Historical Identification: Per Dreyer, NGC 500 (= GC 290, 3rd Lord Rosse, 1860 RA 01 15 23, NPD 85 20.3) is "very faint, very small, much brighter middle, 11th magnitude star 1 arcmin to northeast".
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 Bindon Stoney.
Physical Information: Based on a recessional velocity of 12315 km/sec, a straightforward calculation indicates that NGC 500 is about 575 million light years away. But 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 545 million light years away when the light by which we see it was emitted, about 560 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 0.8 by 0.6 arcmin, NGC 500 is about 125 thousand light years across.

Historical Identification: Per Dreyer, NGC 501(= GC 284, 3rd Lord Rosse, 1860 RA 01 15 33, NPD 57 17.7) is "very faint, small (E in Birr diagram)".
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: Apparent size 0.5 by 0.5 arcmin?

Historical Identification: Per Dreyer, NGC 502 (= GC 293, d'Arrest, 1860 RA 01 15 36, NPD 81 41.0) is "considerably bright, small, round, brighter middle and nucleus".
Physical Information: Apparent size 1.1 by 1.0 arcmin?

Historical Identification: Per Dreyer, NGC 503 (= GC 5169, d'Arrest, 1860 RA 01 15 37, NPD 57 24.2) is "extremely faint, extremely small, double star 4 arcmin to southwest".
Physical Information: Apparent size 0.9 by 0.7 arcmin?

Historical Identification: Per Dreyer, NGC 504 (= GC 291 = GC 292 = JH 107, d'Arrest, 1860 RA 01 15 37, NPD 57 31.7) is "very faint, small".
Physical Information: Apparent size 1.7 by 0.4 arcmin?

Historical Identification: Per Dreyer, NGC 505 (= GC 5170, Marth #46, 1860 RA 01 15 37, NPD 81 16) is "very faint, very small, stellar".
Physical Information: Apparent size 0.9 by 0.6 arcmin?

Historical Identification: Per Dreyer, NGC 506 (= GC 5171, 4th Lord Rosse, 1860 RA 01 15 47, NPD 57 29.8) is "very faint, very small, southwest of h 108", (JH) 108 being NGC 507.

Historical Identification: Per Dreyer, NGC 507 (= GC 294 = JH 108 = WH III 159, 1860 RA 01 15 49, NPD 57 28.6) is "very faint, pretty large, round, brighter middle, southern of 2", the other being NGC 508.
Physical Information: Apparent size 3.0 by 2.5 arcmin. Recessional velocity 4935 km/sec. Thought to be a group member with NGC 508, but not necessarily a physical pair, as there is no evidence of interaction between the galaxies. Used by the Arp Atlas as an example of a galaxy with concentric rings.

Historical Identification: Per Dreyer, NGC 508 (= GC 295 = JH 109 = WH III 160, 1860 RA 01 15 49, NPD 57 27.0) is "very faint, small, northern of 2".
Physical Information: Apparent size 1.1 by 1.1 arcmin? Recessional velocity 5525 km/sec. Thought to be a group member with NGC 507 (which see for images), but not necessarily a physical pair, as there is no evidence of interaction between the galaxies. Generally treated as part of Arp 229, which is an example of a galaxy with concentric rings, but that description and Arp's comment about the entry apply only to NGC 507, so the term "Arp 229" should also be applied only to the larger galaxy.

Historical Identification: Per Dreyer, NGC 509 (= GC 5172, Marth #47, 1860 RA 01 16 03, NPD 81 18) is "very faint, small, extended".
Physical Information: Apparent size 1.6 by 0.6 arcmin?

Historical Identification: Per Dreyer, NGC 510 (= GC 5173, Schultz (Nova V), 1860 RA 01 16 04, NPD 57 14.1) is "very faint, very small, a little extended".

Historical Identification: Per Dreyer, NGC 511 (= GC 5174, Stephan list VIII (#4), 1860 RA 01 16 08, NPD 79 26.5) is "extremely faint, very small, small (faint) star involved, small star attached".
Physical Information: Apparent size 1.0 by 0.9 arcmin. Contains multiple concentric rings.

