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

Learn Why the Moon Appears Larger on the Horizon

By Bob Berman
August 17, 2019
Moon Illusion

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 sometimes? This is called the “Moon Illusion!” 

The Moon Illusion

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

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

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!

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 to be more orange or red in color. This is where Earth’s atmosphere comes into play.

When the Moon is low in the sky, it is farther away from you than when it is directly overhead. Because of this, the light that’s being reflected off of a horizon-hugging Moon has to travel a farther distance—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 are able to 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.” 

Source: 

The 2005 Old Farmer's Almanac

Reader Comments

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During the 1st week of July a

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?

As mentioned in the above

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.

I would like to view the Moon

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

The best time to see the Moon

The Editors's picture

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/

When the "enlarged" moon is

When the "enlarged" moon is near the horizon, another way to negate this optical illusion: face away from the moon, then bend over and look at the moon between your legs. Lo and behold, the moon looks its usual size.

I have a question about a

I have a question about a smiling moon? In the northeast area of US I have been seeing alot of the smiling moon, what is that about?

The crescent moon looks like

The crescent moon looks like a smile in the winter and spring and like a backwards "C" in the summer and fall. This is related to the Moon's path, where the Sun is, and how and where it shines on the Moon.

I'm sorry. But I think this

I'm sorry. But I think this article is nonsense! Yes, our lens-shaped atmosphere has nothing at all to do with how the moon looks through its convex boundaries.

The article isn't Moon lore;

The article isn't Moon lore; it's written by leading astronomer, Bob Berman, director of Overlook Observatory in Woodstock (NY), director of Storm King Observatory in Cornwall (NY), founder of the Catskill Astronomical Society--and long-time astronomy editor of The Old Farmer's Almanac!