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The New General Catalogue (NGC) by J.L.E. Dreyer, published in 1886, is a
compilation of 7,840 deep-sky objects previously recorded by a number of
visual observers, principally William and his son, John Herschel. Since
the publication of this catalogue, the literature of astronomy has used the
NGC numbering scheme as the principal designation for those galaxies,
clusters and nebulae that Dreyer included. However, many of the objects
were not independently checked and verified, so a number of non-existent
objects, duplicate entries and positional errors were recorded. Dreyer
caught some of the mistakes and published the correct information as
appendices to his two Index Catalogues (IC I and IC II) which followed in
1895 and 1908.
Photographic surveys such as the Palomar Observatory Sky Survey (POSS) compiled from 1950-1956 under the sponsorship of the National Geographic Society, using the 48" Palomar Schmidt camera, provided a more reliable check on the accuracy of the NGC entries. The Revised New General Catalogue (RNGC) by Jack Sulentic and William Tifft in 1973 used the POSS to photographically identify the NGC objects, provide accurate coordinates (epoch 1975) and give modern descriptions based on their photographic appearance. In cases where no identifiable object was located within a 5' radius of the originally published NGC coordinates, the object was labeled as "nonexistent" and placed in their Class 7. Unfortunately, the RNGC and other modern catalogues have sometimes been misled in their identifications by previous NGC errors in description and position and in a number of cases introduced new errors. In these cases, it is necessary to refer to the original sources to attempt to untangle the correct identities.
The following is a list of error and misidentifications in the RNGC which I have either gleaned from other articles or have uncovered in my own investigation. If you have comments on this list or if there are additions errors in the RNGC you are aware of, I would like to hear from you. Perhaps a definitive NGC will one day be published!
NGC 408: Schultz placed his discovery 8 seconds of RA preceding N410 which corresponds to 1.7 arc minutes west. In this position on the POSS is a 14-15th magnitude star with GSC position 01 10 51.1 +33 09 05 (2000) that almost certainly is Schultz's object. The RNGC has instead chosen for N408 an anonymous galaxy located 3' SSW of N408. Since Schultz placed his "nova" due west of N410 the RNGC identification is very questionable and N408 is a single star. Dorothy Carlson, in her 1939 article on NGC errata, also came to this conclusion although Reinmuth describes this object as a "nebulous *14.". Finally, the RNGC has misinterpreted the NGC description to read "406 F 8S" instead of "410 F 8S".
NGC 512: Discovered by John Herschel (h110). His discovery position is just 23" south of UGC 944. The new description in the RNGC "R, SLDIF, BM, BELCOM2=82N" refers to CGCG 521-017 which is an anonymous companion located 2.5' S of N512. The bright, elongated companion 2' N mentioned in the RNGC description actually refers to N512!
NGC 545, 547, 547A: N545 and N547 were discovered by William Herschel (II 448 and II 449). Herschel described the pair as "Two. Both stellar, within 1' dist. Nebulosities run together." Both objects were given a single position by Herschel. These galaxies are the brightest in Abell 194 and his description is quite accurate as both galaxies are encased in a common envelope. The RNGC incorrectly lists the double galaxy as N547/N547A and reassigns N545 to a 15th magnitude galaxy (M+00-04-140) west of the bright pair. The MCG incorrectly lists the double galaxy as N547a and N547b and also misidentifies identifies N545 as M+00-04-140.
NGC 1627, 1628: The new descriptions in the RNGC are reversed for these two galaxies. The edge-on Sb galaxy to the north at 4h 36.3m -04 45 (1975) is N1628. The Sc system to the south at 4h 36.3 -04 54 is N1627. While the RNGC RA and dec are correct, the "Y" rectangular coordinates are also reversed.
NGC 2288, 2289, 2290, 2291: William Herschel was the first observer of this group and recorded III 897 along with III 898. His description reads "two nebulae. The most n and p; eF and S. The other eF, vS, dist. 4'." These two galaxies were also observed by John Herschel (same orientation and 3 or 4' apart). Assuming both Herschels observed the brightest two galaxies with this orientation, then III 897 = h409 = N2289 and III 898 = h410 = N2290. In the NGC Dreyer incorrectly assigned III 898 = h 410 = N2289 and III 897 = N2290 or III 897 = h409 = N2291.
