Historical Identification: Per Dreyer, NGC 3150 (Bigourdan (list I #40), 1860 RA 10 05 11, NPD 50 39.5) is "very faint, small". The position precesses to RA 10 13 31.6, Dec +38 39 05, about an arcmin east southeast of the galaxy listed above, but Bigourdan's original measurements precess to RA 10 13 27.2, Dec +38 29 21, on the southeastern rim of the galaxy, and its position relative to NGC 3151 (discovered by Bigourdan on the same night) makes the identification of both objects certain.
Discovery Notes: Bigourdan's measurements placed the object 8.6 seconds of time west and 37 arcsec north of an 11th magnitude star he placed at (1900) RA 10 07 39, Dec +39 09. Precessing its position to the equinox of 2000 shows it must have been the 12th magnitude star at J2000 RA 10 13 35.7, Dec +38 38 39. Though supposedly a high proper motion star, its annual motion is only -0.0037" in right ascension and -0.04526" in declination, meaning that in the 114 years between Bigourdan's observation and the FK5 epoch, it had no measurable change in its right ascension and only moved 5 arcsec south in declination, making its 1874 position J2000 10 13 35.7, Dec +38 38 44, which precesses to (1900) RA 10 07 38.8, Dec +39 08 24, nearly the same position used by Bigourdan (so the error in the NGC position must have been due to round-off errors in converting from Bigourdan's 1900 coordinates to the NGC's 1860 coordinates). Adding Bigourdan's offsets and precessing to modern coordinates yields RA 10 13 27.2, Dec +38 39 21, as noted above.
Physical Information: Based on a recessional velocity of 7285 km/sec, a straightforward calculation indicates that NGC 3150 is about 340 million light years away. 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 about 330 million light years away at the time the light by which we see it was emitted, about 335 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 0.95 by 0.7 arcmin (including its fainter outer ring), it is about 90 thousand light years across.

Historical Identification: Per Dreyer, NGC 3151 (Bigourdan (list I #41), 1860 RA 10 05 12, NPD 50 41.2) is "very faint, very small". The position precesses to RA 10 13 32.5, Dec +38 37 23, about 0.7 arcmin east northeast of the galaxy listed above, but Bigourdan's original measurements precess to RA 10 13 28.9, Dec +38 37 12, right on the galaxy, and its position relative to NGC 3150 (discovered by Bigourdan on the same night) makes the identification of both objects certain.
Discovery Notes: Bigourdan used the same comparison star for his #41 as for his #40 (= NGC 3150), so as discussed in that entry the correct position for the comparison star was (1900) RA 10 07 38.8, Dec +39 08 24. Adding his offsets of -6.8 seconds of right ascension and -1' 32" in declination, the nebula should be at (1900) RA 10 07 32.0, Dec +39 06 52, which precesses to J2000 RA 10 13 28.9, Dec +38 37 12, dead center on the galaxy listed above, indicating that as in the case of NGC 3150, the error in the NGC position must have been due to round-off errors in converting from the equinox of 1900 to that of 1860.
Physical Information: Based on a recessional velocity of 6885 km/sec, a straightforward calculation indicates that NGC 3151 is about 320 million light years away. 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 just over 310 million light years away at the time the light by which we see it was emitted, about 315 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 0.55 arcmin, it is between 70 and 75 thousand light years across.

Historical Identification: Per Dreyer, NGC 3152 (= GC 2031, 3rd Lord Rosse, 1860 RA 10 05 16, NPD 50 27.5) is "extremely faint, very small, irregularly round, extremely faint star close to southwest". The position precesses to RA 10 13 37.0, Dec +38 51 04, less than 0.8 arcmin northeast of the galaxy listed above, the description fits save for the fact that the direction of the extremely faint star appears to have been reversed (being to the northeast instead of the southwest), and there is nothing else nearby so the identification is certain.
Discovery Notes: Although Dreyer credits the report of the discovery to William Parsons, 3rd Earl of Rosse, he notes that many of Rosse's nebular discoveries were actually made by his assistants, George Stoney, Bindon Stoney and R. J. Mitchell.
Physical Information: Based on a recessional velocity of 6405 km/sec, NGC 3152 is about 300 million light years away. Given that and its apparent size of 0.7 by 0.6 arcmin, it is about 60 thousand light years across.

Historical Identification: Per Dreyer, NGC 3153 (= GC 2026 = WH III 53 = JH 677, Peters, 1860 RA 10 05 22, NPD 76 38.8) is "extremely faint, pretty large, very little extended, mottled but not resolved, star involved". The position precesses to RA 10 12 52.4, Dec +12 39 48, on the eastern rim of the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Discovery Notes: Todd's observation was #20b in a list of nebulae he noticed while searching for a trans-Neptunian planet. Some were new discoveries, but many were not, and were left unmentioned by Dreyer.
Physical Information: Based on a recessional velocity of 2810 km/sec, NGC 3153 is about 130 million light years away, in good agreement with redshift-independent distance estimates of 80 to 180 million light years. Given that and its apparent size of 2.1 by 0.9 arcmin, it is about 80 thousand light years across.

Historical Identification: Per Dreyer, NGC 3154 (Stephan list X (#24), 1860 RA 10 05 24, NPD 72 16.5) is "faint, small, round, a little brighter middle". The position precesses to RA 10 13 01.5, Dec +17 02 05, dead center on the galaxy listed above and there is nothing comparable nearby, so the identification is certain.
Physical Information: Based on a recessional velocity of 6600 km/sec, NGC 3154 is 305 to 310 million light years away. Given that and its apparent size of 0.9 by 0.4 arcmin, it is about 80 thousand light years across.

Historical Identification: Per Dreyer, NGC 3155 (= GC 2033 = JH 676, d'Arrest, 1860 RA 10 05 24, NPD 14 58.1) is "very faint, small, round". The position precesses to RA 10 17 45.5, Dec +74 20 16, about 0.7 arcmin southeast of the center of the galaxy listed above, and about half that distance from its southeastern outline. The description is reasonable and there is nothing else nearby, so the identification is certain.
Discovery Notes: As discussed here, Herschel's observations of Apr 2, 1801 were made with his telescope out of alignment with the meridian, making the fifteen nebulae he discovered on that night difficult or impossible to identify; as a result his observation of this object ended up as NGC 3194, which see for a discussion of the duplicate entry. (Dreyer's 1912 revision of the NGC based on his reassessment of William Herschel's papers included the notes "3155 is = (WH) III 965", and "3194 to be struck out (= 3155)", so the fact that NGC 3194 was a duplicate entry has been known for more than a century.)
Physical Information: Based on a recessional velocity of 2945 km/sec, NGC 3155 is about 135 million light years away, in reasonable agreement with redshift-independent distance estimates of 140 to 185 million light years. Given that and its apparent size of 1.4 by 0.7 arcmin, the galaxy is about 55 thousand light years across.

Historical Identification: Per Dreyer, NGC 3156 (= GC 2028 = JH 680 = WH III 255, 1860 RA 10 05 26, NPD 86 10.6) is "faint, considerably small, round, pretty suddenly brighter middle, 9th or 10th magnitude star 2 arcmin to southeast". The position precesses to RA 10 12 41.6, Dec +03 08 00, within the northern outline of the galaxy listed above, there is nothing else nearby and the star to the southeast makes the identification certain.
Physical Information: Based on a recessional velocity of 1340 km/sec, NGC 3156 is about 60 to 65 million light years away, in good agreement with redshift-independent distance estimates of 40 to 85 million light years. Given that and its apparent size of 1.9 by 0.85 arcmin, the galaxy is about 35 thousand light years across.

