NGC 6946 is a large spiral galaxy, lying on the Cepheus – Cygnus border about two degrees southwest of the 3rd- magnitude star Eta Cephei. The galaxy is 11th magnitude, and appears nearly circular to the eye, measuring about 8′ in diameter.
Many observers find this object difficult even with large telescopes, but personally I had no trouble seeing it with a 4.5-inch scope. I think that the key to success is observing from a location with very dark skies, because the galaxy has a low surface brightness even moderate light pollution will make it invisible.
Appearing in the same visual field, just 40′ northwest of NGC 6946 you will find NGC 6939, a dim open star cluster. Its eerie glow is partially resolved into stars at medium power, in the northern part of the cluster you will see three stars disposed in a triangle.
Apertures larger than ten inches will resolve the cluster completely, and NGC 6939 takes on a kite-like appearance with brighter stars defining a kite shape.
Finder map – field width 15 degrees, stars to magnitude 9.5.