Trumpler 31 (Collinder 357) -- Open Cluster in Sagittarius
A Rarely Visited Open Cluster in Sagittarius
Trumpler 31, also named Collinder 357, is a quaint little open cluster adjacent to the impressive
Herschel 400, open cluster,
NGC 6520.  Trumpler 31 deserves more respect than it gets from
amateur astronomers. Once you have found the triangle of three stars that border the small
cluster, look closely and you will see the cluster’s dimmer stars forming a faint but grainy
background in the triangle (at least in a 110mm refractor on a good night).  The Milky Way star
field around Trumpler 31 is especially rich with plenty of star patterns providing extra beauty to
the little cluster.