Historical Identification: Per Dreyer, NGC 512 (= GC 296 = JH 110, 1860 RA 01 16 08, NPD 56 49.9) is "very faint, very small".
Physical Information: Apparent size 1.6 by 0.4 arcmin?

Historical Identification: Per Dreyer, NGC 513 (= GC 297 = JH 111 = WH III 169, 1860 RA 01 16 34, NPD 56 56.5) is "faint, small, stellar".
Physical Information: Apparent size 0.9 by 0.6 arcmin? A Seyfert galaxy (type Sy 1h).

Historical Identification: Per Dreyer, NGC 514 (= GC 298 = JH 112 = WH II 252, 1860 RA 01 16 36, NPD 77 49.2) is "faint, large, a little extended, very gradually a little brighter middle, double star to east".
Physical Information: Apparent size 3.7 by 3.0 arcmin?

Historical Identification: Per Dreyer, NGC 515 (= GC 299 = JH 113 = WH III 167, 1860 RA 01 16 46, NPD 57 15.5) is "pretty faint, very small, round, northwestern of 2", the other being NGC 517.
Physical Information: Apparent size 1.4 by 1.1 arcmin?

Historical Identification: Per Dreyer, NGC 516 (= GC 300, d'Arrest, 1860 RA 01 16 48, NPD 81 10.1) is "extremely faint, small, very difficult, I 151 forty-one seconds of time to east", (WH) I 151 being NGC 524.
Physical Information: Apparent size 1.4 by 0.5 arcmin?

Historical Identification: Per Dreyer, NGC 517 (= GC 301 = JH 114 = WH III 168, 1860 RA 01 16 52, NPD 57 18.1) is "pretty faint, round, stellar, southeastern of 2", the other being NGC 515.
Physical Information: Apparent size 1.4 by 0.5 arcmin?

Historical Identification: Per Dreyer, NGC 518 (= GC 5175, Marth #48, 1860 RA 01 16 57, NPD 81 25) is "faint, very small, round".
Physical Information: Apparent size 1.6 by 0.6 arcmin?

Historical Identification: Per Dreyer, NGC 519 (Swift list VI (#8), 1860 RA 01 17 14, NPD 92 23.7) is "most extremely faint, very small, round, very difficult".
Physical Information: Apparent size 0.5 by 0.3 arcmin?

Historical Identification: Per Dreyer, NGC 520 (= GC 303 = JH 116 = WH III 253, 1860 RA 01 17 19, NPD 86 56.1) is "faint, considerably large, extended 137°." The position precesses to (2000) RA 01 24 33.2, Dec +03 47 47, only 0.2 arcmin southwest of the nucleus of the northwestern nucleus of the galaxy listed above, the description fits and there is nothing else nearby, so the identification is certain.
Discovery Notes: Per details obtained from Gottlieb's website, in can be inferred that Dreyer's description is primarily based on the earlier observations by William and John Herschel, but Stoney, Parsons and Dreyer (all using the 72" 'Leviathan' built by William Parsons, the 3rd Lord Rosse), sketched and/or noted the fan-like appearance of the southeastern part of the "nebula", and Parsons noted that it had two points of condensation about 3/4 of an arcmin apart (the nuclei of the merging galaxies).
Physical Information: Apparent size 3.4 by 1.7 arcmin? A pair of merging galaxies.
Usage By The Arp Atlas: The Arp Atlas of Peculiar Galaxies used NGC 520 as an example of a disturbed galaxy with interior absorption, with the comment "Note segment in NE direction." However, Arp probably meant "SE", as there is nothing to the northeast of the object.

Historical Identification: Per Dreyer, NGC 521 (= GC 304 = JH 115 = WH II 461, 1860 RA 01 17 21, NPD 89 00.0) is "faint, pretty large, round, gradually brighter middle".
Physical Information: Apparent size 2.7 by 2.4 arcmin?

