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Форум » Досуг » Космос » NGC 27
NGC 27
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NGC 27 (другие обозначения — UGC 96, MCG 5-1-44, ZWG 499.63, KCPG 3B, IRAS00079+2843, PGC 742) — спиральная галактика (Sb) в созвездии Андромеда.

Галактика была открыта американским астрономом Льюисом Свифтом 3 августа 1884.
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NGC 27 (= PGC 742)
Discovered (Aug 3, 1884) by Lewis Swift
A magnitude 13.5 spiral galaxy (type Sbc?) in Andromeda (RA 00 10 32.8, Dec +28 59 46)
Historical Identification: Per Dreyer, NGC 27 (Swift list I (#1), 1860 RA 00 03 15, NPD 61 47.3) is "extremely faint, very small, extended, bright star near". The position precesses to RA 00 10 28.3, Dec +28 59 27, only an arcmin southwest of the galaxy listed above, and less than half an arcmin from its apparent companion, PGC 731. The bright star directly below PGC 742 makes the identification of NGC 27 with one of the two galaxies certain, and although Swift's position is closer to PGC 731 than PGC 742, the two magnitude difference in their brightness makes it certain that what Swift observed was the brighter galaxy.
Observational Note: Although the modern photographs below make it seem like Swift could just as easily have seen both galaxies as only the brighter one, the fact that galaxies are much fainter as visual objects than stars makes it extremely unlikely that he could have seen the fainter one. To show how difficult (or impossible) it would have been for Swift to see PGC 731, the last image for this entry is a simulation of the 33 arcmin field of view used by him, more nearly as seen visually than in a photograph. But even though Swift almost certainly could not see the fainter galaxy, since it is so obvious in modern photographs it is discussed immediately following this entry.
Physical Information: Based on a recessional velocity of 7035 km/sec, NGC 27 is about 325 million light years away, in good agreement with redshift-independent distance estimates of 270 to 320 million light years. 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 less than 320 million light years away at the time the light by which we see it was emitted, more than 320 million years ago (the slight 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 1.15 by 0.5 arcmin, it is about 105 thousand light years across. (NED also lists a second recessional velocity measurement of 7850 km/sec, but that is undoubtedly a misassigned value for PGC 731, and a good example of why it is necessary to be careful in identifying galaxies by one designation or another.) Although NGC 27 and PGC 731 appear to be close to each other, the fainter galaxy is probably 40 million light years further away, making them most likely merely optical companions.
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