Historical Identification: Per Dreyer, NGC 6000 (= GC 4142 = JH 3614, 1860 RA 15 41 11, NPD 118 57.3) is "very faint, small, round, suddenly brighter middle".
Physical Information: Apparent size 1.9 by 1.6? arcmin

Historical Identification: Per Dreyer, NGC 6001 (= GC 4143 = WH III 371, 1860 RA 15 42 04, NPD 60 54.9) is "very faint, small, round".
Physical Information: Apparent size 1.2 by 1.1 arcmin (as measured from the images below).

Historical Identification: Per Dreyer, NGC 6002 (= GC 5788, 4th Lord Rosse, 1860 RA 15 42 04, NPD 60 56.6) is a "nebula 100 arcsec south of III 371", (WH) III 371 being NGC 6001. The position precesses to RA 15 47 48.6, Dec +28 37 24, but there is nothing there. However, the NGC position contains round-off errors that put it nearly an arcmin northeast of Lord Rosse's position (which was nearly 100 arcsec south of NGC 6001, as stated in Dreyer's description, or more accurately, 97.6 arcsec from that galaxy, at a position angle of 197.3 degrees). There is nothing of note there either, but the faint star listed above lies less than 0.35 arcmin beyond Lord Rosse's position, could certainly have been seen with his 72-inch Leviathan, and is generally considered the best candidate for what Rosse observed. However, several references list the galaxy (PGC 56051) about an arcmin southwest of NGC 6001 as NGC 6002. That is certainly wrong, because both the distance and direction are completely at odds with Lord Rosse's measurements, and such a faint galaxy would almost certainly have been beyond the reach of even his telescope (keeping in mind the fact that in modern photographs extended objects such as galaxies can look as bright or brighter than equally bright stars, but for visual observers stars look much brighter than nebulae, because the extended objects' light, being spread out over a wider area, is too faint for the eye to notice). However, given its frequent misidentification as NGC 6002, PGC 56051 is discussed in the next entry.

Above, a 6 arcmin wide SDSS image centered on the star that is probably NGC 6002. Lord Rosse's position is shown by a plus sign just northeast of the star (just above the GC in NGC 6002), the "rounded-off" NGC position by a plus sign in a box, and PGC 56051 is identified by its PGC designation.

Historical Identification: See NGC 6002 for a discussion of why PGC 56051 cannot be that NGC object.
Physical Information: Based on a recessional velocity of 9980 km/sec, a straightforward calculation indicates that PGC 56051 is about 465 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 445 million light-years away at the time the light by which we see it was emitted, about 455 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 0.45 by 0.1 arcmin, the galaxy is about 60 thousand light-years across.

Historical Identification: Per Dreyer, NGC 6003 (Stephan list X (#28), 1860 RA 15 43 10, NPD 70 32.2) is "faint, very small, small star involved".
Physical Information: Apparent size 0.9 by 0.8? arcmin

Historical Identification: Per Dreyer, NGC 6004 (Stephan list X (#29), 1860 RA 15 44 07, NPD 70 38.1) is "very faint, pretty large, a little extended, a little brighter middle".
Physical Information: Apparent size 1.8 by 1.7? arcmin

Historical Identification: Per Dreyer, NGC 6005 (= GC 4144 = JH 3615, Dunlop 334, 1860 RA 15 44 35, NPD 147 01.0) is a "cluster, pretty small, pretty rich, much compressed, stars of 16th magnitude".
Physical Information: Apparent size 5.0? arcmin

Historical Identification: Per Dreyer, NGC 6006 (= GC 5789, Marth #294, 1860 RA 15 46 27, NPD 77 35) is "very faint, small".
Physical Information: Apparent size 0.6 by 0.4? arcmin

Historical Identification: Per Dreyer, NGC 6007 (= GC 5790, Marth #295, 1860 RA 15 46 46, NPD 77 38) is "faint, pretty large".
Physical Information: Apparent size 1.7 by 1.2? arcmin

Historical Identification: Per Dreyer, NGC 6008 (Stephan list XI (#19), 1860 RA 15 56 48, NPD 68 28.8) is "very faint, round, pretty large, brighter middle". The position precesses to RA 15 52 56.8, Dec +21 06 03, within the outline of the galaxy, so the identification is certain.
Physical Information: Based on a recessional velocity of 4870 km/sec, NGC 6008 is about 225? million light-years away. Given that and its 1.4 by 1.3? arcmin apparent size, it is about 90 thousand light-years across. Based on their similar distance and direction, NGC 6008 and PGC 56301 may be a physical pair (their difference in radial velocity is less than normal peculiar (non-Hubble expansion) velocities, so the difference in their estimated distances may be real, or illusory).

