"Moshe was compared to the sun, and Yehoshua was compared to moon" (Tractate Bava Basra 78A)
Yossi: Yossi, what is it called when the moon is just a curve?
Pinny: It's called a crescent moon, Pinny. Why do you ask?
Yossi: Well, Yehoshua was just like the moon because he reflected everything Moshe taught him... just like the moon reflects the light of the sun.
Pinny: I also want to be a moon, Yossi, but I don't listen as well as Yehoshua to our Rebbe. So, I thought, maybe I won't be a full moon like Yehoshua, but I'll at least be a crescent.