In Friends season 2, episode 1, at 18:35, Ross makes a joke about Monica's new haircut. He says "I think it's a ten". Chandler then does some jokes as well, such as "You could be caught between the Moon and NY city" and "I know it's crazy but it's true".
You can check the jokes here, at 2:55.
I don't get the double meaning. Can anyone explain the jokes?