Historical Identification: Per Dreyer, NGC 522 (= GC 305, d'Arrest, 1860 RA 01 17 23, NPD 80 44.4) is "extremely faint, pretty large, irregular figure, perhaps cluster plus nebula".
Physical Information: Apparent size 2.8 by 0.5 arcmin?

Historical Identification: Per Dreyer, NGC 523 (= GC 306 = WH III 170?, d'Arrest, 1860 RA 01 17 25, NPD 56 42.4) is "a double nebula, very faint, very small, position angle 90°, distance 30 arcsec", the question mark after (WH) III 170 being a suggestion that this might be a duplicate of NGC 537 (which turned out to be correct).
Physical Information: Apparent size 2.5 by 0.7 arcmin? Used by the Arp Atlas as an example of a disturbed galaxy with interior absorption. Probably the result of a collision between two galaxies, its "double" appearance being due to their two nuclei, and most likely destined to merge into a single galaxy.

Historical Identification: Per Dreyer, NGC 524 (= GC 307 = JH 117 = WH I 151, 1860 RA 01 17 27, NPD 81 11.6) is "very bright, pretty large, much brighter middle, 4 small (faint) stars near".
Physical Information: Apparent size 4.2 by 4.0 arcmin.

Historical Identification: Per Dreyer, NGC 525 (= GC 308, d'Arrest, 1860 RA 01 17 32, NPD 81 01.7) is "very faint, very small, 11th or 12th magnitude star 5 seconds of time to west".
Physical Information: Apparent size 1.5 by 0.7 arcmin?

Historical Identification: Per Dreyer, NGC 526 (= GC 309 = JH 2408, 1860 RA 01 17 35, NPD 125 48.1) is "faint, small, a little extended, the preceding (western) of 2", the other being NGC 527.
Physical Information: The description "a little extended" is probably due to NGC 526 consisting of two galaxies, as listed above: 1.2 by 0.6 arcmin wide PGC 5120, and 0.8 by 0.4 arcmin wide PGC 5135. The DSS image suggests and the HST image shows that the galaxies are almost certainly a physically interacting pair.

Historical Identification: Per Dreyer, NGC 527 (= GC 310 = JH 2409, 1860 RA 01 17 38, NPD 125 51.0) is "faint, small, a little extended, brighter middle, the following (eastern) of 2", the other being NGC 526.
Physical Information: Apparent size 1.6 by 0.3 arcmin. Recessional velocity 5800 km/sec. (PGC 5142 is too faint to be considered part of NGC 527, but it is a companion of NGC 527 and sometimes called NGC 527B, so it is discussed immediately below.)

Physical Information: Apparent size 0.6 by 0.2 arcmin?? Recessional velocity 5880 km/sec. A companion of NGC 527, which see for images.

Historical Identification: Per Dreyer, NGC 528 (= GC 5176, d'Arrest, 1860 RA 01 17 41, NPD 57 03.7) is "faint, pretty large, round, a little brighter middle".
Physical Information: Apparent size 1.2 by 0.8 arcmin?

Historical Identification: Per Dreyer, NGC 529 (= GC 311 = JH 118, 1860 RA 01 17 46, NPD 56 01.0) is "pretty bright, very small, suddenly brighter middle, western of 2", the other being NGC 536.
Physical Information: Apparent size 2.4 by 2.1 arcmin. A member of Hickson Compact Group 10, consisting of NGC 529, 531, 536 (which see for additional images) and 542.

Historical Identification: Per Dreyer, NGC 530 (Swift list VI (#9), 1860 RA 01 17 49, NPD 92 19.4) is "extremely faint, small, much extended, faint star to southeast". The second Index Catalog lists a corrected 1860 RA (per Howe) of 01 17 34 and notes "Is = IC 106" (which see for a discussion of the double listing).
Physical Information: Part of galaxy cluster Abell 194. Based on a recessional velocity of 5005 km/sec, NGC 530 is about 235 million light years away. Given that and its apparent size of 1.5 by 0.4 arcmin, it is about 100 thousand light years across.

