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IC 5350 - 5386 ← NGC Objects: NGC 1 - 49 → NGC 50 - 99
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Page last updated Aug 12, 2017

NGC 21 (=
NGC 29 = PGC 767)
Discovered (Nov 26, 1790) by William Herschel (and later listed as NGC 29)
Also observed (Nov 11, 1827) by John Herschel (and later listed as NGC 29)
Recorded (Sep 20, 1885) by Lewis Swift (and later listed as NGC 21)
A magnitude 12.7 spiral galaxy (type SAB(s)bc?) in Andromeda (RA 00 10 46.9, Dec +33 21 10)
Historical Identification: Per Dreyer, NGC 21 (Swift list II (#5), 1860 RA 00 02 25, NPD 57 34.1) is "extremely faint, small, a little extended". Swift's position precesses to RA 00 09 38.5, Dec +33 12 39, but there is nothing there. However, as noted in the discussion of NGC 6, this is one of several galaxies discovered by Swift on the same night which mostly share an average error of 70 seconds of time too far west and 8' 12" too far south. Applying that correction, Swift's position for his II-5 precesses to RA 00 10 48.9, Dec +33 20 53, on the southeastern rim of the galaxy listed above and the description fits, so the identification is considered certain. The duplicate entry is due to the fact that with such a large error in Swift's position, there was no way for Dreyer to realize that it was an observation of a previously discovered nebula.
Note About Frequent Confusion With NGC 19: NGC 21 is almost due north of NGC 19, and Swift's incorrect declination for NGC 21 lies about halfway between them. Unfortunately, several catalogs rapidly put together in the 1970's misidentified the southern galaxy as NGC 21. It was only fairly recently that studies of the original observations of NGC objects showed that the southern galaxy was actually NGC 19. So although almost all modern references have corrected the error, a warning about a possible misidentification of NGC 19 as NGC 21 is still appropriate.
Physical Information: Based on a recessional velocity of 4770 km/sec (and H0 = 70 km/sec/Mpc), NGC 21 is about 220 to 225 million light years away, in good agreement with redshift-independent distance estimates of 200 to 270 million light years. Given that and its apparent size of about 1.65 by 0.75 arcmin (from the images below, counting the faint extension of the eastern spiral arm), it is about 105 to 110 thousand light years across.
SDSS image of region near spiral galaxy NGC 21
Above, a 12 arcmin wide SDSS image centered on NGC 21
Below, a 1.6 arcmin wide SDSS image of the galaxy
SDSS image of spiral galaxy NGC 21

NGC 29 (=
NGC 21 = PGC 767)
Discovered (Nov 26, 1790) by William Herschel (and later listed as NGC 29)
Also observed (Nov 11, 1827) by John Herschel (and later listed as NGC 29)
Recorded (Sep 20, 1885) by Lewis Swift (and later listed as NGC 21)
A magnitude 12.7 spiral galaxy (type SAB(s)bc?) in Andromeda (RA 00 10 46.9, Dec +33 21 10)
Historical Identification: Per Dreyer, NGC 29 (= GC 14 = JH 6 = WH II 853, 1860 RA 00 03 32, NPD 57 25.6) is "pretty bright, pretty large, extended 0". The position precesses to RA 00 10 46.1, Dec +33 21 09, within 0.2 arcmin of the center of the galaxy listed above and well within its outline.
Physical Information: The galaxy is sometimes called NGC 29, but since the lower NGC number is usually used for duplicate entries, see NGC 21 for anything else.

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IC 5350 - 5386 ← NGC Objects: NGC 1 - 49 → NGC 50 - 99