Two galaxies go into a bar every night. The first night they were both immaculately dressed, but the second night one's shoes were dirty and the other had lost his tie. Next night one’s jacket was torn and the other’s hair was unkempt. Each successive evening their appearances had deteriorated somewhat and after a week of this the barman was very curious.
“Excuse me gentlemen”, he said, “but I can’t help noticing that you are steadily becoming less well presented, what’s going on?”.
“It’s very simple”, replied one. “Each night we’re Messier objects”.