Moon Illusion: A fun trick to try

How big is the moon really? Check out this family-friendly moon illusion.

Have you ever noticed how the moon always looks larger when it is close to the horizon rather than overhead in the night sky?

The moon appears larger when it is close to the horizon because you are unconsciously comparing it to foreground objects that are at or near the horizon. When the moon is higher in the sky, there is less likelihood of making such a comparison, so the moon appears to be noticeably smaller in size.

Interestingly, when you see the moon looming large near the horizon, you can make it instantly revert back to its “normal” size by looking at it through a cardboard tube (like the kind that aluminum foil or paper towels are rolled on). By looking through the tube, you are restricting your eye’s view to just the moon and excluding the surrounding landscape. The moon immediately shrinks to its normal size.

And incidentally, this illusion cannot be photographed. If you take a photograph of the moon when it appears “bloated” near the horizon and a second photo when it’s higher in the sky and much smaller, you’ll find upon developing the photos that both images appear exactly the same. If you ever see a photo of an overly large moon near the horizon, it was probably taken with a telephoto lens.

The moon can appear large whenever it is rising or setting, and the phase doesn’t matter. The illusion, however, is accentuated somewhat when the moon is at or near perigee (that point in its orbit closest to the Earth).

Print Friendly, PDF & Email

This article was published by the staff at Farmers' Almanac. Do you have a question or an idea for an article? Contact us!


Inline Feedbacks
View all comments

Plan Your Day. Grow Your Life.

Get money-saving tips, weather updates and more! Sign up today.