Historical Identification: Per Dreyer, NGC 531 (= GC 312, 3rd Lord Rosse, 1860 RA 01 17 55, NPD 55 58.4) is "faint, small, round".
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: Apparent size 1.8 by 0.5 arcmin. A member of Hickson Compact Group 10, consisting of NGC 531, 529, 536 (which see for additional images) and 542.

Historical Identification: Per Dreyer, NGC 532 (= GC 313 = GC 314 = JH 119 = WH III 556, 1860 RA 01 17 59, NPD 81 28.0) is "very faint, pretty large, extended 30°, brighter middle".
Physical Information: Apparent size 3.1 by 1.0 arcmin?

Historical Identification: Per Dreyer, NGC 533 (= GC 315 = JH 121 = WH II 462, 1860 RA 01 18 19, NPD 88 58.2) is "pretty bright, pretty large, round, gradually brighter middle".
Physical Information: Apparent size 3.8 by 2.3 arcmin?

Historical Identification: Per Dreyer, NGC 534 (= GC 316 = JH 2410, 1860 RA 01 18 23, NPD 128 52.2) is "most extremely faint, small, round, very gradually brighter middle, 1st of 4", the others being NGC 544, 546 and 549.
Physical Information: Apparent size 1.0 by 0.9 arcmin?

Historical Identification: Per Dreyer, NGC 535 (= GC 5177, d'Arrest, 1860 RA 01 18 23, NPD 92 07.8) is "very faint, very small, 1st of 3"; which the other 2 of 3 are is not specified by Dreyer, but based on their position and their discovery by d'Arrest, they are probably NGC 541 and 543.
Physical Information: Apparent size 1.0 by 0.3 arcmin.

Historical Identification: Per Dreyer, NGC 536 (= GC 317 = GC 325 = JH 120 = WH III 171, 1860 RA 01 18 27, NPD 56 01.4) is "pretty bright, pretty large, gradually brighter middle, eastern of 2", the other being NGC 529.
Physical Information: Apparent size 3.3 by 1.2 arcmin. A member of Hickson Compact Group 10, consisting of NGC 536, 529, 531 and 542.

Historical Identification: Per Dreyer, NGC 537 (= GC 319 = WH III 170, 1860 RA 01 18 27, NPD 56 39.1) is "stellar (perhaps = GC 306?)", GC 306 being NGC 523, so Dreyer's suggestion of the duplicate entry turned out to be correct.
Physical Information: Given the duplicate entry, see NGC 523 for anything else.

Historical Identification: Per Dreyer, NGC 538 (Swift list VI (#10), 1860 RA 01 18 29, NPD 92 16.4) is "extremely faint, small, much extended, faint star to north".
Physical Information: Apparent size 1.3 by 0.6 arcmin.

Historical Identification: Per Dreyer, NGC 539 (Leavenworth list I (#28), 1860 RA 01 18 30, NPD 108 55.4) is "very faint, very small, round".
Physical Information: Apparent size 1.6 by 1.3 arcmin?

Historical Identification: Per Dreyer, NGC 540 (Leavenworth list I (#29), 1860 RA 01 18 30, NPD 110 41.4) is "very faint, very small, round, suddenly brighter middle and nucleus".
Physical Information: Apparent size 0.9 by 0.4 arcmin?

Historical Identification: Per Dreyer, NGC 541 (= GC 5178, d'Arrest, 1860 RA 01 18 36, NPD 92 06.1) is "faint, small, round, brighter middle". The position precesses to (2000) RA 01 25 44.3, Dec -01 22 18
Physical Information: Apparent size 1.9 by 1.4 arcmin (from image below) Used by the Arp Atlas of Peculiar Galaxies as an example of an elliptical or lenticular galaxy with nearby fragments.

