Sidney, a Jewish scientist, wanted to know where the sun went after it set. He went around asking other scientists, but they didn’t know either. Pretty soon he had the whole of his science department trying to figure it out. They puzzled over it for a long time but they couldn’t come up with an answer. In fact, they sat up all night thinking about it until it finally dawned on them.
From Oy! The Ultimate Book of Jewish Jokes, by David Minkoff