1 Iki Piki: It's always interesting seeing the star patterns in a new system. Is that blurry patch of light a star?
2 Spanners: No, it's a globular cluster.
3 Iki Piki: How can you tell the difference?
4 Spanners: Star clusters are Messier.

Many star clusters are indeed Messier.

---

2016-06-18 Rerun commentary: Oh man. I almost want to edit the original annotation of this strip to take away the link that explains the joke. But I won't.

That way lies a deep, dark, Caldwell of revisionism and madness.