If I remember my math correctly: the moon is 30 arc minutes wide. there are 60 arc seconds in a arc-minute. 60 arc-minutes is 15 degrees in the sky, or one hour of rotation of the earth. M31 Andromeda galaxy is over 30 arc minutes. The arc function is basically used in telescopes and photography. If you are using charts, they have astro rulers you can use to determine distance. There are a few places to visit. Look for Observatories and Societies. They have answers. I hope I helped a little.