3 Quotes by Carlton Pryor

Globular clusters are old and give us a limit on the age of the universe. The universe couldn't be younger than the oldest star cluster.

If you plot the distribution of clusters, you discover that almost all of them are on one side of the sky, concentrated in the constellation Sagittarius in the summer sky.

All the stars in a cluster are the same distance away, so you can compare brightness without having to worry about whether a star that appears faint is actually very bright but just far away.