To further confuse the situation, the identifications of N2288 (discovered by Lord Rosse) and brighter N2289 are reversed in the RNGC. In the MCG, N2289 = M+06-15-010 is also misidentified as N2288 and N2289 = M+06-15-011 is listed as an anonymous galaxy. Malcolm Thomson discusses this group in detail in WSQJ 1/84.
NGC 2830, 2831, 2832: These numbers refer to three galaxies in the core of the rich cluster Abell 779. William Herschel discovered by brightest member which he assigned the number I 113. Due to an error, Dreyer assigned this number to the southwest member of this trio N2830 (actually discovered by Lord Rosse), although the brightest galaxy in the cluster is clearly the northeast galaxy, N2832. Possibly due to this mix-up, RNGC and MCG reverse the identifications of N2830 and N2831(the edge-on galaxy is N2830). The correct identifications are given in UGC, CGCG and RC3. Malcolm Thomson discusses this group in detail in WSQJ 1/78.
NGC 3191, 3192: The first observation of this field was by William Herschel who listed III 704 as "eF, vS, perhaps a patch of S st". The entry for N3191 is attributed to John Herschel's h691 recorded as "F, S, R, bM, 15-20". If this be III 704, there must be a great error in PD on one or other side." In Dreyer's Scientific Papers of William Herschel, he notes "perhaps = h691 [N3191], F, S, R, bM, one obs, which is 8' due S of H's place." As there is only one reasonably bright galaxy in the region, both William and John probably observed the same object. and N3191 = N3192. The RNGC incorrectly identifies N3192 as the extremely faint galaxy M+08-19-017 which is located 1.3' southwest of N3191. Discussed by Malcolm Thompson in WSQJ 4/80 and Betelgeuse 11/1979.
NGC 3745, 3746, 3748, 3750, 3751, 3753, 3754: Copeland's septet is listed as nonexistent in the RNGC due to incorrect coordinates in the NGC. The positions were later corrected by Dreyer in the IC 1 notes. Harold Corwin gives the following corrected data for the RNGC:
NGC 3850, 3889: N3889 was discovered at Birr Castle during observation of N3888 and described on March 13, 1852 as "another F, S, 5' nf." A second observation in 1878 described "Nova, vF, vS, Pos 167.2 deg, Dist 340.5"." This placed the object southeast of N3888 instead of northeast and in compiling the NGC, Dreyer was swayed by the second observation and placed N3889 just 2 seconds of RA following N3888 and 5.6' south. There is no object at the NGC position for N3889 but 3.7' northeast of N3888 is located the faint galaxy M+09-19-191 which was visible in my 17.5" scope and is a reasonable match in position and brightness.
In an attempt to identify N3889, the RNGC assigns it the same coordinates and new description as N3850 which is located 17' WSW of N3888! So, the RNGC position should be changed to 11h 46.6m +56d 09' (1975) and the description to M+09-19-191. This identification mix-up is described in detail by Malcolm Thompson in WSQJ 1/85.
NGC 4565A: While the letter designations found in RNGC are generally anonymous galaxies near brighter galaxies and catalogued in MCG and CGCG, N4565A is just a duplicate entry for N4562. This galaxy was discovered by Tempel and simply placed southwest of N4565 without specific coordinates. This places some ambiguity on the identity of N4562 and this may have lead to the additional catalogue designation.
NGC 4882: Discovered by d'Arrest. The RNGC position is 0.2 minutes of RA preceding N4886 but there is no galaxy near that position . There is a faint star nearby which may be the object RNGC is identifying as N4882. d'Arrest placed N4882 3 seconds of RA west and 0.3' north of his N4884 which is a duplicate of N4889. Using this offset from N4889 leads to the additional equivalence N4882 =3D N4886.
NGC 5580: Discovered by John Herschel as h1785. There is no galaxy at Herschel's position 14 seconds of RA following and 1' N of his mean position of h1784 = N5579. The RNGC incorrectly identifies N5580 with an anonymous galaxy located 1' S of N5579. N5579 was observed by Herschel on two sweeps but N5580 was observed only on the first sweep. Harold Corwin tentatively suggests that John Herschel's N5580 may be a duplicate observation of N5590 based on the following line of reasoning:
NGC 6197, 6199: These galaxies were discovered by Marth on the same night along with N6196. Regarding N6197 = m312, it was given a poor position by Marth 39 seconds of RA too far west although this is the same offset as he gave N6196. Bigourdan's position for IC 4616 is an exact match with this galaxy and it is identified as IC 4616 in the CGCG, MCG and UGC notes.
