M5 - Globular Cluster in Serpens

Messier 5 (NGC 5904) was first seen by Kirch in May 1702 and Charles
Messier found it independently in May 1764. He described it as a round
nebula which "doesn't contain any stars". M5 is thought to be one of
the oldest globular clusters - 13 billion years - and one of the
largest with a diameter of 165 light years.

http://www.martin-nicholson.info/ten...allenge/m5.htm