蜜桃恋人

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 Moon Appears Larger on the Horizon

Bob Berman
No content available.

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 鈥淢oon illusion.鈥 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:

Read Next

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 鈥渟upermoon鈥? Read up on the supermoon so as not to confuse the two!

A 鈥淢oon dog鈥 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鈥攁nd through more particles of air鈥攖o reach your eyes.

By the time we perceive this light, the shorter wavelengths of light (the 鈥渂lue鈥 ones) have been scattered by the air, leaving only the longer wavelengths (the 鈥渞ed鈥 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 蜜桃恋人’s Moonrise/set calculator and just type in your zip code!

And here’s a handy trick to know 鈥淲hen Will the Moon Rise Today.鈥 

Moon
About The Author

Bob Berman

Bob Berman, astronomer editor for The Old Farmer鈥檚 蜜桃恋人, covers everything under the Sun (and Moon)! Bob is the world鈥檚 most widely read astronomer and has written ten popular books. Read More from Bob Berman
 

More Like This

Comments

Annie Brinker (not verified)

14 years 7 months ago

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 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.

ninpolearner (not verified)

14 years 9 months ago

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; 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 蜜桃恋人!

Unfortunately, you should have consulted with a neuroscientist rather than an astronomer. This illusion has nothing to do with astronomy. It also has nothing to do with any comparison with other objects on the horizon. Rather, it is due to the fact that the human brain has evolved to judge the distance of objects in the sky based on the fact that they are always relatively close to the surface of the earth. Thus in normal experience. A bird directly overhead is much, much closer than one at the same height that appears near the horizon. As a consequence, a bird that occupied the same angular portion of our field of view at the horizon as one directly overhead would rightly be perceived as much larger. Because the moon is so far away, it does actually occupy the same angular portion of our field of view no matter where it is in the sky. Thus, at the horizon, our brain thinks it must be much larger. This also explains why it seems to follow us as we travel in a car.

Tough crowd! I love this site and what they have to say about the moon!