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The Basics
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• Although its size, structure, and appearance are much like M31 in Andromeda, NGC 7331 is more than 20x farther away... about 47 million light years... so it appears much smaller. So in dark sky, the elongated spiral of NGC 7331 fits nicely into your field of view even at high magnification.
• Like most NGC objects, William Herschel was the first to glimpse this galaxy. He believed he saw individual stars and structure. The spiral nature of NGC 7331 was first discerned by Lord Rosse with his giant reflector.
• At 10th magnitude or so, you will see NGC 7331 with a 4-inch scope, but you'll need at least an 6-8-inch scope and dark skies to reveal much structure. To see detail in this Sab-type spiral, breath deep and take your time.
• You'll find NGC 7331 just under the front leg of Pegasus, about 4 degrees northwest of eta Pegasi. Check your star map at RA22h37m, Dec +34d25m.
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A Deeper Look
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• This galaxy is some 130,000 light years across with roughly 300 billion suns of mass: much larger than the Milky Way.
• Like many large galaxies, NGC 7331 has a high-energy X-ray source at its core, likely caused by matter falling at high speed into a central black hole. And there are rings of newer stars near the nucleus of the galaxy caused by a burst of stars formation long after the galaxy formed.
• If you've got a 12" or larger scope, you may see a group of fainter galaxies lying nearby NGC 7331. This visual grouping is informally called the Deer Lick Group, of which NGC 7335 is the brightest at magnitude 13.3 or so. Like I said, you need a big scope!
• Here's a lovely image of NGC 7331 and other Deerlick galaxies. Of course, it will not look like this through your telescope, or any other telescope. A lot of serious post-processing was done to make this image.
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Bonus Object
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Perhaps the most famous collection of galaxies in this region of the sky is Stephan's Quintet, a faint set of five galaxies, four of which interact with each other at a distance of some 300 million light years. You'll need a big telescope to see this group, which lies only 1/2 degree to the southwest of NGC 7331. Here's a splendid widefield picture of the whole region, including NGC 7331.
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Personal View
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At the beginning of the movie "It's A Wonderful Life", there is a scene featuring a conversation between two angels speaking in heaven. It turns out that the angels are represented by a photograph of two of the galaxies of Stephan's quintet, NGC 7320 and NGC 7318. Who say astronomy doesn't impart useful knowledge?
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