What is Messier 71?

Messier 71 is a rather unremarkable looking little cluster in the constellation Sagitta, but astronomers have puzzled over exactly what it is for many years.  It has characteristics of both an open cluster and a globular cluster.  The general consensus is, I believe, that it is a relatively young globular cluster (9 to 10 billion years old) with a loose grouping of stars.

Messier 71. ST80 on Vixen GP. 9x60 at ISO-1600

UPDATE: APOD posted an article featuring Messier 71 on December 10, 2014.