Science Buddies: "Ask an Expert"

i am just starting on my science fair project and i need lots of help.
my question is: Why does the moon appear larger sometimes?
i am wondering how to start my project off, and i need to know how to find out the angular diameter of the moon?

Hi,
I moved your post to the physical sciences forum, since I think the experts here can better help you.

Good luck!

Mostly, the reason the moon appears larger at time, especially when it is just rising or setting, is an optical illusion. Here is one web site that discusses it quite a lot: http://www.lhup.edu/~dsimanek/3D/moonillu.htm

This web site also talks about it a lot: http://curious.astro.cornell.edu/questi ... number=319. It even gives this simple method to measure angular distance, and explains what it is:

"There is an easy way to approximate angular distances when you look at the night sky. Hold your arm fully extended in front of you. Close your fist and look at it superimposed with the objects you are trying to measure the angular distance between. From one edge of your fist to the other is about 10 degrees. One knucle is about 2.5degrees, and if you open your hand, the full span of your hand from the tip of your thumb to the tip of your little finger is around 20 degrees on the sky. "

To demonstrate that the moon actually does not change size as it rises higher into the sky, you could just take a photograph of it just as it is poking up above the horizon, and then again after it is fully in the sky. Measure the size of this image on the photos.

I hope this helps.

Have fun.

Ed Neu
Buffalo, MN

I found this and thought it might help in testing your hypothesis:

"If you measure the moon with a ruler held at arm's length (a paper clip bent into the shape of a calipers will also work), you'll find it's always the same size no matter where it happens to be in the sky!" http://www.straightdope.com/columns/rea ... he-horizon

Best of luck,

Marc