Historical Identification: Per Dreyer, NGC 3157 (= GC 2029 = JH 3233, 1860 RA 10 05 28, NPD 120 16.1) is "very faint, pretty small, extended, 8th or 9th magnitude star to southwest". The position precesses to RA 10 11 46.6, Dec -30 57 27, but there is nothing there save for a completely stellar field. However (per Corwin), the problem was a simple mistake in precessing and transcribing the original Cape of Good Hope position to the GC (and from there, to the NGC); the original position of (1830) 10 04 06.7, NPD 120 47 15 precesses to RA 10 11 44.5, Dec -31 37 23, forty arcmin south of the NGC position, but only 1.2 arcmin north northeast of the center of the galaxy listed above and less than half that distance from its northern outline, the description fits and the 9th magnitude star to the south southwest makes the identification certain. Of course the large error in the declination made it inevitable that later observers would think they had found a new nebula, hence the duplicate entry, for which see IC 2555.
Physical Information: Based on a recessional velocity of 2840 km/sec, NGC 3157 is about 130 to 135 million light years away, in good agreement with redshift-independent distance estimates of 95 to 145 million light years. Given that and its apparent size of 2.4 by 0.5 arcmin, the galaxy is 90 to 95 thousand light years across.

Historical Identification: Per Dreyer, NGC 3158 (= GC 2030 = JH 678 = WH II 639, 1860 RA 10 05 30, NPD 50 32.6) is "considerably bright, considerably small, round, pretty suddenly brighter middle, mottled but not resolved". The position precesses to RA 10 13 50.7, Dec +38 45 57, practically dead center on the galaxy listed above, the description fits and there is nothing comparable nearby so the identification is certain.
Physical Information: Based on a recessional velocity of 6990 km/sec, a straightforward calculation indicates that NGC 3158 is about 325 million light years away. 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 about 315 million light years away at the time the light by which we see it was emitted, about 320 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 1.7 by 1.2 arcmin, the bright central portion of the galaxy is about 155 thousand light years across, but it has a faint halo spanning 3.5 by 3.1 arcmin, which corresponds to about 320 thousand light years, making it a sub-giant elliptical.

Historical Identification: Per Dreyer, NGC 3159 (Bigourdan (list I #42), 1860 RA 10 05 35, NPD 50 38.9) is "very faint, very small, stellar". The position precesses to RA 10 13 55.4, Dec +38 39 38, about 0.6 arcmin northeast of the galaxy listed above, and although that lies between that galaxy and the one to its east, the other one is accounted for by NGC 3161, so the identification is essentially certain. As it happens, the error in right ascension is due to rounding off the conversion from the equinox of 1900 to that of 1860, as Bigourdan's original measurements (discussed immediately below) average 0.8 arcmin due south of the galaxy listed above, removing any doubt about which galaxy should be NGC 3159.
Discovery Notes: Bigourdan used the same comparison star for his #42 as for his #40 (= NGC 3150), so as discussed in that entry the correct position for the comparison star was (1900) RA 10 07 38.8, Dec +39 08 24. Adding his offsets of +17.6 seconds of time in right ascension and +42 arcsec in declination, the object should be at (1900) RA 10 07 56.4, Dec +39 09 06, which precesses to J2000 RA 10 13 53.2, Dec +38 38 25, due south of the galaxy listed above.
Physical Information: Based on a recessional velocity of 6805 km/sec, a straightforward calculation indicates that NGC 3159 is about 315 million light years away, in good agreement with redshift-independent distance estimates of 215 to 360 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 just under 310 million light years away at the time the light by which we see it was emitted, just over 310 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 0.55 by 0.45 arcmin, the galaxy is about 50 thousand light years across.

Historical Identification: Per Dreyer, NGC 3160 (= GC 2032, 3rd Lord Rosse, 1860 RA 10 05 35, NPD 50 27.8) is "very faint, very small, a little extended". The position precesses to RA 10 13 55.8, Dec +38 50 44, just off the northeastern rim of the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Discovery Notes: Although Dreyer credits the report of the discovery to William Parsons, 3rd Earl of Rosse, he notes that many of Rosse's nebular discoveries were actually made by his assistants, George Stoney, Bindon Stoney and R. J. Mitchell. (Dreyer's 1877 supplement to the GC lists the position as 1860 RA 10 05 32. There is no indication of whether the change in the NGC is a typographical error or a correction to the earlier publication, but the NGC position falls very close to the nucleus of the galaxy, whereas the earlier position, which lies off the northwestern arm of the galaxy, is further from the nucleus; so the change was probably deliberate.)
Physical Information: Based on a recessional velocity of 6920 km/sec, a straightforward calculation indicates that NGC 6920 is 320 to 325 million light years away. 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 310 to 315 million light years away at the time the light by which we see it was emitted, about 315 to 320 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 1.35 by 0.3 arcmin, the galaxy is 120 to 125 thousand light years across.

Historical Identification: Per Dreyer, NGC 3161 (Bigourdan (list I #43), 1860 RA 10 05 38, NPD 50 38.9) is "very faint, very small". The position precesses to RA 10 13 58.4, Dec +38 39 38, less than 0.3 arcmin northwest of the center of the galaxy listed above and despite its small size barely outside its northwestern rim, and there is nothing comparable nearby save for other objects observed by Bigourdan on the same night, so the identification is certain. (Referring to Bigourdan's original measurements (as shown below) moves the position slightly to the south and even closer to the galaxy, but is not required for a certain identification.)
Discovery Notes: Bigourdan used the same comparison star for his #43 as for his #40 (= NGC 3150), so as discussed in that entry the correct position for the comparison star was (1900) RA 10 07 38.8, Dec +39 08 24. Adding his offsets of +22.8 seconds of time in right ascension and +48 arcsec in declination, the object should be at (1900) RA 10 08 01.6, Dec +39 09 12, which precesses to J2000 RA 10 13 58.4, Dec +38 39 30, eight arcsec due south of the NGC position, less than 0.2 arcmin from the center of the galaxy and on its northwestern outline; but makes no significant difference in the certainty of the identification.
Physical Information: Based on a recessional velocity of 6285 km/sec, NGC 3161 is about 290 to 295 million light years away. Given that and its apparent size 0.65 by 0.45 arcmin, it is about 55 thousand light years across.

Historical Identification: Per Dreyer, NGC 3162 (= GC 2034 = JH 682 = WH II 43, 1860 RA 10 05 44, NPD 66 34.3) is "pretty faint, considerably large, round, very gradually a little brighter middle, mottled but not resolved, small (faint) star involved". The position precesses to RA 10 13 31.2, Dec +22 44 15, almost dead center on the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain. (For a discussion of the error in d'Arrest's position that led to the duplicate entry, see NGC 3575.)
Physical Information: Based on a recessional velocity of 1300 km/sec, NGC 3162 is about 60 million light years away, in fair agreement with redshift-independent distance estimates of 70 to 95 million light years. Given that and its apparent size of 3.0 by 2.4 arcmin, it is about 55 thousand light years across.

Historical Identification: Per Dreyer, NGC 3163 (= GC 2035 = JH 681 = WH II 640, 1860 RA 10 05 48, NPD 50 40.2) is "faint, small, round, gradually brighter middle". The position precesses to RA 10 14 08.2, Dec +38 38 19, about 0.8 arcmin south southeast of the galaxy listed above, the description fits and there is nothing comparable nearby save for the "novae" observed by Bigourdan on the same night (most significantly NGC 3159 and 3161), so the identification is certain.
Discovery Notes: Bigourdan's offsets for NGC 3163 were from the same comparison star used for his "novae", but are not as accurate (perhaps because of the greater distance from the star), and do not improve on the Herschels' position. Still, they definitely place NGC 3163 to the east of NGC 3161, and the only thing to the east of that galaxy is the one listed above, so they do help confirm that identification.
Physical Information: Based on a recessional velocity of 6260 km/sec, NGC 3163 is about 290 million light years away, in good agreement with redshift-independent distance estimates of 185 to 355 million light years. Given that and its apparent size of 1.4 by 1.05 arcmin, it is about 120 thousand light years across.