Physical Information: Based on a recessional velocity of 5120 km/sec, PGC 56301 is about 240 million light-years away. Given that and its 0.7 by 0.5 arcmin apparent size, it is about 50 thousand light-years across. Based on their similar distance and direction, PGC 56301 and NGC 6008 may be a physical pair (their difference in radial velocity is less than normal peculiar (non-Hubble expansion) velocities, so the apparent difference in distance may be real, or illusory).

Historical Identification: Per Dreyer, NGC 6009 (= GC 5791, Marth #296, 1860 RA 15 46 48, NPD 77 31) is "faint, very small, stellar".
Physical Information: Apparent size 0.5 by 0.2? arcmin

Historical Identification: Per Dreyer, NGC 6010 (= GC 4145 = JH 1939 = WH II 583, 1860 RA 15 47 10, NPD 89 02.3) is "pretty faint, small, extended 90 , gradually brighter middle, mottled but not resolved".
Physical Information: Apparent size 2.0 by 0.5? arcmin

Historical Identification: Per Dreyer, NGC 6011 (= GC 4146 = WH III 313, 1860 RA 15 47 36, NPD 17 24.9) is "very faint, small, extended 90 , very small star to east".
Physical Information: Apparent size 2.0 by 0.7? arcmin

Historical Identification: Per Dreyer, NGC 6012 (= GC 4147 = WH II 657, 1860 RA 15 47 49, NPD 75 00.0) is "faint, between 2 bright stars".
Physical Information: Apparent size 2.1 by 1.5? arcmin

Historical Identification: Per Dreyer, NGC 6013 (= GC 5792, Stephan list VII (#1), 1860 RA 15 47 59, NPD 48 56.3) is "extremely faint, very small, irregularly round, a little brighter middle".
Physical Information: Apparent size 1.4 by 0.8? arcmin

Historical Identification: Per Dreyer, NGC 6014 (= GC 4148 = JH 1940, 1860 RA 15 49 04, NPD 83 39.5) is "pretty bright, pretty large, extended".
Physical Information: Based on a recessional velocity of 2490 km/sec, NGC 6014 is about 115 million light-years distant. Given that and its apparent size of 1.7 by 1.6 arcmins, it is about 55 thousand light-years across.

Historical Identification: Per Dreyer, NGC 6015 (= GC 4149 = WH III 739, 1860 RA 15 49 23, NPD 27 16.0) is "very faint, pretty large, round, very gradually brighter middle (d'Arrest: bright, much extended)". The first IC adds "d'Arrest's description is correct (Denning)".
Discovery Notes: In a paper of Apr 13, 1891 Denning discusses the variability of nebulae as described by different observers or at different times and ascribes it to differences in the quality of the sky, nebulae appearing brighter on better nights and appearing fainter on poorer ones. Among others, he gives as an example the difference between Herschel's description of NGC 6015 as very faint, and d'Arrest's calling it bright. This is presumably the source of Dreyer's statement in the IC1, but does not necessarily mean that Denning actually observed NGC 6015 and confirmed that d'Arrest was correct, nor indicate when he observed it, if he did. It seems reasonable to suppose that his use of that example was based on an observation that confirmed d'Arrest's description, or why would he use it, instead of another? But though, probably on that basis, Dreyer mentioned Denning's note, I have only listed Denning's supposed observation as "probable".
Physical Information: Apparent size 5.4 by 2.1? arcmin

Historical Identification: Per Dreyer, NGC 6016 (= GC 5793, Marth #297, 1860 RA 15 50 04, NPD 62 38) is "very faint, small, extended".
Physical Information: Apparent size 1.0 by 0.5? arcmin

Historical Identification: Per Dreyer, NGC 6017 (= GC 4150 = JH 1941, 1860 RA 15 50 22, NPD 83 35.7) is "a remarkable object, very faint, very small, round, disc gradually then suddenly much brighter middle".
Physical Information: Apparent size 0.8 by 0.7? arcmin

Historical Identification: Per Dreyer, NGC 6018 (= GC 4151 = JH 1942 = WH III 646, 1860 RA 15 51 05, NPD 73 42.7) is "very faint, small, a little extended, western of 2", the other being NGC 6021.
Physical Information: Apparent size 1.4 by 0.7? arcmin

