The "Blue Flower Moon" Rises This Weekend | The Old Farmer's Almanac

The "Blue Flower Moon" Rises This Weekend


What's So Special About May's Full Moon?

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The Full Flower Moon arrives this Saturday night, May 18. And while this one will be a very special full moon for a few reasons, which we’ll get to in a minute, it’s also an unusual Blue Moon. What does this all mean? Here’s everything you need to know.

A Seasonal Blue Moon

This year, May’s full moon—which the Almanac calls the “Full Flower Moon”—is also a “Blue Moon.”

You’ve more than likely heard this term before, but what does it mean, exactly? Believe it or not, Blue Moon is a fairly modern coinage and there are actually two different definitions. The original defines a Blue Moon as the third full Moon of four full Moons to occur in one season, while the other defines it as the second full Moon to occur in one calendar month.

In the case of this weekend’s Blue Moon, it’s the former: the third full Moon of four that will happen in the spring season. This phenomenon occurs once every two to three years—or, “once in a Blue Moon,” I suppose!

Note that the Moon won’t look blue or anything… It’s really just a fun fact and a calendar anomaly for us Moon lovers.

Read more about Blue Moons in my post, What is a Blue Moon?

May Full Moon Names

Full Flower Moon… Blue Moon… The full Moons have many names these days, and you shouldn’t be surprised if you hear some announcer on TV say, “go out tonight and see the Milk Moon!” or yet another name. 

There really isn’t an astronomical origin to most Moon names. How did this start? If we go back in history, people did not record time by using the months of the Julian or Gregorian calendar. Many ancient peoples kept track of time by observing the seasons and lunar months, although there was much variability.

For some groups, the year contained 4 seasons and started at a certain season, such as spring or fall. Others counted 5 seasons to a year. Some defined a year as 12 Moons, while others assigned it 13. Certain people that used the lunar calendar added an extra Moon every few years, to keep it in sync with the seasons. 

Here is just a sampling of the many Moon names!

  • The Lakota Sioux called this, the Moon of the Shedding Ponies.
  • The Laguna tribe referred to it as the Loam Plant Moon.
  • It was the Flower Moon to the Algonquins.
  • But not everyone in that tribe liked that label. Some of them called this The Corn Planting Moon and yet others insisted we were all gazing at The Milk Moon.
  • Many dairy-loving Colonial Americans liked that one, so they also called the May Full Moon the Milk Moon.
  • But other Colonists called it the Mother’s Moon, and still others the Hare Moon.
  • To the Cheyenne, this was the Moon When the Horses Get Fat.
  • And with all this, we can’t blame the Zuni tribe for throwing up their hands and calling it the Moon With No Name.

Here at The Old Farmer’s Almanac, we tend to rely on the Algonquin name, Flower Moon, due to our regional overlap during Colonial American times.

Read more about the Origin of Moon Names.

What’s Special About May’s Moon?

Anyway you slice it, May 18 brings the second-lowest full Moon of the year. 

All full Moons are low during the first hour after they’ve risen, of course, but when next weekend’s moon reaches its highest point in the sky at midnight, it will still only be one third of the way up the sky.

This is actually a good thing.

That’s because people most notice sky-objects that are close to eyesight level,  and relatively few crane their necks to look straight up. 

So next weekend’s full moon will attract attention.

Moon and Jupiter Conjunction

Adding to its conspicuousness, if you look at it around midnight you’ll see the sky’s brightest “star” to its lower left.  This is the planet Jupiter.  Meaning, the Moon and bright Jupiter will be in conjunction, only 7 degrees apart. The pair will cross the night sky together, visible until just before sunrise.

If it’s cloudy Saturday and you have insomnia the next night, check out the moon on Sunday night after around 2 a.m.—and now it will hover between Jupiter and less-brilliant Saturn. Very cool.

It’s a noteworthy accomplishment for a body with either too many names or no name at all!

See the Almanac’s May Moon Guide for more information on Moon phase dates, times, facts, and folklore.