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The Moon Illusion: Why Does the Moon Look So Big Tonight?

The moon sometimes appears enormous, and this is because of the Ponzo Illusion.

Learn why the full Moon appears larger near the horizon—and why it's all an optical illusion

Written By: Bob Berman Astronomer

Who hasn’t turned down a road to confront a low, horizon-hugging Moon that seems absolutely enormous? Why does the Moon look so big? This is called the “Moon illusion.” Astronomer Bob Berman explains.

The Moon Illusion

The Moon looks especially large shortly after it rises while still touching the horizon. But it’s just the result of a trick your brain is playing.

Many people assume that this common effect is caused by our atmosphere magnifying the image, but the explanation for this optical illusion is far simpler:

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When the Moon is high overhead, it is dwarfed by the vast hemisphere of the heavens and appears to our eyes as a small disk in the sky. 

By contrast, when the Moon is low, it is viewed in relation to earthly objects, such as chimneys or trees, whose size and shape provide scale. Your brain compares the size of the Moon to the trees, buildings, or other reference points, and suddenly, the Moon looks massive! 

Yup, it’s that simple!

Next time you notice a gigantic Moon on the horizon, look again when the Moon is higher up. With nothing to compare the Moon to, it will look a lot smaller.

How does the Moon illusion differ from a “supermoon”? Read up on the supermoon so as not to confuse the two!

A “Moon dog” can also occur when the moon is low on the horizon; learn more about the phenomenon of a Moon dog.

Why Does the Moon Appear Orange When Low in the Sky?

When the Moon appears extra-large near the horizon, you may also notice that it seems more orange or red. This is where Earth’s atmosphere comes into play.

When the Moon is low in the sky, it is farther away from you than directly overhead. Because of this, the light being reflected off of a horizon-hugging Moon has to travel farther—and through more particles of air—to reach your eyes.

By the time we perceive this light, the shorter wavelengths of light (the “blue” ones) have been scattered by the air, leaving only the longer wavelengths (the “red” ones) to reach our eyes. Thus, to us, the bluish hues are filtered out, and the Moon takes on an orange tinge!

In contrast, when the Moon is directly overhead, its light doesn’t need to travel through as many air particles, and the blue wavelengths can reach our eyes.

The Moon Illusion: How to See Through It

Don’t believe your eyes? Here’s how to reduce the Moon from enormous to ordinary!

  1. Find a paper tube, like the kind that holds paper towels.
  2. Close one eye and look through the tube at the enlarged Moon. It will appear normal.
  3. Now close the eye in the tube and open your other eye. The Moon appears huge again.
  4. Observe the Moon with the tube when it’s high and again when it’s low in the sky. The Moon will appear to be the same size both times.

When will the Moon rise? See the Almanac’s Moonrise/set calculator and just type in your zip code!

And here’s a handy trick to know: “When Will the Moon Rise Today?” 

Moon
About The Author
Bob Berman

Bob Berman

Astronomer

Bob Berman is an astronomer, author, and science communicator with decades of experience making the wonders of the universe accessible and engaging. Known for his wit and insight, Bob has captivated a...
Read More from Bob Berman

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Comments

<span>K. S.</span> Sun, 11/09/2025 - 01:02
Moon illusion solved https://www.amazon.nl/Moon-Illusion-Solved-Complete-Analysis-ebook/dp/B0FYZL4CGF
<span>Anne</span> Sat, 05/25/2024 - 10:25
Very interesting Wouldn't the moon be farther away as it travels higher in the skY? ps I've been following a planet at night; the planet travels from west to east nightly~ then it goes northward and disappears behind the trees;
<a title="View user profile." href="/author/editors">The Editors</a> Thu, 05/30/2024 - 11:10

One would think that the Moon is farther from us when it is at its highest point in the sky than at the horizon, but actually it appears that the opposite is true. Scientists have found that, illusion aside, a full Moon looks about 1.5 percent smaller when it is at the horizon than when, in this example, it is right above us, at zenith, because to see the Moon at the horizon, we are first looking across the radius of Earth (about 4,000 miles) and then on into space to the Moon. When the Moon is at the zenith, we are looking straight from our location on Earth's surface into space to the Moon. (Note: The highest point of the Moon's arc, as it crosses the meridian, may not be directly overhead, depending on your location and date.) Hope this helps!

 <span>Paula</span> Mon, 03/09/2020 - 18:59
"Cold hearted orb that rules the night... we decide which is right. And which is an illusion." Thank you for linking this from the super moon article, for the info and also that homey yet somewhat surreal-looking photo.
<span>Abyhshhs Jxushx</span> Fri, 01/20/2023 - 15:01
Yeah it's not because the moon is closer lololololol, it's not closer at moonrise, farther at peak height, then closer again at moonset lolololol
<span>Jan Marie</span> Wed, 07/30/2014 - 16:23
During the 1st week of July a couple yrs ago I was staying at a Gulf of Mexico cabin. I woke up in the middle of the night and thought I was dreaming when I looked out and saw what I thought was a second sunset but quickly realized it was a moon-set. The moon was very large and red and spread a rosy path on the water. What caused this illusion?
<span>Pearson</span> Thu, 04/21/2022 - 07:30
South of the Equator the moon looks larger because it goes round at the shortest distance also the atmosphere acts like a Lens it’s curved therefore magnifying the Moon !.
<a title="View user profile." href="/author/editors">The Editors</a> Thu, 07/31/2014 - 09:33

As mentioned in the above article, when the Moon is near the horizon, it looks large. The lit part of the Moon is due to reflected sunlight. When the Moon is near the horizon, its reflected sunlight has to pass through more atmosphere than when it was higher. As a result, more of the shorter wavelengths (blue and green) get scattered, leaving the longer wavelengths, such as red light. (This happens at sunset, too.)

You might also see a red Moon (no matter where it is in the sky) if the atmosphere has a lot of particles, such as due to a fire, volcanic eruption, or pollution, because the particles also scatter more of the shorter wavelengths of light.

 <span>Spottless</span> Fri, 02/07/2014 - 23:03
I would like to view the Moon Illusion, take photograph of supet size moon. Ive only seen it 2 times ands was awestruck. When in 2014 can I see this moon? What can I use to photograph it to get the same effect. Thank you Thank you..what
<a title="View user profile." href="/author/editors">The Editors</a> Wed, 02/12/2014 - 16:05

The best time to see the Moon illusion is when the Moon is near the horizon, either rising or setting. The full Moon rises around the time of sunset, so that would be a good time to try the experiment. Photographs will show the same size Moon no matter where it is in the sky. Your eye, however, will interpret the Moon as getting smaller the higher it ascends in the sky. The next full Moon will be on Friday, February 14, 2014. The one after that, Sunday, March 16. Check here to see when the Moon will rise in your area: 

www.almanac.com/astronomy/rise/