What Is the Harvest Moon? (2024)

The Harvest Moon appears from September 16 to 18!TheMoon will appear full for about 3 days around this time, from Monday through Wednesday. Why does this phenomenon happen? Learn more—and shine on HarvestMoon!

When Is the HarvestMoon?

This year, the brilliantHarvest Moon first appears in the evening of Monday, September 16, before reaching peak illumination at 10:34 P.M. EDT on Tuesday, September 17, 2024.

One thing that sets the Harvest Moon apart from other full Moon namesis thatit’s not associated with a specific month, as the othersare. Instead, the Harvest Moonrelates to the timing of theautumnal equinox(September 22, 2024), with thefull Moon that occurs nearest to the equinoxbeing the one to takeon the name “Harvest Moon.” This means that the Harvest Moon can occur in either September or October, depending on how the lunar cycle lines up with the Gregorian calendar.

The Harvest Moon does typically occurin September, taking the place ofthe full Corn Moon. However,it occasionally lands in October instead, replacing the full Hunter’s Moon.

Why Is it Called the HarvestMoon?

For several evenings, the moonrise comes soon after sunset. This results in anabundance of bright moonlight early in the evening,which was a traditional aid to farmers and crews harvesting their summer-grown crops. Hence, it’s calledthe “Harvest”Moon!

There are just a little over 12 complete Moon cycles every year, on average (there being about 29.53 days in a synodic month).The Harvest Moon isn’t like the otherMoons.

• Usually, throughout the year, the Moon risesan average of about 50 minutes later eachday.
• However, for the few nights around the Harvest Moon, the Moon seems to rise at nearly the same time: just 25 to 30 minutes later across the northern USA and only 10 to 20 minutes later farther north in Canada andEurope.

Additionally, theHarvest Moon rises at sunset and will rise very near sunset for several nights in a row because the difference is at a yearly minimum. It may almost seem as if there are full Moons multiple nights in arow!

More About the HarvestMoon

If interested, here is more detailed information about the Harvest Moon.(Warning: Scientific explanationbelow!)

The Moon’s orbital motion (combined with the larger orbit of the Earth around the Sun) carries it farther eastward among the constellations of the zodiac from night to night. At any one moonrise, the Moon occupies a particular place on the celestial sphere (the great dome of the heavens). Still, when the Earth turns toward that point 24 hours later, the Moon has moved off to the east about 12 degrees, and it takes an average of 50 minutes longer for the Earth to rotate toward the Moon and for the Moon thus to “rise.” Think of it as a giant Slinky in which each loop, representing one lunar orbit of the Earth, advances the orbit a bit farther along the spiralpath. The result of all this is that the Moon doesn’t rise at the same time everyday.

However, around the date of the Harvest Moon, the Moon rises atabout the same time for several days in a row.Why? Remember that the zodiac is the band of constellations through which the Moon travels from night to night. The section of the zodiac band in which the full Moon travels around the start of autumn is the section that forms the most shallow angle with the eastern horizon. Because the Moon’s orbit on successive nights is more nearly parallel to the horizon at that time, its relationship to the eastern horizon does not change appreciably, and the Earth does not have to turn as far to bring uptheMoon.

The Moon may rise as little as 23 minutes later on several nights before and after the full Harvest Moon (at about 42 degrees north latitude), which means extra lightat peak harvest time near autumn. By the time the Moon has reached the last quarter, however, the typical 50-minute delay hasreturned.

At the start of spring, the opposite applies. The full Moon is in the section of the zodiac that has the steepest angle with respect to the eastern horizon. For several days bracketing the full Moon nearest the vernal equinox, the delay in moonrise is as much as 75 minutes (at 42 degrees northlatitude).

Here is another way of expressing what happens with the Harvest Moon: It is in this part of the zodiac that the Moon’s eastward (orbital) motion has its largest northward component. For observers in Earth’s Northern Hemisphere, the farther north an object is in the heavens, the longer an arc it makes across the sky, and the longer a time it is visible above the horizon. Thus, to say that the Moon is getting rapidly farther north each night around the time of the Harvest Moon is to say that, for northern latitudes on Earth, it will keep rising distinctly earlier than would otherwise be expected—nearly the same time as the nightbefore.

How nearly the same is “almost the same time” each night? This varies with latitude; the farther north you are, the shallower the angle of the zodiac is with respect to your horizon. In most of the United States and southern Canada, the Harvest Moon rises 25 to 30 minutes later each night. The effect is less noticeable the farther south you go. But going north makes the Harvest Moon moreextreme.

According to astronomy author Guy Ottewell, the idea of the Harvest Moon originated in Europe (average latitude about 50 degrees north), where the Harvest Moon rises only 10 to 20 minutes later each night. It must have seemed a boon that just when days were getting rapidly shorter, and the Sun seemed to go down all too soon, the Harvest Moon arrived to extend the hours that harvesting could bedone.

Chinese Harvest MoonTraditions

As a final note, I should add that it is not just Western civilization that has given special importance to the Harvest Moon. For Chinese people everywhere, this full Moon is the occasion for the Festival of the August Moon (the “August” is through a calendar discrepancy) or Mid-Autumn Festival (in some cultures, the equinoxes and solstices have been considered the middle of the seasons). This festival is celebrated with joyful games and the eating of “Mooncakes.” Read more about how other countries celebrate the HarvestMoon.

I remember vividly being invited to one such celebration and singing songs and playing my guitar to a circle of friendly faces in the light of the rising HarvestMoon.

Ever notice that the low-hanging Moon looks especially big near the horizon? It isn’t really significantly bigger. Learn more about thistrick of the eyecalled the Moon Illusion.

Find out what your Moon phase is tonight and when the next full Moon is.