Historical Identification: Per Dreyer, NGC 542 (= GC 318, 3rd Lord Rosse, 1860 RA 01 18 38, NPD 56 03.3) is "extremely faint, difficult".
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: Apparent size 1.0 by 0.2 arcmin? A member of Hickson Compact Group 10, consisting of NGC 542, 529, 531 and 536 (which see for more images).

Historical Identification: Per Dreyer, NGC 543 (= GC 5179, d'Arrest, 1860 RA 01 18 42, NPD 92 01.8) is "extremely faint, extremely small".
Physical Information: Apparent size 0.6 by 0.3 arcmin?

Historical Identification: Per Dreyer, NGC 544 (= GC 320 = JH 2411, 1860 RA 01 18 51, NPD 128 49.0) is "most extremely faint, small, round, very gradually brighter middle, 2nd of 4", the others being NGC 534, 546 and 549.
Physical Information: Apparent size 1.5 by 1.1 arcmin?

Historical Identification: Per Dreyer, NGC 545 (= GC 322 = WH II 448, 1860 RA 01 18 51, NPD 92 04.0) is "stellar, preceding (western) of double nebula", the other being NGC 547. The position precesses to (2000) RA 01 25 59.3, Dec -01 20 13,
Physical Information: Vr 5340 km/sec. 54.7 to 91.6 Mpc. Apparent size 3.65 by 1.55 arcmin (from images below). A double system with NGC 547, with which it is used by the Arp Atlas as an example of "Unclassified Objects" (most of which are galaxy pairs). Misidentified by MCG as NGC 547A.

Historical Identification: Per Dreyer, NGC 546 (= GC 321 = JH 2412, 1860 RA 01 18 52, NPD 128 47.3) is "most extremely faint, small, round, very gradually better middle, 3rd of 4", the others being NGC 534, 544 and 549.
Physical Information: Apparent size 1.4 by 0.5 arcmin?

Historical Identification: Per Dreyer, NGC 547 (= GC 323 = WH II 449, 1860 RA 01 18 53, NPD 92 04.3) is "stellar, following (eastern) of double nebula", the other being NGC 545. The position precesses to (2000) RA 01 26 01.3, Dec -01 20 31,
Physical Information: Vr 5470 km/sec. 44.4 to 84.7 Mpc. Apparent size 1.6 by 1.35 arcmin. A double system with NGC 545 (which see for images), with which it is used by the Arp Atlas as an example of "Unclassified Objects" (most of which are galaxy pairs). Per NED, misidentified as NGC 547B by MCG.

Historical Identification: Per Dreyer, NGC 548 (Searle (25, HN 33), 1860 RA 01 18 53, NPD 91 57.3) is "extremely faint, extremely small".
Physical Information: Apparent size 0.8 by 0.5 arcmin?

Historical Identification: Per Dreyer, NGC 549 (= GC 324 = JH 2413, 1860 RA 01 19 07, NPD 128 44.7) is "most extremely faint, small, round, very gradually brighter middle, 4th of 4", the others being NGC 534, 544 and 546. (Need to add discussion of how the correct object was identified.)
Historical Misidentification: The SGC (Southern Galaxy Catalog) misidentified NGC 549 as PGC 5278, and though that mistake has been corrected in many places, it still exists in a number of others (Example: A Wikisky search for NGC 549 shows PGC 5278, so to see the correct NGC 549 you have to enter the coordinates or PGC designation for PGC 5243). As a result of that error, PGC 5278 is discussed in the next entry.
Physical Information: Apparent size 0.5 by 0.4 arcmin?

Historical Misidentification: As will be noted in the discussion of NGC 549, PGC 5278 was misidentified as that object in the SGC (Southern Galaxy Catalog). Though not yet posted there, Herschel's position was poor, but his description of the nebula and the relative position of its neighboring galaxies makes it absolutely certain that NGC 549 is PGC 5243, and not PGC 5278; but the mistaken identification is still found in a number of places, hence this warning about the mistake.
Physical Information: