Harvest Moon Tonight: Strange Facts About September's Full Moon

September 2012 Full Moon Over Montebello, CA
SPACE.com reader George Garcia sent in his photo of the September 2012 harvest moon taken on Sept. 29, 2012, in Montebello, CA. (Image credit: George Garcia)

Summer is drawing to a close in the Northern Hemisphere, and a symbol of fall hangs in the sky tonight (Sept. 18) to help drive that fact home — the Harvest Moon.

The Harvest Moon is the full moon that falls closest to the autumnal equinox, which marks the beginning of fall in the Northern Hemisphere. This year, the equinox falls on Sunday (Sept. 22), and the moon reaches its full phase in North America overnight from Wednesday to Thursday (Sept. 18-19).

As it rises for several nights in a row at or near sunset, the moon will appear larger to observers near the horizon than it does high in the sky — a much-discussed phenomenon that is sometimes called "the moon illusion."

Our minds and eyes, used to seeing distant clouds on the horizon and closer ones a few miles overhead, believe that objects on the horizon are much farther away than objects higher in the sky. Since the moon is actually not farther away on the horizon, it appears larger.

This trick of the mind is true for the moon all year round, but it's particularly pronounced with the Harvest Moon because this full moon's path around Earth creates a particularly narrow angle with the horizon. As a result, the moon rises only 30 minutes later every day around the fall equinox, far below the average of 50 minutes.

Sometimes the moon turns orange, just like a fall pumpkin, because of clouds and dust in the atmosphere close to the horizon. So the Harvest Moon may hang low and large on the horizon tonight, like a colorful lantern.

Editor's note: If you snap an amazing photo of the Harvest Moon full moon or any other night sky target and you'd like to share it for a possible story or image gallery, please contact managing editor Tariq Malik at spacephotos@space.com.

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Elizabeth Howell
Staff Writer, Spaceflight

Elizabeth Howell, Ph.D., is a staff writer in the spaceflight channel since 2022. She was contributing writer for Space.com (opens in new tab) for 10 years before that, since 2012. Elizabeth's reporting includes an exclusive with Office of the Vice-President of the United States, speaking several times with the International Space Station, witnessing five human spaceflight launches on two continents, working inside a spacesuit, and participating in a simulated Mars mission. Her latest book, "Why Am I Taller?", is co-written with astronaut Dave Williams. Elizabeth holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, a Bachelor of Journalism from Canada's Carleton University and (soon) a Bachelor of History from Athabasca University. Elizabeth is also a post-secondary instructor in communications and science since 2015. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday. Mastodon: https://qoto.org/@howellspace