Why The Harvest Moon Appears to Shine On—For Days!

Where and When to See the Full Harvest Moon
September 11, 2019
Harvest Moon
NASA

 

The Harvest Moon, together with the Hunter’s Moon, are the year’s only full Moons that have official names.

Sure, in January you may hear things like, “Look for the full Wolf Moon this weekend!” But is that really the name of the January full Moon? It was, to Anglo-Saxons. But the Lakota Sioux would have retorted, “Nonsense! It’s not the ‘Wolf Moon.’ It’s the ‘Moon of Frost on the Teepee’!” To which the Cheyenne would have said, “You’re both wrong. It’s the ‘Hoop and Stick Game Moon’!”

So any reference that tries to definitively call any particular month’s full Moon by some specific name is choosing to adopt the traditions of some particular group of people and ignore all of the others. Except these two: the Harvest and the Hunter’s.

The Harvest Moon Definition

Astronomically, the Harvest Moon is the full Moon closest to the autumnal equinox (and things really are being harvested right around now).

So, the Harvest Moon isn’t always in the same month. It can fall in September or October. This year, it’s in September. (See the Full Moon Guide for September.)

When to Watch the Harvest Moon

  • Start watching as twilight deepens on Friday. There’s the almost-full Moon low in the east.
  • On the next night, Saturday, it’s there again, perfectly full.
  • On Sunday, you must wait a few minutes, almost for full darkness—but then up pops the almost-full Moon.

Why the Harvest Moon Shines On

Why does it seem as though there are several full Moons night after night?

  • First, note that full Moon near an autumn equinox rises closer to the time of sunset, so there’s not much time between sunset and moonrise.
  • Second, the Harvest Moon rises only 20 or 25 minutes later each night. Typically, the full Moon rises about one hour later each night.

Give this, the full Moon will appear to rise during or near twilight for several days before and after the full Moon. See your local Moonrise times.

It will seem like there are several full Moons – for a few nights in a row – around the time of the Harvest Moon.

You can’t get rid of this full Moon! It’s the relative who came for dinner.

You can see why this is called the Harvest Moon, too. Just when the farmer runs out of daylight to finish the harvesting chores, the full or nearly full Moon shines down from the sky night after night to help out with extra light. This doesn’t happen at any other time.

It’s the polar opposite of the full Moons of February, March, and April. Then, you’ll see moonrise at sunset on one night, but wham!—there’s a 1½ hour delay until the next night’s moonrise. And another 1½ hour delay the night after that. Result: A rising 7:00 p.m. full Moon is followed, just 2 nights later, by the absence of moonlight until 10:00 p.m.

The bottom line—and the whole point of this, of which relatively few people are aware—is that the Harvest Moon is an effect rather than a visual oddity.

The Harvest Moon is a study in lunar behavior, not appearance.

Read more about why this all happens in “Shine On, Harvest Moon!”

About This Blog

Welcome to “This Week’s Amazing Sky,” the Almanac’s hub for everything stargazing and astronomy. Bob Berman, longtime and famous astronomer for The Old Farmer’s Almanac, will help bring alive the wonders of our universe. From the beautiful stars and planets to magical auroras and eclipses, he covers everything under the Sun (and Moon)! Bob, the world’s mostly widely read astronomer, also has a new weekly podcast, Astounding Universe!

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