Robert's Quartet

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Robert's Quartet
Observation data (Epoch J2000)
Constellation(s) Phoenix
Right ascension 0h 21m 23.075s
Declination −48° 37.75′ 39.5″
Brightest member NGC 92
Number of galaxies 4
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 in the process of colliding and merging.[citation needed] Its members are NGC 87, NGC 88, NGC 89 and NGC 92, discovered by John Herschel on the 30 September 1834.[1]

The quartet is one of the best examples of compact galaxy groups, because such groups contain four to eight galaxies in a very small region.[according to whom?] They are excellent laboratories for the study of galactic interactions and their effects, in particular on the formation of stars. The quartet has a total visual magnitude of almost 13.[citation needed] The brightest member of the group is NGC 92, having the blue magnitude of 13.8.[2] On the sky, the four galaxies are all within a circle of radius of 1.6 arcmin, corresponding to about 75,000 light-years.[citation needed] It was named by Halton Arp and Barry F. Madore, who compiled A Catalogue of Southern Peculiar Galaxies and Associations in 1987.[according to whom?]


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.


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