Galaxy NGC 3631 (Arp 27)

NGC 3631
NGC 3631: Galaxy in Ursa Major; 500 mm Cassegrain 3625 mm f/7.2; SBIG STL11K; 280-120-120-120 min LRGB; Berner Oberland; © 2015 Radek Chromik [32]


This galaxy was discovered on 14 April 1789 by the famous German-British astronomer William Herschel using his selfmade reflecting telescope of 20 foot focal length (aperture 18.7 inch) in Slough near Windsor in Great Britain. He cataloged it as «bright nebula» (class I) with the designation I 226. He noted: «considerably bright, round, small bright resolvable nucleus and very faint chevelure, 4' diameter.» [465] His son John listed it as h 858 (GC 2379) and noted in his catalog of 1833: «pretty bright, large, round, suddenly much brighter in the middle, 2' diameter.» [466] In his catalogue of 1864 John Herschel describes it as «pretty bright, large, round, suddenly very brighter in the middle, barely resolvable nucleus.» [467] John L. E. Dreyer listed this galaxy as NGC 3631 in his «New General Catalogue», published in 1888. [313]

Halton Arp divided his «Atlas of Peculiar Galaxies», published in 1966, into groups based on purely morphological criteria. The galaxy here received the designation Arp 27 (APG 27) as a galaxy with «one heavy arm». He also noted: «Note straight arms, absorption tube crossing from inside to outside of S arm.» [199]

NGC 3631
NGC 3631: Image taken with Hubble Space Telescope. © ESA/Hubble & NASA [525]

Physical Properties

NGC 3631 is a grand-design spiral galaxy of type SAc. The inclination angle of the disc is about 17°, so we see it nearly face-on. The two-armed spiral structure seems to be well defined in optical light, but it has a number of irregularities, especially in the outer parts of the disc. The two-armed spiral structure of NGC 3631 has a wave nature. The observed vertical gas motions represent motions in a spiral density wave. The radius of corotation is about 42 arcsec, or 3.2 kpc. There is evidence of two anticyclonic and four cyclonic vortices near corotation in a frame of reference rotating with the spiral pattern. The centres of the anticyclones lie between the observed spiral arms. The cyclones lie close to the observed spirals, but their centres are shifted from the maxima in brightness. [523, 524]

Revised+Historic NGC/IC Version 22/9, © 2022 Dr. Wolfgang Steinicke [277]
Designation NGC 3631
Type Gx (Sc)
Right Ascension (J2000.0) 11h 21m 02.7s
Declination (J2000.0) +53° 10' 11"
Diameter 5 × 3.7 arcmin
Photographic (blue) magnitude 11.0 mag
Visual magnitude 10.4 mag
Surface brightness 13.7 mag·arcmin-2
Position Angle 114°
Redshift (z) 0.003856
Distance derived from z 16.29 Mpc
Metric Distance 21.600 Mpc
Dreyer Description pB, L, R, svmbMrN
Identification, Remarks WH I 226; h 858; GC 2379; UGC 6360; MCG 9-19-47; CGCG 268-21; Arp 27; VV 363; IRAS 11181+5326

Finder Chart

The galaxy NGC 3631 is located in the constellation Ursa Maior. The constellation is circumpolar, but is highest at night from November to July, which is best for observing.

Finder Chart Galaxy NGC 3631 (Arp 27)
Galaxy NGC 3631 (Arp 27) in constellation Ursa Maior. Charts created using SkySafari 6 Pro and STScI Digitized Sky Survey. Limiting magnitudes: Constellation chart ~6.5 mag, DSS2 close-ups ~20 mag. [149, 160]

Objects Within a Radius of 15°


  • [32] Astrofotografie by Radek, Bernie and Dragan;
  • [149] SkySafari 6 Pro, Simulation Curriculum;
  • [160] The STScI Digitized Sky Survey;
  • [199] «Atlas Of Peculiar Galaxies», Halton Arp, 1966; Astrophysical Journal Supplement, vol. 14, p.1 (1966); DOI:10.1086/190147; Bibcode:1966ApJS...14....1A;
  • [277] «Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; (2021-02-17)
  • [313] «A New General Catalogue of Nebulae and Clusters of Stars, being the Catalogue of the late Sir John F.W. Herschel, Bart., revised, corrected, and enlarged» Dreyer, J. L. E. (1888); Memoirs of the Royal Astronomical Society. 49: 1–237; Bibcode:1888MmRAS..49....1D
  • [465] «Catalogue of 500 new nebulae, nebulous stars, planetary nebula:, and clusters of stars; with remarks on the construction of the heavens» William Herschel, Philosophical Transactions of the Royal Society of London, 1 January 1802; DOI:10.1098/rstl.1802.0021
  • [466] «Observations of nebulæ and clusters of stars, made at Slough, with a twenty-feet reflector, between the years 1825 and 1833» John Frederick William Herschel, Philosophical Transactions of the Royal Society of London, 1 January 1833, Pages: 359-505; DOI:10.1098/rstl.1833.0021
  • [467] «Catalogue of nebulae and clusters of stars» John Frederick William Herschel, Philosophical Transactions of the Royal Society of London, 1 January 1864; DOI:10.1098/rstl.1864.0001;
  • [523] «Vertical motions in the gaseous disk of the spiral galaxy NGC 3631» Fridman, A. M.; Koruzhii, O. V.; Zasov, A. V.; Sil'chenko, O. K.; Moiseev, A. V.; Burlak, A. N.; Afanas'ev, V. L.; Dodonov, S. N.; Knapen, J.; Astronomy Letters, Volume 24, Issue 6, November 1998, pp.764-773; Pis'ma v Astronomicheskii Zhurnal, Vol. 24, p. 883; Bibcode:1998AstL...24..764F
  • [524] «Gas motions in the plane of the spiral galaxy NGC 3631» A. M. Fridman, O. V. Khoruzhii, E. V. Polyachenko, A. V. Zasov, O. K. Sil'Chenko, A. V. Moiseev, A. N. Burlak, V. L. Afanasiev, S. N. Dodonov, J. H. Knapen; Monthly Notices of the Royal Astronomical Society, Volume 323, Issue 3, May 2001, Pages 651–662; DOI:10.1046/j.1365-8711.2001.04218.x
  • [525] Hubble Looks at a Face-On Grand Spiral; (2022-07-10)