We’ve all seen a full moon looming large shortly after it rises, when it’s still hugging the horizon. Scientists say that large moon is an illusion, a trick your brain is playing. It’s called the moon illusion. Its causes aren’t precisely known, but the video below, from AsapSCIENCE, offers some explanation.
By the way, a large moon seen low in the sky might also appear red or orange in color. And that color is not an illusion. It’s a true physical effect, caused by the fact that – when the moon is low in the sky – you’re seeing it through a greater thickness of Earth’s atmosphere than when it’s overhead. The atmosphere filters out the bluer wavelengths of white moonlight (which is really reflected sunlight). Meanwhile, it allows the red component of moonlight to travel straight through to your eyes. So a low moon is likely to look red or orange to you.
Bottom line: A large moon seen near the horizon is an illusion. It’s called the moon illusion. The video in this post offers some explanation.