The object identified as N6197 in the RNGC is a very faint anonymous galaxy situated 1.3' southwest of N6196. The data listed under N6199 in the RNGC actually describes N6197. Most likely, Marth's N6199 (m313) refers to a single star at the precise position 16 39 28.9 +36 03 31 (2000).
These identifications were discussed by Malcolm Thomson in WSQJ 7/82, and in a letter I wrote to Deep Sky Monthly, Winter 83.
NGC 6039: Discovered by Lewis Swift (see Dreyer's comments in the notes section of NGC). The NGC position is 3.3' south of N6040 and probably corresponds to a faint star. Incorrectly identified in the RNGC and MCG (M+03-41-073) as N6040B, which is the fainter component of the double galaxy N6040. The Arp list of peculiar galaxies lists Arp 122 = N6039 Harold Corwin tentatively identifies N6039 as a star at 16 04 28.4 +17 40 46 (2000) and discussed by Corwin in P.A.S.P. Vol 83, 1971.
NGC 6053: Also discovered by Swift within Abell 2151 (Hercules galaxy cluster). Identified by Harold Corwin in PASP, Vol 83, 1971 as a single star = IC 1180 at 16 05 30.3 +18 08 54 (2000). The RNGC identifies N6053 with a small galaxy 6' south of N6057. This identification is unlikely as Swift's position is over 6' northwest of this object.
NGC 6056: Another Swift entry from Abell 2151. His position is roughly 2' south of the galaxy identified as I1176 (also from Swift) in CGCG (108-122) and MCG (+03-41-100). In the PASP article Corwin states RNGC identifies N6056 as the northeast of two small galaxies SW of N6056 although the RNGC position and new description appears to describe I1176. Actually, Swift's position for I1176 is not good in RA and furthermore his description of "2 st nr s" is not correct unless he observed the two anonymous galaxies to the southwest. Hence, the identification of N6056 = I1176 is uncertain although there is only one reasonably bright galaxy in the vicinity.
NGC 6959, 6965: These galaxies are in the N6962 group. N6959 was discovered at Birr Castle but attributed to Bigourdan in the NGC whose corrected RA is a perfect match. The RNGC misidentifies N6959 with a very faint anonymous galaxy located 1' northwest of the actual N6959. This latter is galaxy is also misidentified in the RNGC as N6965! This galaxy is correctly identified in the UGC notes and CGCG (Z374-013). I discussed this identification in detail in Deep Sky, Fall 1985.
N6965 was also discovered by Lord Rosse at Birr Castle but given imprecise coordinates in the NGC (based on his sketch) which led to a confusion in later catalogues. This galaxy is incorrectly identified in the RNGC, UGC, CGCG, MCG as N6963. The galaxy identified as NG965 in the RNGC is actually N6959. UGC and MCG assign N6965 to N6967.
NGC 7173, 7174, 7176: Although John Herschel gave correct positions for these three galaxies, RNGC has confused the identifications (brightest member N7172 is correctly identified). RNGC reverses the identifications of N7173 and N7174 making N7173 and N7176 the contact pair instead of N7174 and N7176 as described by Herschel.
NGC 7325: Discovered by Herman Schultz in 1874. Schultz's micrometric position and Rosse's offset from N7331 in 1875 both fall precisely on a mag 14/15 double star at 15" separation with one of the components an extremely close double. Harold Corwin gives a position 22 36 49.7 +34 22 06 (2000).
Incorrectly identified in the RNGC as an extremely faint anonymous galaxy about 7' northwest of N7331. On the POSS this galaxy appears to have a fairly bright star superimposed making observation extremely difficult. Discussed in article in Deep Sky, Fall 1986.
NGC 7326: Discovered by Lord Rosse in the Birr Castle observations of N7331. His accurate offset from N7331 of 165" in PA 278.7 points directly at a close double star with GSC position 22 36 52.0 +34 25 22 (2000). Incorrect identified in the RNGC as Z514-066, located 12' northwest of N7331. See article on N7331 companions in Deep Sky, Fall 1986.