Historical Identification: Per Dreyer, NGC 3164 (= GC 2036 = JH 679, 1860 RA 10 05 49, NPD 32 38.8) is "extremely faint, small, round, very gradually a little brighter middle". The position precesses to RA 10 15 11.8, Dec +56 39 40, about 0.7 arcmin due south of the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Physical Information: Based on a recessional velocity of 7820 km/sec, a straightforward calculation indicates that NGC 3164 is about 365 million light years away. 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 about 355 million light years away at the time the light by which we see it was emitted, about 360 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 1.4 by 0.7 arcmin, it is about 145 thousand light years across.

Historical Identification: Per Dreyer, NGC 3165 (= GC 2037, 3rd Lord Rosse, Stephan list XIII, 1860 RA 10 06 00, NPD 85 55.5) is "very faint, much extended 0°, 1st of 3", the others being NGC 3166 and 3169. The position precesses to RA 10 13 15.9, Dec +03 23 03, almost 4 arcmin west northwest of the galaxy listed above, but the description fits (including the "1st of 3") and there is nothing else nearby, so the identification is certain. (Mitchell's observation stated "About 5 arcmin southwest of 684 (= NGC 3166) is a very very faint ray extended north-south"; taking that at face value yields a position near the southern rim of the galaxy listed above, so the error in the NGC position is not due to Mitchell's observation, but an incorrect reduction of the observation to a specific position.)
Discovery Notes: Although Dreyer credits the report of the discovery to William Parsons, 3rd Earl of Rosse, he notes that many of Rosse's nebular discoveries were actually made by his assistants, George Stoney, Bindon Stoney and R. J. Mitchell. Also, Dreyer's reference to Stephan's list XIII is an error, as Stephan's observations of the region correspond to the 2nd and 3rd of the 3 nebulae involved, and he apparently could not see the much fainter NGC 3165 (unfortunately, Dreyer's error still lives on in Steinicke's 2015 database).
Physical Information: Based on a recessional velocity of 1340 km/sec, NGC 3165 is 60 to 65 million light years away. Given that and its apparent size of 1.3 by 0.6 arcmin, it is about 25 thousand light years across.

Historical Identification: Per Dreyer, NGC 3166 (= GC 2038 = JH 684 = WH I 3, 1860 RA 10 06 30, NPD 85 53.0) is "bright, pretty small, round, pretty suddenly much brighter middle, 2nd of 3", the others being NGC 3165 and 3169. The position precesses to RA 10 13 46.0, Dec +03 25 30, right on the galaxy listed above, the description fits (including "2nd of 3") and there is nothing comparable nearby save for the galaxies making up the "of 3", so the identification is certain.
Discovery Notes: Stephan's observation is his list XIII #56, which precesses to 1860 RA 10 06 29.8, NPD 85 53.1; it is the observation mistakenly attributed by Dreyer (and Steinicke) to NGC 3165, which must have been too faint for Stephan to see.
Physical Information: Based on a recessional velocity of 1345 km/sec, NGC 3166 is about 60 to 65 million light years away, in reasonable agreement with a single redshift-independent distance estimates of 70 million light years. Given that and its apparent size of 4.7 by 2.1 arcmin, it is about 85 thousand light years across. The galaxy is strongly interacting with NGC 3169, with considerable distortion of each galaxy as a result of their interaction.

Historical Identification: Per Dreyer, NGC 3167 (= GC 2039, d'Arrest, 1860 RA 10 06 37, NPD 59 42.7) is "faint, small, perhaps very small cluster of very faint stars". The position precesses to RA 10 14 36.8, Dec +29 35 45, but there is nothing there nor near there. The key to identifying the object (per Corwin) is d'Arrest's mention of a magnitude 11 star 9.5 seconds of time to the west, and very slightly north. This agrees with the region near NGC 2789, which has an 1860 RA exactly 1 hour smaller, suggesting a typographical error by d'Arrest in recording that coordinate. Using an 1860 RA of 09 06 37 the position precesses to RA 09 15 00.0, Dec +29 42 42, only an arcmin south of the galaxy listed above, and the aforementioned star makes the identification as a duplicate of NGC 2789 certain.
Discovery Notes: Because of the large error in d'Arrest's position, NGC 3167 was thought to be a lost or nonexistent object into the early 21st century; as a result, LEDA has an entry ("PGC 5067762") for that "unknown" object, albeit with a designation that is not recognized by a search of the LEDA database.
Physical Information: Given the duplicate entry, see NGC 2789 for anything else.

Historical Identification: Per Dreyer, NGC 3168 (= GC 2040 = JH 683, 1860 RA 10 06 45, NPD 29 04.6) is "faint, pretty suddenly brighter middle, stellar, 7th or 8th magnitude star 5 arcmin to northwest". The position precesses to RA 10 16 26.4, Dec +60 13 46, only half an arcmin southeast of the galaxy listed above, the description fits and there is nothing else nearby save for the 7th magnitude star just over 5 arcmin to the south southwest which, given the frequency with which such directions are mis-stated (due to the inversion of images in telescopic views varying according to the type of eyepiece in use), makes the identification certain.
Physical Information: Based on a recessional velocity of 9450 km/sec, a straightforward calculation indicates that NGC 3168 is about 440 million light years away. 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 about 425 million light years away at the time the light by which we see it was emitted, about 430 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 0.9 by 0.9 arcmin, the galaxy is about 110 thousand light years across.

Historical Identification: Per Dreyer, NGC 3169 (= GC 2041 = JH 685 = WH I 4, 1860 RA 10 06 59, NPD 85 50.5) is "bright, pretty large, very little extended, pretty gradually much brighter middle, 11th magnitude star 80 arcsec distant at position angle 78°, 3rd of 3", the others being NGC 3165 and 3166. The position precesses to RA 10 14 15.0, Dec +03 27 57, essentially dead center on the galaxy listed above, the description fits (including the 11th magnitude star on its eastern periphery) and there is nothing nearby save for the others "of 3", so the identification is certain.
Discovery Notes: Stephan's observation is his list XIII #57, which precesses to 1860 RA 10 06 59.3, NPD 85 50.5. (Unfortunately, misattributed to NGC 3166 in Steinicke's 2015 catalog.)
Physical Information: Based on a recessional velocity of 1240 km/sec, NGC 3169 is 55 to 60 million light years away, in reasonable agreement with widely varying redshift-independent distance estimates of 50 by 175 million light years. Given that and its apparent size of 7.5 by 5.0 arcmin, it is about 125 thousand light years across, though large patches and arcs of gas and stars are scattered across a region spanning 14 by 9 arcmin, corresponding to 235 thousand light years, due to its strong interaction with NGC 3166.

Historical Identification: Per Dreyer, NGC 3170 (= GC 2042 = JH 686, 1860 RA 10 07 32, NPD 42 42.7) is "faint, small, round". The position precesses to RA 10 16 13.3, Dec +46 35 38, in a completely stellar field. However (per Corwin), the description perfectly fits the double star just over an arcmin nearly due north of the NGC position, and Herschel (and for that matter many other observers) often mistook such close doubles for nebulae, so the identification is essentially certain. Listed in LEDA as a double star with the designation PGC 5067739, but a search of the database for that entry returns no results.

Historical Identification: Per Dreyer, NGC 3171 (Ormond Stone list I (#169), 1860 RA 10 07 35, NPD 109 56.1) is "extremely faint, small, round, gradually brighter middle". The position precesses to RA 10 14 13.6, Dc -20 37 41, in a completely stellar field. However, the McCormick Leander Observatory was notorious for its often large errors in right ascension, and there is an appropriate candidate less than a minute and half of time nearly due east of the NGC position (namely the galaxy listed above) and nothing comparable in a much larger region, so the identification is reasonably certain.
Physical Information: Based on a recessional velocity of 3565 km/sec, NGC 3171 is about 165 million light years away. Given that and its apparent size of 2.0 by 1.2, it is about 95 thousand light years across.

