Asteria — interactive night sky map
Messier 39 is a open cluster in the constellation Cygnus with an apparent magnitude of 4.6, spanning about 20 arcminutes. Under dark skies it can be spotted with the naked eye.
It is best placed in the evening sky around August. It is visible from the whole northern hemisphere and from southern latitudes down to about 42°S. It is circumpolar (never sets) north of latitude 42°N.