As you watch the full "Sturgeon" moon rising over the east-southeastern horizon at 8:30 p.m. Tuesday, you may experience an optical illusion that sky watchers have experienced since ancient times. This phenomenon is known as the "moon illusion" and it is also true for the sun whenever it hovers near the horizon.
Stargazers have known for thousands of years that a low-hanging moon or sun peeking through trees and houses or over mountain ridges looks unnaturally big and inflated.
At first, astronomers thought the atmosphere must be magnifying the moon near the horizon, but cameras showed that's not the case.
Another popular explanation for the illusion is that when the moon is rising or setting, distant trees and houses might make the moon seem bigger than it is.
However, airline pilots flying at high altitudes sometimes experience the moon illusion without any objects in the foreground.
Scientists believe that the moon-horizon illusion is a cognitive illusion, meaning that it is an illusion due to the processing of information in our brains.