Q: Why are false teeth like stars?
A: Because they come out at night!
Explanation: When I was a kid, my dad had this neat trick that would always make us laugh: While driving, he would loosen his lower front teeth (dentures) and wiggle them in front of his lips, below his nose. We of course would giggle. These teeth were false teeth that replaced his original teeth. Every night he removed those false teeth to clean them. Yes, his teeth had to come out at night so he could clean them.
Stars also come out at night. In reality, they do not come out, they are always there, but we cannot see them because our star, the sun, makes it too bright for us to see the starlight that comes from very far away. To us it seems that the stars come out of their daytime hiding place.
This joke is funny because it plays with different meanings of come out: remove, like the teeth, and appear, like the stars.
Thinking about stars had me thinking about space and space travel and the moon…