Discovered by William Herschel in 1784.

NGC 7331 is the dominant member of the Deer Lick Group of galaxies.  Located in Pegasus the galaxy lies at a distance of 49 million light years from our position.  This galaxy was among 18 galaxies included in the Hubble Extragalactic Distance Scale Key Project.  Cepheid variable stars were observed in these galaxies to determine galactic distances.  NGC 7331 is the large spiral galaxy in the image above. Four other galaxies are prominent in the image.  Red shift measurements indicate these are background galaxies and not satellites of NGC 7331.  An image showing the designations of these galaxies may be viewed here.

¹http://www.seds.org/messier/xtra/ngc/n7331.html