Robert's Quartet

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Robert's Quartet
Observation data (Epoch J2000)
Right ascension 0h 21m 23.075s
Declination−48° 37.75′ 39.5″
Brightest memberNGC 92
Number of galaxies4
Other designations
AM 0018-485
See also: Galaxy groups, Galaxy clusters, List of galaxy clusters

Robert's Quartet is a compact galaxy group approximately 160 million light-years away in the constellation Phoenix. It is a family of four very different galaxies whose proximity to each other has caused the creation of about 200 star-forming regions and pulled out a stream of gas and dust 100,000 light years long.[1] Its members are NGC 87, NGC 88, NGC 89 and NGC 92, discovered by John Herschel on the 30 September 1834.[2]

The quartet is one of the best examples of compact galaxy groups.[1] Because such groups contain four to eight galaxies in a very small region they are excellent laboratories for the study of galactic interactions and their effects, in particular on the formation of stars.[3] The quartet has a total visual magnitude of almost 13.[3] The brightest member of the group is NGC 92, having the blue magnitude of 13.8.[4] On the sky, the four galaxies are all within a circle of radius of 1.6 arcmin, corresponding to about 75,000 light-years.[3] It was named by Halton Arp and Barry F. Madore, who compiled A Catalogue of Southern Peculiar Galaxies and Associations in 1987.[3] Arp and Madore named Robert's Quartet after Robert Freedman who generated many of the updated positions of galaxies in the catalogue.[3]


Members of Robert's Quartet
Name Type Distance from Sun
(million ly)
NGC 87 IBm pec. ~160 +14.5
NGC 88 SB(rs)a pec. ~160 +15.21
NGC 89 SB0(s)a pec. ~160 +14.57
NGC 92 SAa pec. ~160 +14.29
The largest member of the galaxy group known as Roberts Quartet is NGC 92, a spiral Sa galaxy with an unusual appearance.


  1. ^ a b Darling, David. "Robert's Quartet". David Darling. Retrieved 21 January 2019.
  2. ^ Herschel, John Frederick William (1847). Results of astronomical observations made during the years 1834, 5, 6, 7, 8, at the Cape of Good Hope: being the completion of a telescopic survey of the whole surface of the visible heavens, commenced in 1825. 1. London, United Kingdom: Smith, Elder and Co. p. 51.
  3. ^ a b c d e "Cosmic Portrait of a Perturbed Family". European Southern Observatory. Retrieved 21 January 2019.
  4. ^ "NGC 92". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-09-24.

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Coordinates: Sky map 00h 21m 23.075s, −48° 37.75′ 39.5″