When the size of the moon becomes enormous, it can make anyone wonder why the moon looks so big. This moon illusion when the moon is close to the horizon is called the Ponzo 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.
Be sure to read up on the supermoon so as not to confuse the two!
The Ponzo 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.