Who hasn't turned down a road to confront a low, horizon-hugging Moon that seems enormous? This is the famous “Moon illusion.”
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.
Want to make the Moon illusion vanish?
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.