Historical Identification: Per Dreyer, NGC 3172 (= GC 2043 = JH 250, 1860 RA 10 08±, NPD 00 06.8) is "very faint, round, gradually brighter middle, 11th magnitude star 2 arcmin to south, Polarissima Borealis", the appellation referring to the fact that it was the northernmost nebula in the sky at that time (being less than 7 arcmin from the North Celestial Pole), but precession is gradually moving it further from the Pole, and by the end of 2016 it will be over a degree from the Pole. A note at the end of the NGC states "This nebula is so near the Pole that its R.A. is necessarily a very rude approximation. d'Arrest found RA 09 39" (d'Arrest's almost equally "rude approximation" was actually (1861) RA 09 44??, Dec +89 51.7 = (1860) RA 09 38.6, Dec +89 52.0, and stated that a 12th magnitude star was about 75 arcsec to the north). The corrected position precesses to J2000 RA 11 44.1, Dec +89 06.4, only an arcmin northwest of the galaxy listed above and there is nothing comparable nearby, so the 13th magnitude star about 90 arcsec to the northwest makes the identification certain.
Physical Information: Based on a recessional velocity of 6095 km/sec, NGC 3172 is about 285 million light years away. Given that and its apparent size of 1.05 by 1.05 arcmin, it is about 85 thousand light years across. There is a possibility that there are very faint extensions of the galaxy scattered across a region over 3 arcmin wide, perhaps as a result of an interaction with the fainter galaxy (PGC 36268) to the west (unfortunately, even less is known about that object, so whether it is a true companion or merely an optical double is unknown). So the description and size of NGC 3172 may be considerably altered when it is subjected to further study.
Image Note: The images below are shown with North at the top as of the equinox of 2000; but since the region is so close to the Pole, most images show North in another (almost invariably wrong) direction. Even the ESO DSS image, which usually has North at the top, has North down and to the left (this can be verified by entering different declinations for the image, and seeing how that changes the position of objects in the field of view), and the identical image on the NGCIC Project site shows an arrow for North that is actually pointing due South.

Physical Information: Based on possible faint extensions surrounding NGC 3172, PGC 36268 may be interacting with it, hence its inclusion here, instead of on the corresponding PGC page. It has an apparent size of 0.45 by 0.35 arcmin, but nothing else is known about it, so whether it is actually a companion of the larger galaxy or merely in the same direction is also unknown.

Historical Identification: Per Dreyer, NGC 3173 (= GC 2044 = JH 3235, 1860 RA 10 08 09, NPD 116 59.7) is "extremely faint, small, round, two bright stars to the east". The position precesses to RA 10 14 35.1, Dec -27 41 19, well within the outline of the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Physical Information: Based on a recessional velocity of 2520 km/sec, NGC 3173 is 115 to 120 million light years away. Given that and its apparent size of 2.2 by 1.9 arcmin, it is about 75 thousand light years across.

Historical Identification: Per Dreyer, NGC 3174 (= GC 2045 = WH III 964, 1860 RA 10 08 16, NPD 14 38.6) is "considerably faint, small, stellar, small star near to east [Place very questionable]". The position precesses to RA 10 20 36.8, Dec +74 39 30, in a completely stellar field. However, although Dreyer made no comment about GC 2045 in his 1877 Supplement to the General Catalog, by the time he compiled the NGC he was aware of the fact that all of Herschel's observations of Apr 2, 1801 suffered from some large, inexplicable error (hence "Place very questionable"). As discussed here, that led him to request (in the early 1900's) that the Astronomer Royal take photographic plates of the region observed by Herschel on that night, and as a result Dreyer's 1912 revision of the NGC included the notes "3144 is = (WH) III 964", and "3174 to be struck out (= 3144)", so the correct identification (and duplicate entry) has been known for more than a century.
Discovery Notes: Although Dreyer was able to identify what Herschel observed, it was not until 2011-12 that Wolfgang Steinicke showed that the problem was due to the observations of the date in question having been made with the telescope 7 degrees out of alignment with the meridian, causing reductions of the measurements based on the assumption that it was aligned with the meridian to be badly askew (as discussed in the note mentioned above).
Physical Information: Given the duplicate entry, see NGC 3144 for anything else. (Note that d'Arrest's description of the object is nearly identical to Herschel's, most notably with reference to the faint star just east of the galaxy, making the identification of NGC 3174 as a duplicate of NGC 3144 absolutely certain.)

Historical Identification: Per Dreyer, NGC 3175 (= GC 2046 = JH 3236, 1860 RA 10 08 19, NPD 118 11.1) is "considerably bright, large, much extended 51°, very gradually a little brighter middle". The position precesses to RA 10 14 42.9, Dec -28 52 44, on the southeastern rim of the galaxy listed above, the description fits and there is nothing comparable nearby so the identification is certain.
Physical Information: Based on a recessional velocity of 1100 km/sec (and H₀ = 70 km/sec/Mpc), NGC 3175 is just over 50 million light years away, in good agreement with redshift-independent distance estimates of 45 to 90 million light years (the HST press release says "around 50 million light years"). Given that and its apparent size of about 5.0 by 1.5 arcmin (from the images below), it is 75 thousand light years across.

Historical Identification: Per Dreyer, NGC 3176 (Ormond Stone list I (#170), 1860 RA 10 08 35, NPD 108 20.1) is "extremely faint, pretty small, irregularly round, perhaps nebulous". The position precesses to RA 10 15 16.5, Dec -19 01 46, but there is nothing in the completely stellar field near that position that is in any way nebulous. (As a check we can refer to Stone's original observation, which states that the object has magnitude 16.0, a diameter of 0.8 arcmin, is irregularly round, perhaps nebulous, and located at (1890) RA 10 10, Dec -18 29. This precesses to RA 10 15 15.6, Dec -19 01 47 (whence the position listed above), which is essentially the same as the NGC position.) Sometimes it is possible to find Leander McCormick Observatory objects by looking to the east or west of their recorded position, but in this case there is nothing anywhere along its parallel of declination, so whatever Stone saw was probably just a close pair of stars or a very small asterism that would be impossible to identify, hence its listing here as lost or nonexistent. However, PGC 29907 is sometimes listed as NGC 3176, so it is discussed immediately below.

Historical Identification: As discussed in the entry for NGC 3176, that is probably a lost or nonexistent object. However, if we assume that Stone's declination was off by a degree (in other words, (1890) -19 29, instead of -18 29), the position precesses to RA 10 15 14.3, Dec -20 01 47, a little over 5 arcmin east southeast of the galaxy listed above. Such an error in position would be unusual but not unprecedented, so PGC 29907 is sometimes listed as NGC 3176, though almost always with a warning about the uncertainty of the identification.
Physical Information: Based on a recessional velocity of 3330 km/sec, PGC 29907 is about 155 million light years away. Given that and its apparent size of 0.55 by 0.55 arcmin, it is about 25 thousand light years across.

Historical Identification: Per Dreyer, NGC 3177 (= GC 2047 = JH 687 = WH III 25, 1860 RA 10 08 52, NPD 68 10.7) is "considerably faint, small, round, pretty suddenly brighter middle". The position precesses to RA 10 16 35.5, Dec +21 07 34, within the northeastern outline of the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Physical Information: Based on a recessional velocity of 1300 km/sec, NGC 3177 is about 60 million light years away, in fair agreement with redshift-independent distance estimates of 70 to 85 million light years. Given that and its apparent size of 1.3 by 1.25 arcmin, it is about 20 to 25 thousand light years across.

Historical Identification: Per Dreyer, NGC 3178 (= GC 2048 = JH 3237, 1860 RA 10 09 24, NPD 105 05.9) is "pretty bright, pretty large, gradually pretty much brighter middle". The position precesses to RA 10 16 11.0, Dec -15 47 39, on the southeastern rim of the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Physical Information: Based on a recessional velocity of 3485 km/sec, NGC 3178 is about 160 to 165 million light years away, in good agreement with redshift-independent distance estimates of 155 to 170 million light years. Given that and its apparent size of 1.45 by 0.9 arcmin, it is about 70 thousand light years across.

Historical Identification: Per Dreyer, NGC 3179 (3rd Lord Rosse, 1860 RA 10 09 30, NPD 48 15) is "small, round, brighter middle and nucleus, in line with 2 stars". The second IC adds "= Bigourdan 277, RA 10 09 33, NPD 48 11". Stoney's position isn't bad, but Bigourdan's is even better, precessing to RA 10 17 57.2, Dec +41 07 10, less than 0.3 arcmin from the center of the galaxy listed above and barely above its nuclear region, the description fits and there is nothing else nearby so the identification is certain.
Discovery Notes: Although Dreyer credits the report of the discovery to William Parsons, 3rd Earl of Rosse, he notes that many of Rosse's nebular discoveries were actually made by his assistants, George Stoney, Bindon Stoney and R. J. Mitchell.
Physical Information: Based on a recessional velocity of 7260 km/sec, a straightforward calculation indicates that NGC 3179 is about 340 million light years away, in reasonable agreement with redshift-independent distance estimates of 350 to 405 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 325 to 330 million light years away at the time the light by which we see it was emitted, 330 to 335 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 about 1.6 by 0.45 arcmin, the galaxy is 150 to 155 thousand light years across.

Historical Identification: Per Dreyer, NGC 3180 (= GC 2049, 3rd Lord Rosse, 1860 RA 10 09 45, NPD 47 53.2) is "very faint, extended, (and along with NGC 3181) connected with h688", h688 being NGC 3184. The position precesses to RA 10 18 09.8, Dec +41 24 57, within NGC 3184 (matching the description), but almost 2 arcmin south of the region listed above. The key to identifying which part of NGC 3184 is NGC 3180 is a sketch published as plate XXVII figure 13 of the Philosophical Transactions of the Royal Astronomical Society of 1861 (shown below, as retrieved from the Internet Archive), showing the relative positions of NGC 3180 and 3181 on one of NGC 3184's spiral arms, and a note of Feb 26, 1851 stating that the "preceding" part (NGC 3180) is "probably (a) portion of a ring". Given that, there is no doubt that NGC 3180 is the U-shaped group of star-forming regions shown in the second image of the entry for NGC 3184.
Discovery Notes: Although Dreyer credits the report of the discovery to William Parsons, 3rd Earl of Rosse, he notes that many of Rosse's nebular discoveries were actually made by his assistants, George Stoney, Bindon Stoney and R. J. Mitchell.
Physical Information: Per Corwin, the northeast portion of the "ring" lies at RA 10 18 10.7, Dec +41 26 54, and the southwest portion at RA 10 18 08.5, Dec +41 26 27. The apparent size of the U-shaped region is about 0.75 by 0.45 arcmin, and given NGC 3184's distance of 25 to 30 million light years, that corresponds to about 6 thousand light years. Listed in LEDA as galaxy part PGC 3518629, but a search for that designation returns no result.

Historical Identification: Per Dreyer, NGC 3181 (= GC 2050, 3rd Lord Rosse, 1860 RA 10 09 47, NPD 47 54.2) is "very faint, extended, (and along with NGC 3180) connected with h688", h688 being NGC 3184. The position precesses to RA 10 18 11.8, Dec +41 23 57, within NGC 3184 (matching the description), about 0.8 arcmin south of the region listed above. As in the case of NGC 3180, the key to identifying which part of NGC 3184 is NGC 3180 is a sketch Mitchell made (published as plate XXVII figure 13 of the Philosophical Transactions of the Royal Astronomical Society of 1861), showing the relative positions of NGC 3180 and 3181 on one of NGC 3184's spiral arms. Given that, the identification of NGC 3181 as the brightest part of the southwestern portion of the spiral arm is essentially certain.
Discovery Notes: Although Dreyer credits the report of the discovery to William Parsons, 3rd Earl of Rosse, he notes that many of Rosse's nebular discoveries were actually made by his assistants, George Stoney, Bindon Stoney and R. J. Mitchell.
Physical Information: The apparent size of NGC 3181 is about 0.3 by 0.2 arcmin, and given NGC 3184's distance of 25 to 30 million light years, that corresponds to about 2500 light years. For a labeled version of Mitchell's sketch of NGC 3184, showing the position of NGC 3180 and 3181, see NGC 3180; for a labeled photograph showing the star-forming regions, see NGC 3184. Listed in LEDA as galaxy part PGC 3517701, but a search for that designation returns no result.

Historical Identification: Per Dreyer, NGC 3182 (= GC 2051 = WH I 265, 1860 RA 10 09 48, NPD 31 05.7) is "considerably bright, considerably large, irregularly round, very gradually brighter middle". The position precesses to RA 10 19 14.2, Dec +58 12 24, about 2.5 arcmin west of the galaxy listed above, but the description fits and there is nothing else nearby so the identification is certain.
Physical Information: Based on a recessional velocity of 2120 km/sec, NGC 3182 is 95 to 100 million light years away. Given that and its apparent size of 1.8 by 1.4 arcmin, it is about 50 thousand light years across. NGC 3182 is usually classified as an early-type spiral galaxy, but in the images below it appears to be a lenticular galaxy with a bright central ring similar to those found in the nuclei of starburst galaxies, hence the type listed above.

Historical Identification: Per Dreyer, NGC 3183 (= GC 5523, d'Arrest, 1860 RA 10 09 48, NPD 15 07.1) is "faint, pretty large, extended, a little brighter middle". The position precesses to RA 10 21 55.0, Dec +74 10 53, on the eastern arm of the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Discovery Notes: Although d'Arrest's position was good, Herschel's observations of Apr 2, 1801 were made with his telescope out of alignment with the meridian, making the fifteen nebulae he discovered on that night difficult or impossible to identify. Dreyer's 1912 revision of the NGC based on his reassessment of William Herschel's papers resolved the situation by including the notes "3183 is = (WH) I 283", and "3218 to be struck out (= 3183)"; but see NGC 3218 for more about the double listing.
Physical Information: Based on a recessional velocity of 3090 km/sec, NGC 3183 is about 145 million light years away, in good agreement with redshift-independent distance estimates of 120 to 145 million light years. Given that and its apparent size of 2.4 by 1.3 arcmin, it is about 100 thousand light years across.

Historical Identification: Per Dreyer, NGC 3184 (= GC 2052 = GC 2053 = JH 688 = JH 689 = WH I 168, 1860 RA 10 09 50, NPD 47 53.0) is "pretty bright, very large, round, very gradually brighter middle". The position precesses to RA 10 18 14.8, Dec +41 25 09, right on the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Discovery Notes: A note at the end of the NGC discusses the equality of JH 688 and 689: "h689 was looked for in vain by Winnecke in 1876. It is marked as uncertain in both co-ordinates, and is therefore = h688. Only one was seen at Birr, although in P.T. 1861 the descriptions are erroneously given as belonging to two different objects".
Physical Information: Based on a recessional velocity of 590 km/sec, NGC 3184 is 25 to 30 million light years away, in reasonable agreement with redshift-independent distance estimates of 25 to 55 million light years. Given that and its apparent size of 7.0 by 6.6 arcmin, it is about 55 thousand light years across. NGC 3180 and 3181 are ionized hydrogen clouds associated with star-forming egions in NGC 3184. NGC 3181 is the bright region southwest of the nucleus, on the inner spiral arm. NGC 3180 is the two bright regions further out on that arm, northwest of the nucleus.

