Have you ever noticed how big the moon looks when it's rising? But not so big when itís high in the sky? The moon's enormous "horizon" size is an illusion caused when it's seen low near objects like buildings and trees. When it's high in the sky, there isn't much of known size nearby to compare it to.

Test the illusion for yourself: Go outside to observe a rising full moon with a sheet of paper and some rubber bands. Roll the paper into a tube and, using it like a telescope, adjust the size of the tube until the moon just fills its width. Use the rubber bands to keep that tube size.

After the moon moves higher in the sky, check it again, first without the tube, then through the tube. You'll see that the moon stays the same size - even though your eye sees the illusion.

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