NGC 7331, mag. +9.5, is a spiral galaxy about 50 Million light-years distant in the constellation Pegasus. It's the brightest member of the NGC 7331 Group of galaxies, which is also known as the Deer Lick Group. This small collection - also referred to as the "fleas" - contains four other members, NGC 7335, NGC 7336, NGC 7337 and NGC 7340.
NGC 7331 is visible in large binoculars and small telescopes. From our perspective, it's inclined and appears somewhat like a miniature version of the Andromeda Galaxy (M31). Indeed, the two galaxies are physically very similar in size and shape, although NGC 7331 is about 20x more distant. Of all the Pegasus galaxies visible in backyard scopes, NGC 7331 is the finest.
William Herschel discovered NGC 7331 on September 5, 1784. The galaxy is number 30 in the Caldwell catalogue and is one of the brighter galaxies not included in the Messier catalogue. It's best seen from northern temperate locations during the months of July, August and September.
NGC 7331 is located in a relatively barren region of sky, towards the northern edge of Pegasus and close to the Lacerta constellation boundary. It's positioned a little over 4 degrees north and slightly west of star eta Peg (η Peg - mag. +2.9). This challenging object for 7x50 or 10x50 binocular users requires dark skies and good seeing conditions. It's much easier to catch with small telescopes or larger binoculars, such as 20x80 models. Through an 80mm (3.1-inch) refractor, the galaxy appears as a small oval of gray light. In total, it spans some 10.5 x 4.2 arc minutes of apparent sky, but visually appears only half this size.
With a 200mm (8-inch) reflector, NGC 7331 is easy to spot, appearing elongated with a brighter centre. At 150x magnification through a 400mm (14-inch) scope, it looks much better. The centre appears bright and well defined, with hints of dark dust lanes and mottling beneath the nucleus. Also visible surrounding this superb edge-on spiral are numerous dimmer companions.
Located half a degree southwest of NGC 7331 is a faint group of galaxies, collectively known as Stephan's Quintet. They are named after French astronomer Édouard Jean-Marie Stephan, who discovered them in 1877.
NGC 7331 Data Table
|Object Type||Spiral Galaxy|
|Distance (light-years)||50 Million|
|RA (J2000)||22h 37m 05s|
|DEC (J2000)||+34d 25m 01s|
|Apparent Size (arc mins)||10.5 x 4.2|
|Number of Stars||1 Trillion|
|Notable Feature||Brightest member of the NGC 7331 Group of galaxies|