Historical Identification: Per Dreyer, NGC 3185 (= GC 2054, 3rd Lord Rosse, d'Arrest, 1860 RA 10 09 55, NPD 67 36.8) is "pretty faint, pretty large, gradually much brighter middle". The position precesses to RA 10 17 39.1, Dec +21 41 22, right on the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Discovery Notes: Although Dreyer credits the report of the discovery to William Parsons, 3rd Earl of Rosse, he notes that many of Rosse's nebular discoveries were actually made by his assistants, George Stoney, Bindon Stoney and R. J. Mitchell. Also, although Dreyer appears to have been unaware of Schönfeld's observation, he independently discovered the object as noted above.
Physical Information: Based on a recessional velocity of 1215 km/sec, NGC 3185 is about 55 million light years away, in good agreement with widely varying redshift-independent distance estimates of 35 to 90 million light years. However, as a member of Hickson Compact Group 44 it probably has a distance corresponding to the average recessional velocity of the group, which is about 1360 km/sec (in which case its peculiar velocity relative to the average radial velocity of the Group would be about 145 km/sec), which corresponds to a distance of 60 to 65 million light years. Given that and its apparent size of 2.9 by 1.9 arcmin (counting its faint outer ring), it is about 55 thousand light years across. NGC 3185 is listed as a Seyfert galaxy (type Sy 2), as a result of matter interacting with a supermassive black hole in its center. It is a member of Hickson Compact Group 44. The Group is relatively close to us, so it spans nearly 18 arcmin, and was listed as a compact group because of its small physical size, not its apparent size.

Historical Identification: Per Dreyer, NGC 3186 (= GC 5524, Marth 195, 1860 RA 10 09 57, NPD 82 15) is "pretty faint, very small, gradually brighter middle, several faint stars near". The position precesses to RA 10 17 18.2, Dec +07 03 11 (whence the position above), but there is nothing matching the description near the position. There are two candidates that have received some support (as shown in the following entries), but whether either is what Marth saw is not obvious, and there is no good way to choose between them. For instance (per Corwin), Marth's description did not include "several faint stars near", there is no indication of why Dreyer added that to the description in his 1877 supplement to the GC or the corresponding NGC entry, and even if correct the addendum is too vague to help identify what Marth saw, so it is probably most accurate to list NGC 3186 as lost or nonexistent, as I have done in this entry.

Historical Identification: As noted in the entry for NGC 3186 there is nothing near the NGC position for that object; but there is a galaxy about 7 arcmin to the southeast (almost 5 arcmin to the south and a similar distance to the east of the NGC position) that might be what Marth saw. For the usually very precise Marth that would be an exceptionally large and unusual error (a typographical error in only one coordinate being far more likely), and (per Corwin) none of the other objects found by Marth on the night in question had significant errors, so it is hard to justify identifying PGC 30058 as NGC 3186. Still, Corwin reluctantly concedes the possibility, and LEDA long ago accepted the 1973 RNGC's identification of PGC 30058 as NGC 3186, so even though the galaxy was probably chosen by Sulentic and Tifft merely because it was the closest reasonably bright object to the NGC position, the reader may occasionally run into this identification. For that reason, whether the identification is miraculously correct or completely wrong, it is necessary to at least mention it here.
Physical Information: Based on a recessional velocity of 13545 km/sec, a straightforward calculation indicates that PGC 30058 is about 630 million light years away. 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 about 600 million light years away at the time the light by which we see it was emitted, about 610 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 0.75 by 0.65 arcmin, the galaxy is about 130 thousand light years across. PGC 30058 is listed as a Seyfert galaxy (type Sy 1). Given the galaxy's distorted appearance, see PGC 1311290 for a discussion of possible interactions with that apparent companion.

Physical Information: Based on a recessional velocity of 13990 km/sec, a straightforward calculation indicates that PGC 1311290 is about 650 million light years away. 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 about 615 million light years away at the time the light by which we see it was emitted, about 630 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 0.3 by 0.15 arcmin, the galaxy is about 55 thousand light years across. Despite the difference of 15 million light years in the Hubble distance of PGC 1311290 and PGC 30058 (which see for images), they may merely happen to be in the same direction and at nearly the same distance; but given their peculiar appearance there is a good chance that they were involved in a relatively recent encounter, and their distorted appearance is a result of that encounter. With a relatively large difference in their radial velocities of 445 km/sec (presuming that they are actually at nearly the same distance would require the difference in their recessional velocities to be a real relative velocity), whether they will just pass each other the one time or their gravitational interaction will eventually cause them to merge is another matter entirely, and can only be the subject of speculation. (Note: PGC 1311290 is listed in NED as SDSS J101738.26+065834.9)

Historical Identification: As noted in the entry for NGC 3186 there is nothing near the NGC position for that object; but the CGCG listed a galaxy 6 arcmin south and 90 seconds of time west of the NGC position as a candidate for NGC 3186, and it has been accepted as such by the NED, albeit with a warning about the identification not being certain. As in the case of PGC 30058, for the usually precise Marth to make such an error in the position is almost inconceivable, and though Corwin (once again) reluctantly concedes the possibility, it is hard to justify the identification. But again, since the reader may run into this identification of NGC 3186 it feels necessary to discuss it here, even if only as a warning. (If there was any justification for Dreyer adding "several faint stars near" to Marth's description, then PGC 29963 might be a slightly better candidate for NGC 3186 than PGC 30085; but as noted in the entry for NGC 3186, the most probable identification for that object is "lost or nonexistent".)
Physical Information: Based on a recessional velocity of 8430 km/sec, a straightforward calculation indicates that PGC 29963 is 390 to 395 million light years away. 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 about 380 million light years away at the time the light by which we see it was emitted, about 385 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 0.5 by 0.5 arcmin, the galaxy is about 55 thousand light years across. PGC 29963 has a pair of fainter galaxies to its southwest, and although even if PGC 29963 really is NGC 3186 its "companions" are certainly too faint to be part of the NGC entry, the possibility that they might really be companions of the brighter galaxy led me to discuss them immediately below, and to label them in the closeup image for this entry.

Physical Information: Based on a recessional velocity of 8675 km/sec, a straightforward calculation indicates that PGC 1310913 is about 405 million light years away. 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 about 390 million light years away at the time the light by which we see it was emitted, about 395 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 0.2 by 0.15 arcmin, the galaxy is 20 to 25 thousand light years across. Given the small difference in their recessional velocities and Hubble distances, it may well be a physical companion of PGC 29963, which see for images. (Note: Listed in NED as SDSS J101552.57+065733.0)

Physical Information: The apparent size of J101552.6+065726 is about 0.4 by 0.05 arcmin. It is almost certainly a foreground object superimposed on PGC 1310913 (see PGC 29963 for images). It does not appear to be listed in any catalog, so nothing else is available, and whether it is near its apparent companions or considerably closer is unknown.

Historical Identification: Per Dreyer, NGC 3187 (= GC 2055, 3rd Lord Rosse, 1860 RA 10 10 05, NPD 67 25.1) is "very faint, extended". The position precesses to RA 10 17 45.4, Dec +21 53 03, less than half an arcmin north of the western end of the central bar of the galaxy listed above, the description fits and there is nothing comparable nearby so the identification is certain.
Discovery Notes: Although Dreyer credits the report of the discovery to William Parsons, 3rd Earl of Rosse, he notes that many of Rosse's nebular discoveries were actually made by his assistants, George Stoney, Bindon Stoney and R. J. Mitchell.
Physical Information: Based on a recessional velocity of 1580 km/sec, NGC 3187 is 70 to 75 million light years away, in fair agreement with redshift-independent distance estimates of 85 to 150 million light years. However, as a member of Hickson Compact Group 44 it probably has a distance corresponding to the average recessional velocity of the group, which is about 1360 km/sec (in which case its peculiar velocity relative to the average radial velocity of the Group would be about 220 km/sec), which corresponds to a distance of 60 to 65 million light years. Given that and its apparent size of 3.2 by 1.2 arcmin, it is about 60 thousand light years across. NGC 3187 is used by the Arp Atlas (with NGC 3190 and 3193) as an example of a group of galaxies. It is also a member of Hickson Compact Group 44.

