NGC 6539, or GCL 85, is a globular cluster of stars in the constellation Serpens.

[6][7] This cluster is visible with a small amateur telescope, having an apparent visual magnitude of 9.6 and an angular size of 6.9″.

[2] This cluster is located in the outer parts of the Galactic bulge.

There is a large dark cloud complex located in the fore of this cluster, causing reddening from extinction.

Compared to other globular clusters, NGC 6539 is considered metal rich, indicating that it has a relatively higher abundance of elements more massive than helium.