946 and that definition has stuck.

By this definition, the blue moons in 2018 occur on January 31 and again on March 31. After that, its October 31, 2020 when the next one happens. Halloween in 2020—very cool!


The real definition—the one that goes back a great deal further than 1946—refers to an extra moon in a season. Going old school, we ditch those arbitrary months and divide the year into the times between solstices and equinoxes. This astronomical (and more certain) reckoning gives us 4 seasons.

[pdf-embedder url=”” title=”Reckoning Blue Moons”]

Generally, we have three full moons in each season. But because of that pesky wobble sometimes we get four—and—you guessed it again—that fourth full moon between an equinox and a solstice is called a Blue Moon. These happen about every 28 months so they aren’t crazy rare—but rare enough that the phrase once in a blue moon carries weight. Who knows what will happen in that amount of time. If you don’t believe that, just look back over the past 28 months and get back to me.

By this definition, the next Blue Moon is May 18, 2019, and then August 22, 2021, and then August 19, 2024. Using this reckoning makes it harder to calculate the next Blue Moon and it puts more distance between each one.

A Trilogy of Super Moons

Whether you count the January 31 full moon as a Blue Moon or not, it will definitely be the last of three Super Moons. A Super Moon is a full moon that occurs when the moon is at perigee–or the part of its orbit that brings it closest to earth. A Super Moon is noticeably larger in the sky than a regular moon. The first in the trilogy occurred on December 3. The January 1st full moon was really a super, Super Moon because the full moon occurred only 4.5 hours after the moon reached perigee—about as close as it ever gets. And the last Super Moon of 2018 happens on January 31.

Eclipse Alert

The January 31st moon will also be in eclipse for part of the earth. Not everyone will get to see the entire eclipse. Here is a link to an interactive map where you can find your location and get info on when and how much of the eclipse will be visible in your area.

No matter how you look at it, the moon situation in the first three months of 2018 is out of the ordinary. Don’t miss the free show—courtesy of your friendly neighborhood Universe.

Here’s a little moony mood music to listen to as you sip your glass of blue wine and stare up at the heavens.

What’s your favorite Moon watching song?

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