Historical Identification: Per Dreyer, NGC 3188 (= GC 2056 = JH 690 = WH III 910, 1860 RA 10 10 17, NPD 31 53.1) is "very faint, pretty large, mottled but not resolved". The position precesses to RA 10 19 38.5, Dec +57 24 58, only 0.7 arcmin southwest of the galaxy listed above, the description fits and there is nothing comparable nearby so the identification is certain.
Physical Information: Given their distorted appearance and nearly identical recessional velocities, NGC 3188 and PGC 30179 are almost certainly interacting, and therefore at the same distance. Therefore, their Hubble distance should be based on the average of their recessional velocities (7800 km/sec for NGC 3188 and 7895 km/sec for PGC 30179). Based on a recessional velocity of 7850 km/sec, a straightforward calculation indicates that the pair is about 365 million light years away (NGC 3188 also has a single redshift-independent distance estimate of 140 million light years, but that is almost certainly incorrect and ignored here). 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 about 355 million light years away at the time the light by which we see it was emitted, about 360 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 1.25 by 1.1 arcmin, NGC 3188 is about 130 thousand light years across. It is listed as a starburst galaxy.

Physical Information: As discussed in the entry for NGC 3188, the distance of the interacting pair of galaxies is about 355 million light years. Given that and its apparent size of 0.4 by 0.15 arcmin, PGC 30179 is about 40 thousand light years across.

Historical Identification: Per Dreyer, NGC 3189 (= GC 2057, 3rd Lord Rosse, d'Arrest, 1860 RA 10 10 18, NPD 67 28) is "very very faint, much extended, parallel to h692", the last note indicating that it is on the same parallel of declination as NGC 3190. The position precesses to RA 10 18 02.3, Dec +21 50 08, right on the western end of the southwestern side of NGC 3190 (which see for images), and there is no doubt that NGC 3189 is simply part of NGC 3190. That galaxy is nearly edge-on and "split" by a prominent dust lane into a brighter northeastern side and a fainter southwestern side, making it look very much like two parallel nebulae.
Discovery Notes: Although Dreyer credits the report of the discovery to William Parsons, 3rd Earl of Rosse, he notes that many of Rosse's nebular discoveries were actually made by his assistants, George Stoney, Bindon Stoney and R. J. Mitchell.
Physical Information: Since NGC 3189 is merely part of NGC 3190, see that entry for anything else. The NGC entry is listed in LEDA as a galaxy part with the designation PGC 3518630, but a search of the database for that designation returns no results.

Historical Identification: Per Dreyer, NGC 3190 (= GC 2058 = JH 692 = WH II 44, 1860 RA 10 10 22, NPD 67 28.2) is "bright, pretty small, extended, pretty suddenly bright middle and nucleus". The position precesses to RA 10 18 06.2, Dec +21 49 55, almost dead center on the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Physical Information: Based on a recessional velocity of 1270 km/sec, NGC 3190 is about 60 million light years away, in good agreement with redshift-independent distance estimates of 60 to 100 million light years. However, as a member of Hickson Compact Group 44 it probably has a distance corresponding to the average recessional velocity of the group, which is about 1360 km/sec (in which case its peculiar velocity relative to the average radial velocity of the Group would be about 90 km/sec), which corresponds to a distance of 60 to 65 million light years. Given that and its apparent size of 4.2 by 1.2 arcmin, it is 75 to 80 thousand light years across. NGC 3190 is used by the Arp Atlas (with NGC 3187 and 3193) as an example of a group of galaxies. It is also a member of Hickson Compact Group 44.

Historical Identification: Per Dreyer, NGC 3191 (= GC 2059 = JH 691, 1860 RA 10 10 26, NPD 42 51.8) is "faint, small, round, brighter middle". The position precesses to RA 10 19 04.5, Dec +46 26 17, only an arcmin nearly due south of the galaxy listed above, the description fits and there is nothing comparable nearby so the identification is certain (see NGC 3192 for a discussion of the probable duplicate entry).
Physical Information: Based on a recessional velocity of 9210 km/sec, a straightforward calculation indicates that NGC 3191 is about 430 million light years away. 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 410 to 415 million light years away at the time the light by which we see it was emitted, about 420 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 0.95 by 0.85 arcmin, it is about 115 thousand light years across. The galaxy to its west (PGC 30128) may be a physical companion (and perhaps even the cause of its distorted appearance), so though definitely not part of the NGC entry it is discussed immediately below.

Physical Information: Based on a recessional velocity of 8985 km/sec, a straightforward calculation indicates that PGC 30128 is 415 to 420 million light years away. 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 about 405 million light years away at the time the light by which we see it was emitted, about 410 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 0.35 by 0.25 arcmin, the galaxy is about 40 thousand light years across. (Although these calculations assume that the difference in radial velocity between PGC 30128 and NGC 3191 indicates a difference in distance of up to 10 million light years, it is also possible that they are physical companions (if at exactly the same distance from us they would be only about 150 thousand light years apart) and their distorted appearance may therefore be due to some kind of interaction between them; hence my decision to place this entry here instead of on the appropriate PGC page.)

Historical Identification: Per Dreyer, NGC 3192 (= GC 2060 = WH III 704, 1860 RA 10 10 28, NPD 42 43.7) is "extremely faint, very small (perhaps = h691?)", the last remark indicating that Dreyer suspected that NGC 3192 might be a duplication of NGC 3191 (John Herschel's GC had already indicated some uncertainty about his father's II 704, but not in such certain terms). The position precesses to RA 10 19 06.9, Dec +46 34 22, about 7 arcmin nearly due north of the galaxy listed above, but there is nothing else within a much larger region that the elder Herschel could have seen, so unless he mistook a star for a nebula (in which case whatever he saw would be irretrievably lost) he must have seen the same object as his son, so the duplicate entry is usually considered certain. (Corwin states "WH's NPD is -9 arcmin in error, close enough to 10 to make this pretty clearly a digit mistake in reduction or copying", the idea being that the error is similar to those encountered in balancing checkbooks when one entry is off by a single digit.)
Discovery Notes: Herschel's comparison star was 60 UMa, which has a position of J2000 RA 11 38 33.5, Dec +46 50 03. Its proper motion is -0.035"/yr in RA and -0.0272"/yr in Dec, meaning that in the 212 years since Herschel's observation it moved 0.5 seconds west and 6 arcsec south of its position in 1788, making its position at that time J2000 RA 11 38 34.0, Dec +46 50 09 = (1788) RA 11 27 06.1, Dec +48 00 29. Adding Herschel's offsets of 81m 11s west and 22 arcmin south for (WH) II 704, that object should have been at (1788) RA 10 05 55.1, Dec +47 38 29, which corresponds to J2000 RA 10 19 04.4, Dec +46 35 18 (whence the position for a possibly lost or nonexistent object above), about an arcmin north of the NGC position, and about 8 arcmin north of NGC 3191, thereby closely corresponding to Corwin's comment.
Physical Information: Given the generally accepted duplication, see NGC 3191 for anything else.

Historical Identification: Per Dreyer, NGC 3193 (= GC 2061 = JH 693 = WH II 45, 1860 RA 10 10 41, NPD 67 24.4) is "bright, small, very little extended, pretty suddenly a little brighter middle, 9.5 magnitude star 80 arcsec away at position angle 354°". The position precesses to RA 10 18 25.2, Dec +21 53 42, right on the galaxy listed above, the description is a perfect fit and there is nothing comparable nearby so the identification is certain.
Physical Information: Based on a recessional velocity of 1380 km/sec, NGC 3193 is about 65 million light years away, in good agreement with redshift-independent distance estimates of 50 to 125 million light years. However, as a member of Hickson Compact Group 44 it probably has a distance corresponding to the average recessional velocity of the group, which is about 1360 km/sec (in which case its peculiar velocity relative to the average radial velocity of the Group would be about 20 km/sec), which corresponds to a distance of 60 to 65 million light years. Given that and its apparent size of 3.1 by 2.6 arcmin, it is about 55 thousand light years across. NCG 3193 is used by the de Vaucouleurs Atlas of Galaxy Types as an example of galaxy type E2. It is also used by the Arp Atlas (with NGC 3187 and 3190) as an example of a group of galaxies. It is also a member of Hickson Compact Group 44.

