The Castaway Cluster

The open star cluster NGC 6520, the "Castaway Cluster", and the dark foreground nebula Barnard 86. Credit: NOAO

The open star cluster NGC 6520, the “Castaway Cluster”, and the dark foreground nebula Barnard 86. Credit: NOAO

The Castaway Cluster, catalogued as NGC 6520, is located just above the spout in the “Teapot” of Sagittarius. This is a rich region of the Milky Way containing many gas clouds and star clusters, including the Lagoon and Trifid Nebulae. NGC 6520, a tiny jewel of a cluster, is often forgotten amongst these more famous sites


NGC 6520 is easy to find… just 3 degrees or so north of Alnasl, the star at the tip of the spout in the Teapot. Just west of the cluster, in good sky, you can also see the conspicuous dark nebula Barnard 86.

Red circle marks the location of NGC 6520, above the “spout” of Sagittarius

This open cluster is only 800 million years old and contains many hot blue stars. Within the field of view, you will also see bright red stars that are likely not associated with the cluster but simply share the same line of sight.

The Castaway Cluster is some 5,300 light years from Earth. Its 60 or so stars span 8 light years. On a good night, you’ll see perhaps 15-30 of these stars in a small scope.

NGC 6520 is also a distant cluster. That means it appears quite tiny in our skies. While you can see it in binoculars, you’ll need a telescope with at least 150-200x to resolve this tight family of fairly new stars. The dark splotch of Barnard 86 is located between the cluster and the bright star to the west. Try averted vision… you may see more dark nebulae.

The Castaway Cluster was so named by astronomy writer Stephen J. O’Meara because it looks like a tiny island in a tempestuous sea of stars. It reminded him of the story of the castaway Robinson Crusoe, shipwrecked on a small island near the coast of Venezuela in 1659.

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