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Форум » Досуг » Космос » NGC 31
NGC 31
ingvarr
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NGC 31 (другие обозначения — ESO 149-20, AM 0007-571, PGC 751) — спиральная галактика (Sc) в созвездии Феникс.

Этот объект входит в число перечисленных в оригинальной редакции «Нового общего каталога».

Галактика была открыта английским астрономом Джоном Гершелем 28 октября 1834.
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NGC 31 (= PGC 751)
Discovered (Oct 28, 1834) by John Herschel
A magnitude 13.9 spiral galaxy (type SAB(rs)cd?) in Phoenix (RA 00 10 38.4, Dec -56 59 11)
Historical Identification: Per Dreyer, NGC 31 (= GC 15 = JH 2311, 1860 RA 00 03 39, NPD 147 46.4) is "most extremely faint, small, round, following (eastern) of 2", the other being NGC 28. The position precesses to RA 00 10 40.2, Dec -56 59 38, which is, as for NGC 28, southeast of the center of the galaxy listed above (in this case, about 0.6 arcmin), but still near the outline of the galaxy. It definitely "follows" NGC 28, which lies just to its west, so the identification is certain. However, as noted by Corwin, at one time some catalogs misidentified NGC 28 as NGC 31, and vice-versa; so the reader may still see their PGC designations reversed in some places. (It is interesting to note the difference between interpretations based on modern photographic images, and the direct observational techniques of the 19th century. Nowadays the ability to photograph the faint outer regions of the galaxy makes NGC 31 appear much larger than and just as bright as NGC 28; but Herschel saw only the bright core of NGC 31, making it appear to be substantially fainter.)
Physical Information: Based on a recessional velocity of 9600 km/sec, a straightforward calculation indicates that NGC 31 is about 445 million light years away. However, for objects at such distances we should take into account the expansion of the Universe during the time it took their light to reach us. Doing that shows that the galaxy was about 430 million light years away at the time the light by which we see it was emitted, a little over 435 million years ago (the difference between the two numbers being due to the expansion of the intervening space during the light-travel time). Given that and its apparent size of 1.2 by 0.6 arcmin, it is about 150 thousand light years across. Like nearby NGC 28, it may be an unlisted member of Abell 2731, and since the two galaxies have nearly identical recessional velocities, regardless of their association with the cluster (or not), they may be physical companions.

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