Historical Identification: Per Dreyer, NGC 3194 (= GC 2062 = WH III 965, 1860 RA 10 10 47, NPD 14 29.7) is "very faint, very small [Place very questionable]". The position precesses to RA 10 23 04.1, Dec +74 48 11, in a completely stellar field. However, although Dreyer made no comment about GC 2062 in his 1877 Supplement to the General Catalog, by the time he compiled the NGC he was aware of the fact that all of Herschel's observations of Apr 2, 1801 suffered from some large, inexplicable error (hence "Place very questionable"). As discussed here, that led him to request (in the early 1900's) that the Astronomer Royal take photographic plates of the region observed by Herschel on that night, and as a result Dreyer's 1912 revision of the NGC included the notes "3155 is = (WH) III 965", and "3194 to be struck out (= 3155)", so the correct identification (and duplicate entry) has been known for more than a century.
Discovery Notes: Although Dreyer was able to identify what Herschel observed, it was not until 2011-12 that Wolfgang Steinicke showed that the problem was due to the observations of the date in question having been made with the telescope 7 degrees out of alignment with the meridian, causing reductions of the measurements based on the assumption that it was aligned with the meridian to be badly askew (as discussed in the note mentioned above).
Physical Information: Given the duplicate entry, see NGC 3155 for anything else.

Historical Identification: Per Dreyer, NGC 3195 (= GC 2063 = JH 3241, 1860 RA 10 10 52, NPD 170 10.2) is "a remarkable object, a planetary nebula, pretty bright, small, a little extended, 13 arcsec diameter, 3 small (faint) stars near". The position precesses to RA 10 09 25.6, Dec -80 51 43, on the southeastern rim of the planetary nebula listed above, the description fits (save for the fact that the nebula is much larger than a visual observation would suggest) and there is nothing comparable nearby so the identification is certain.
PGC Designation Note: For purposes of completeness LEDA assigned a PGC designation to this object, even though it is not a galaxy; but a search of the database for that designation returns no result, so it is shown in quotes.
Physical Information: NGC 3195 is thought to be about 5500 light years away. Given that and its apparent size of about 45 by 37 arcsec, it is about 1.2 light years across. The white dwarf at its center is about magnitude 15.5. The nebula is approaching us (or we are approaching it) at about 17 km/sec, and it is expanding at about 40 km/sec; but its original speed of expansion must have been hundreds of times faster than that. (Note: Most images of the nebula, including the one in the Hubble Gallery of Planetary Nebulae, have east and west reversed; the images below show north at the top and east on the left, as is typical for images on this site unless otherwise specified.)

Historical Identification: Per Dreyer, NGC 3196 (= GC 2064 = JH 694 = III 348, 1860 RA 10 10 54, NPD 61 38.5) is "most extremely faint, pretty small, a little extended". The position precesses to RA 10 18 48.3, Dec +27 39 34, less than 0.6 arcmin south southwest of the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Physical Information: Based on a recessional velocity of 15105 km/sec, a straightforward calculation indicates that NGC 3196 is 700 to 705 million light years away. 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 660 to 665 million light years away at the time the light by which we see it was emitted, about 680 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 0.4 by 0.15 arcmin, the galaxy is about 75 to 80 thousand light years across.

Historical Identification: Per Dreyer, NGC 3197 (= GC 2065 = WH III 966, 1860 RA 10 10 58, NPD 11 04.9) is "very faint, very small [Place very questionable]". The position precesses to RA 10 24 47.0, Dec +78 12 54, but there is nothing there that Herschel could have seen. However, although Dreyer made no comment about GC 2065 in his 1877 Supplement to the General Catalog, by the time he compiled the NGC he was aware of the fact that all of Herschel's observations of Apr 2, 1801 suffered from some large, inexplicable error (hence "Place very questionable"). As discussed here, that led him to request (in the early 1900's) that the Astronomer Royal take photographic plates of the region observed by Herschel on that night, and as a result Dreyer's 1912 revision of the NGC included the note "3197. (WH) III 966. Greenwich place is RA 10 00 16, NPD 11 29.6", which precesses to RA 10 14 27.5, Dec +77 49 10, right on the galaxy listed above, so the correct identification has been known for more than a century.
Discovery Notes: Although Dreyer was able to identify what Herschel observed, it was not until 2011-12 that Wolfgang Steinicke showed that the problem was due to the observations of the date in question having been made with the telescope 7 degrees out of alignment with the meridian, causing reductions of the measurements based on the assumption that it was aligned with the meridian to be badly askew (as discussed in the note mentioned above).
Physical Information: Based on a recessional velocity of 8085 km/sec, a straightforward calculation indicates that NGC 3197 is about 375 million light years away, in fair agreement with redshift-independent distance estimates of 340 to 360 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 about 365 million light years away at the time the light by which we see it was emitted, about 370 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 1.2 by 0.85 arcmin, the galaxy is 125 to 130 thousand light years across. The galaxy's unusually bright nucleus suggests that it may be a starburst galaxy.

Historical Identification: Per Dreyer, NGC 3198 (= GC 2066 = JH 695 = WH I 199, 1860 RA 10 11 14, NPD 43 44.3) is "pretty bright, very large, much extended 45°, very gradually brighter middle". The position precesses to RA 10 19 49.3, Dec +45 33 42, just off the northwestern rim of the galaxy listed above, the description fits and there is nothing else nearby so the identification is certain.
Physical Information: Based on a recessional velocity of 660 km/sec, NGC 3198 is about 30 million light years away, in reasonable agreement with redshift-independent distance estimates of 30 to 55 million light years. Given that and its apparent size of 9.0 by 3.7 arcmin (counting most of its fainter outer extensions), it is 75 to 80 thousand light years across.

Historical Identification: Per Dreyer, NGC 3199 (= GC 2067 = JH 3239, (Dunlop 332), 1860 RA 10 11 46, NPD 147 15.7) is "a remarkable object, very bright, very large, falcate, double star involved" (falcate means curved like a sickle). The second IC adds "No nebula on photos at Arequipa (Harv. Ann., xxvi. 207). h. observed it 4 times. Has it disappeared?" The position precesses to RA 10 16 44.9, Dec -57 57 35, right on the brightest part of the sickle-shaped arc which is all that Dunlop or Herschel could have observed, so the identification is certain. However, NGC 3199 is now often thought of as the more or less round (but mostly far fainter) nebula to the east of the sickle, hence the difference between Herschel's position and the one listed above, which is close to the center of the circular region (and is used as the center of the wide-field image below).
Discovery Notes: Per Corwin, Dunlop had a South Polar Distance a degree too large, putting his #332 a degree north of its correct position, so Herschel couldn't find anything at Dunlop's position. When he did observe the nebula he used a North Polar Distance for his calculations, reducing the chance of noticing the similarity of the two positions, so his independent discovery appeared to be the only observation of the nebula at the time Dreyer compiled the NGC (and as noted above, there were some puzzlingly futile efforts to find it again). The equivalence between Dunlop and Herschel's observations is a relatively recent discovery, and therefore not generally known even now.
Physical Information: NGC 3199 is about 12000 light years away. Given that and its apparent size of about 20 by 15 arcmin, its roughly circular outline is about 75 light years across. Its nonuniform brightness appears to be due to an uneven distribution of clouds of gas surrounding the Wolf-Rayet star near the center of the nebula; where those clouds are denser they glow brighter, forming the curved arc that is technically NGC 3199. Listed in LEDA as a nebula with designation PGC 3517658, but a search of the database for that designation returns no result.