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. Its members are NGC 87, NGC 88, NGC 89 and NGC 92, discovered by John Herschel in the 1830s. NGC 101 is also a loosely related member.

The quartet is one of the finest examples of compact groups of galaxies. 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. The quartet has a total visual magnitude of almost 13. The brightest member of the group has a magnitude of about 14. On the sky, the four galaxies are all within a circle of radius of 1.6 arcmin, corresponding to about 75,000 light-years. It was named by Halton Arp and Barry F. Madore, who compiled A Catalogue of Southern Peculiar Galaxies and Associations in 1987.


Members of Robert's Quartet
Name Type Distance from Sun
(million ly)
NGC 87 IBm pec. 155 +14.5
NGC 88 SB(rs)a pec. 156 +15.21
NGC 89 SB0(s)a pec. 149 +14.57
NGC 92 SAa pec. 146 +14.29
NGC 101 Sc 154 +13.46
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″