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Page last updated Aug 12, 2017

NGC 20 (= PGC 679 =
NGC 6)
Discovered (Sep 18, 1857) by R. J. Mitchell (and later listed as NGC 20)
Also observed (Oct 16, 1866) by Herman Schultz (and later listed as NGC 20)
Recorded (Sep 20, 1885) by Lewis Swift (and later listed as NGC 6)
A magnitude 13.1 lenticular galaxy (type E/S0?) in Andromeda (RA 00 09 32.7, Dec +33 18 32)
Historical Identification: Per Dreyer, NGC 20 (= GC 6 = GC 5086, 3rd Lord Rosse, Schultz (Nova II), 1860 RA 00 02 21, NPD 57 28.2) is "faint, 10th magnitude star attached". The position precesses to RA 00 09 34.4, Dec +33 18 34, only 2 seconds of time east of the center of the galaxy listed above, between the galaxy and the 10th magnitude star that lies almost in front of it, so the identification is certain.
Note About The Duplicate Entry With NGC 6: As noted in the discussion of NGC 6, Swift had a large positional error for several objects observed by him on Sep 20, 1885, so Dreyer had no reason to believe that Swift's and Mitchell's objects were were in any way related, leading to duplicate entries for what turned out to be the same object. In such a case, the lower NGC number is usually given preference; but since the identification of NGC 6 as a duplicate entry for NGC 20 was long-delayed, PGC 679 is referred to as NGC 20 about as often as NGC 6.
Discovery Notes: Although Dreyer credits the discovery to William Parsons, 3rd Earl of Rosse, he notes that many of Rosse's nebular discoveries were actually made by one of his assistants, in this case R. J. Mitchell.
Physical Information: Based on a recessional velocity of 4970 km/sec (and H0 = 70 km/sec/Mpc), NGC 20 is about 230 to 235 million light years away. Given that and its apparent size of about 1.9 by 1.5 arcmin (from the images below), it is about 125 to 130 thousand light years across.
SDSS image of region near lenticular galaxy NGC 20
Above, a 12 arcmin wide SDSS image centered on NGC 20
Below, a 2.4 arcmin wide SDSS image of the galaxy
SDSS image of lenticular galaxy NGC 20
Below, a 12 arcmin wide SDSS image centered on NGC 20;
also shown are PGC 212477, 2026460 and 2027085
SDSS image of region near lenticular galaxy NGC 20, also showing numerous PGC objects
NGC 6 (probably =
NGC 20 = PGC 679)
Discovered (Sep 18, 1857) by R. J. Mitchell (and later listed as NGC 20)
Also observed (Oct 16, 1866) by Herman Schultz (and later listed as NGC 20)
Recorded (Sep 20, 1885) by Lewis Swift (and later listed as NGC 6)
A magnitude 13.1 lenticular galaxy (type E/S0?) in Andromeda (RA 00 09 32.7, Dec +33 18 32)
Historical Identification: Per Dreyer, NGC 6 (Swift list II (#3), 1860 RA 00 01 05, NPD 58 15.6) is "extremely faint, very small, considerably extended". The position precesses to RA 00 08 17.7, Dec +32 31 10, but there is nothing there. However (per Corwin), on the night in question Swift discovered four other nebulae (NGC 19, 21, 7831 and 7836) with an average measurement error of 70 seconds of time too far west and 8' 8" too far south, presumably due to improperly setting the setting circles he used to make his measurements at the start of the evening (another galaxy found later that night had a completely different error in position, suggesting that Swift finally realized that the setting circles were "off" and "re-zeroed" them). Applying a corresponding correction to Swift's original measurement yields a position of RA 00 09 28.3, Dec +32 39 17, only a few seconds west of Mitchell's essentially perfect position for NGC 20, but still 39 arcmin too far south of that galaxy. Since Swift used setting circles to measure positions and often misread them, that could be explained by assuming he made an error of 40 arcmin in reading the declination circle. Corwin says it appears that was probably the case here, because Swift's paper states that "one of 5 stars which point to it is pretty near", and there is such a line of stars directly east of NGC 20, the nearest of which is so close to the galaxy that it perfectly fits Mitchell's description of the nebula as having an "attached" star; so he feels that the equality of the two entries is reasonably certain, and I can't help but agree, as indicated by the heading for this entry.
Physical Information: Duplicate entries are usually listed under the lowest NGC number, so some references refer to this object as NGC 6; but because of the uncertainty involved in identifying it as PGC 679, the galaxy is more often referred to as NGC 20, so see that entry for anything else.
SDSS image centered on Dreyer's position for NGC 6
Above, a 12 arcmin wide SDSS image centered on Dreyer's position for NGC 6
Below, a 12 arcmin wide SDSS image centered on NGC 20, which is almost certainly NGC 6
SDSS image of region near lenticular galaxy NGC 20, which is almost certainly NGC 6

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