Moon Illusion: Why Is the Moon So Big Tonight?

Ponzo Illusion: The Big Moon Effect

By Bob Berman
September 5, 2016
Moon Illusion

When the size of the Moon becomes enormous, it can make anyone wonder why the Moon looks so big. This is the “Moon Illusion.” 

Who hasn’t turned down a road to confront a low, horizon-hugging Moon that seems enormous? 

Many people assume that this common effect is caused by our atmosphere magnifying the image, but the explanation is far more simple.

When the Moon is high overhead, it is dwarfed by the vast hemisphere of the heavens. 

By contrast, when the Moon is low, it is viewed in proximity to earthly objects, such as chimneys or trees, whose size and shape provide scale.

It’s that simple!

Be sure to read up on the supermoon so as not to confuse the two!

The Moon Illusion: How to See Through It

Here’s how to reduce the Moon from enormous to ordinary!

  • Use a paper tube like the kind that holds paper towels.

  • Close one eye and look through the tube at the enlarged Moon. It will appear normal.

  • Now close the eye in the tube and open your other eye. The Moon appears huge again.

  • 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.

If instead you’re eager to see the Moon at its biggest size, look at our page “When Will the Moon Rise Today?” as well as our Full Moon Finder so you can catch it when it’s fullest and closest to the horizon.

This article was originally published in 2011 and has since been updated.


The 2005 Old Farmer's Almanac

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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:

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!