Messier 91

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Messier 91
Messier 91 (M91).jpg
Spiral Galaxy M91
Observation data (J2000 epoch)
ConstellationComa Berenices
Right ascension 12h 35m 26.4s[1]
Declination+14° 29′ 47″[1]
Redshift486 ± 4 km/s[1]
Distance63 ± 16 Mly (19 ± 5 Mpc)[2]
Apparent magnitude (V)11.0[1]
Apparent size (V)5′.4 × 4′.3[1]
Other designations
NGC 4548,[1] UGC 7753,[1] PGC 41934[1]

Messier 91 (also known as NGC 4548 or M91)[3][4] is a barred spiral galaxy located in the Coma Berenices constellation and is part of the Virgo Cluster of galaxies. M91 is about 63 million light-years away from the earth. It was the last of a group of eight nebulae discovered by Charles Messier in 1781.

Originally M91 was a missing Messier object in the catalogue as the result of a bookkeeping mistake by Messier. It was not until 1969 that amateur astronomer William C. Williams[3] realized that M91 was NGC 4548,[4] which was documented by William Herschel in 1784 (according to other sources, however, the nearby spiral galaxy NGC 4571 was also considered as a candidate for Messier 91 by him.[4])

Messier 91 (M91)

Observation history[edit]

Messier 91 was discovered on the night of March 18, 1781, Charles Messier described it as Nebula without stars, fainter than M90. Messier mistakenly logged its position from Messier 58,[4][5] where in fact it should have been Messier 89. William Herschel observed the same galaxy on April 8, 1784.

In 1969 Williams solved the missing Messier object by measuring its right ascension and declination relative to those of the nearby galaxy M89 (there are no suitable reference stars in the vicinity). Williams applied the observed differences of M91 with M58, a 9th-magnitude galaxy which Messier recorded in 1778. The calculation reproduces the Messier position[3] to 0.1' in right ascension and 1' in declination.


M91 map

The inclusion of Messier 91 in the Virgo Cluster of Galaxies was confirmed in 1997 by a calculation of its distance as 52 +/- 6 million light years from observing Cepheid variables.[4]

M91's bar is very conspicuous where it lies at an angle of 65/245 degrees when being measured from the North direction to the East.[4]

There is a considerable peculiar velocity toward us through the Virgo cluster of about 700 km/s while the cluster's recession velocity is about 1100 km/s, this gives an observed recessional velocity of only about 400 km/s.[4] Another source gives its RV as 803 km/s.[6]

Messier 91 is also classified as an anemic galaxy -i.e., a spiral galaxy with low star formation and content of gas compared with other galaxies of its type-.[7][8]


  1. ^ a b c d e f g h i "NASA/IPAC Extragalactic Database". Results for NGC 4548. Retrieved 2006-12-13.
  2. ^ J. L. Tonry; A. Dressler; J. P. Blakeslee; E. A. Ajhar; et al. (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distance". Astrophysical Journal. 546 (2): 681–693. arXiv:astro-ph/0011223. Bibcode:2001ApJ...546..681T. doi:10.1086/318301.
  3. ^ a b c William C. Williams Letter, Sky and Telescope, December 1969, p. 376. Accessed 13 April 2011
  4. ^ a b c d e f g Students for the Exploration and Development of Space Messier 91, Accessed online 14 April 2011
  5. ^ "Messier 91". University Today. Retrieved 2010-04-14.
  6. ^ Virgo cluster
  7. ^ Vollmer, B.; Cayatte, V.; Boselli, A.; Balkowski, C.; Duschl, W.J. (1999). "Kinematics of the anemic cluster galaxy NGC 4548. Is stripping still active?". Astronomy and Astrophysics. 349: 411–423. arXiv:astro-ph/9907351. Bibcode:1999A&A...349..411V.
  8. ^ Fumagalli, M.; Krumholz, M.R.; Prochaska, J.X; Gavazzi, G.; Boselli, A. (2009). "Molecular Hydrogen Deficiency in H I-poor Galaxies and its Implications for Star Formation". The Astrophysical Journal. 697 (2): 1811–1821. arXiv:0903.3950. Bibcode:2009ApJ...697.1811F. doi:10.1088/0004-637X/697/2/1811.

External links[edit]

Coordinates: Sky map 12h 35m 26.4s, +14° 29′ 47″