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Bill Nye: Once in a Mega-Moon

Bill Nye: Once in a Mega-Moon

Author: Bill Nye

This tutorial from Bill Nye explains why the moon appears smaller when it's higher in the sky and presents an experiment that proves that it's all in your head.

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Once in a Mega-Moon

The Moon is big. Not as big as the Earth, but still pretty huge. It would take you 5 solid days to drive a car all the way around the Moon. (And forget about stopping off for a hamburger.) Since its closer to us than any other large body in space, the Moon appears big in the night sky, too. Sometimes the Moon looks bigger than usual, but it’s always the same size. Try this:

What You Need:

1. A clear day or night when there’s a bright Moon in the sky 
2. A stiff card or piece of cardboard and a pencil, pen, or marker

What You Do:

1. When the Moon is low, just above the horizon, hold the card at arms length and mark the diameter (from edge to edge) of the Moon. 
2. Try looking at the Moon again a few hours later when the Moon is higher in the sky. Hold up your card and compare the lines. Does the Moon measure up as bigger or smaller than before?

What’s Happening?

As the Moon rises higher, it will seem smaller than it did while it was near the ground! Some scientists think that when the Moon is low in the sky, our brains automatically compare it to things on the ground that we already know are plenty big, like trees and houses. These scientists figure that since the Moon looks bigger than those already-big things, we think it’s especially huge when it hangs close to the horizon. Check out the mega-sized Moon sometime. Your brain goes right to it.


Once in a Mega-Moon

Here's the same Home Demo in convenient PDF form!