|Observation data (J2000 epoch)|
|Right ascension||22h 37m 04.1s|
|Declination||+34° 24′ 56″|
|Redshift||816 ± 1 km/s|
|Distance||40 ± 3 e6ly (12.2 ± 1.0 Mpc)|
|Apparent dimensions (V)||10′.5 × 3′.7|
|Apparent magnitude (V)||+10.4|
|UGC 12113, PGC 69327, Caldwell 30|
NGC 7331 (also known as Caldwell 30) is a spiral galaxy about 40 million light-years (12 Mpc) away in the constellation Pegasus. It was discovered by William Herschel in 1784. NGC 7331 is the brightest member of the NGC 7331 Group of galaxies.
The galaxy is similar in size and structure to the galaxy we inhabit, and is often referred to as "the Milky Way's twin", although recent discoveries regarding the structure of the Milky Way may call this similarity into doubt.
In spiral galaxies the central bulge typically co-rotates with the disk but the bulge in the galaxy NGC 7331 is rotating in the opposite direction to the rest of the disk. The current bulge may have formed from infalling material, however if it has been there since the formation of the galaxy then it would be difficult to explain how such a situation arose.
SN 1959D, a Type IIL supernova, is the only supernova that has been identified within NGC 7331. The supernova was discovered by Milton Humason and H. S. Gates in a survey at Palomar Observatory.
Possible 2014 Supernova 
- M94 – another galaxy with a prominent starburst ring
- NGC 1512 – another galaxy with a prominent starburst ring
- "NASA/IPAC Extragalactic Database". Results for NGC 7331. Retrieved 2006-11-10.
- Jensen, Joseph B.; Tonry, John L.; Barris, Brian J.; Thompson, Rodger I.; et al. (February 2003). "Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations". Astrophysical Journal 583 (2): 712–726. arXiv:astro-ph/0210129. Bibcode:2003ApJ...583..712J. doi:10.1086/345430.
- The NGC/IC Project : NGC Discoverers List by Bob Erdmann.
- "Seeing Double: Spitzer Captures Our Galaxy's Twin". Spitzer Space Telescope Newsroom. Spitzer Science Center. 2004-06-28. Archived from the original on May 17, 2007. Retrieved 2008-04-24.
- "The Milky Way Has Only Two Spiral Arms". 2008-06-03. Retrieved 2008-06-04.
- A Counter-rotating Bulge in the Sb Galaxy NGC 7331 , F. Prada, C. Gutierrez, R.F. Peletier, C.D. McKeith, THE ASTROPHYSICAL JOURNAL, 463 :L9–L12, 1996 May 20
- "NASA/IPAC Extragalactic Database". Results for SN 1959D. Retrieved 2006-11-10.
- M. L. Humason; H. S. Gates (1960). "The 1959 Palomar Supernova Search". Publications of the Astronomical Society of the Pacific 72: 208–209. Bibcode:1960PASP...72..208H. doi:10.1086/127513.
- Calar Alto Observatory – NGC 7331
- APOD (2004-07-01) – "A Galaxy So Inclined"
- SST – "Morphology of Our Galaxy's 'Twin'"
- NGC 7331 at the astro-photography site of Mr. T. Yoshida
- NGC7331 at W. Kloehr Astrophotography
- NGC 7331 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images