Why does the full moon seem larger in the evening as it rises over the horizon?

Question

Later in the night the moon doesn't seem to be as large in diameter. Could this be due to a magnifying effect of the atmosphere as it rises?

Answer 1

it's a well-known optical illusion.

Answer 2

No...it is actually..nothing more than an optical illusion.

When we normally look at distant objects..they appear very small...by comparison...when we see the moon coming up over the horizon..next to these distant objects....it makes it appear that the moon is enormous.

Now..when the moon gets higher in the sky...there's no longer any distant objects near it..so.it doesn't appear to be as big as it was near the horizon.

Try an experiment...hold a small object at arms length toward the moon when it's on the horizon..and measure the size of the moon.

Now use the same object..and again at arms length when the moon is higher in the sky.

There will be no difference in size.

You can try this another way...when the moon starts to come up...if you have a clear enough view of the horizon line..

turn..facing away from the moon....and...bend over!!..thats right..bend over and view the moon through your legs....and..the moon won't appear as big as it does when you face it.

Enjoy these experiments.

Answer 3

It is not actually larger, in fact, this is such a common misconception that it has earned the name the "moon illusion" (it also happens with the sun).  The reason for this has been unclear--though we know it is just an optical illusion.  The most accepted explanation is that at the horizon, there are objects (like trees and houses) with which you can mentally compare in size to the moon and sun.  In the sky, there are no such objects and they seem smaller.

Hope this answers your question

Chris

Answer 4

Nah, it's a normal optical illusion!  Try this, take a pencil and compare the pencil's eraser with the moon when it's on the horizon and when it's out by it's lonely self, later in the night, you'll see the size of the moon will be the same.