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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
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Close-up of spiral galaxy
NGC 6946. Gemini
Observatory/Travis
Rector [larger image]
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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, enclosing the now resolved and fairly rich cluster of uniform stars.
Finder map - field width 15 degrees, stars to magnitude 9.5.
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Surface brightness - The measure of an object's brightness per unit area. In most cases surface brightness is expressed as stellar magnitudes per square arcminute or arcsecond. Let's say that you observe a galaxy that has a surface brightness of 13. This means that each square arcminute of the galaxy is as bright as a 13th-magnitude star.