Historical Identification: Per Dreyer, NGC 6019 (Swift list IV (#18), 1860 RA 15 51 05, NPD 24 43.7) is "most extremely faint, small, round, very difficult".
Physical Information: Apparent size 0.4 by 0.4? arcmin

Historical Identification: Per Dreyer, NGC 6020 (= GC 5794, Stephan list VII (#??), (Safford #10), 1860 RA 15 51 05, NPD 67 11.2) is "extremely faint, extremely small, irregularly round, a little brighter middle".
Discovery Notes: An odd duplication caused by Dreyer not noticing Safford's observations until after finishing the NGC. As a result, the original entry for NGC 6020 lists another observer and different data; but there is no doubt that Safford's observation was of the same object at an earlier date, hence his being credited with a double discovery on the basis of a single observation.
Physical Information: Apparent size 1.4 by 1.0? arcmin.

Historical Identification: Per Dreyer, NGC 6021 (= GC 4152 = JH 1943 = WH III 73, 1860 RA 15 51 07, NPD 73 37.7) is "extremely faint, very small, a little extended, eastern of 2", the other being NGC 6018.
Physical Information: Apparent size 1.4 by 0.8? arcmin

Historical Identification: Per Dreyer, NGC 6022 (Stephan list XII (#76), 1860 RA 15 51 25, NPD 73 18.7) is "extremely faint, extremely small".
Physical Information: Apparent size 0.7 by 0.5? arcmin

Historical Identification: Per Dreyer, NGC 6023 (Stephan list XII (#77), 1860 RA 15 51 28, NPD 73 17.0) is "faint, small, round, brighter middle".
Physical Information: Apparent size 1.4 by 1.0? arcmin

Historical Identification: Per Dreyer, NGC 6024 (Swift list IV (#19), 1860 RA 15 51 50, NPD 24 40.0) is "pretty faint, pretty small, round, brighter middle, star close".
Physical Information: Apparent size 0.7 by 0.6? arcmin

Historical Identification: Per Dreyer, NGC 6025 (= GC 4153 = JH 3616, Lacaille III 10, Dunlop 304, 1860 RA 15 51 51, NPD 150 06.0) is a "cluster, bright, very large, pretty rich, a little compressed, stars from 7th magnitude".
Physical Information: Apparent size 15? arcmin

Historical Identification: Per Dreyer, NGC 6026 (= GC 4154 = JH 3617, 1860 RA 15 52 19, NPD 124 08.6) is "faint, small, round, gradually pretty much brighter middle, triangle of stars to northwest".
PGC Designation Note: For purposes of completeness, LEDA assigned a PGC designation to this object, even though it isn't a galaxy; but a search of the database for that designation returns no result, so it is shown in quotes.
Physical Information: As is usual for such nebulae, the central star is a white dwarf; but in this case it is also a close binary, with a red giant companion. As a result of the orbital motion of the pair, the system varies in brightness over a period of 0.528 days, which would normally correspond to an identical orbital period; but spectroscopic studies show that the actual orbital period is twice as long. The difference is interpreted as being due to the larger star having expanded until it fills its Roche lobe (the point at which any further expansion would result in material being torn away by the other star), and as a result, having an ellipsoidal shape which alters the brightness of the system according to how the ellipsoid is turned relative to our line of sight. The apparent size of the nebula is 0.9 by 0.6 arcmin; apparently nothing else is available.

Historical Identification: Per Dreyer, NGC 6027 (Stephan list XII (#78), 1860 RA 15 53 03, NPD 68 49.8) is "extremely faint, very faint star involved, 2 very faint stars near". The position precesses to RA 15 59 11.8, Dec +20 46 08, only half an arcmin north of the center of the group listed above and a third of an arcmin from the northernmost member, the description fits and there is nothing else nearby, so the identification is certain. Stephan obviously could not see the individual components of the group, but only the overall light of the entire assemblage; so NGC 6027 is considered to comprise the entire grouping. This entry covers the group as a whole, while the following six entries discuss the individual members of the group.
Note About The Small Letters Used Here: In the labeled image below and the discussion of individual galaxies which follow this listing, the labels correspond to those used by Seyfert; but various references use different listings, so "A" or "B" in one list may not correspond to "A" or "B" in another, and in fact often does not. As a result, alternative listings such as their PGC designations are the usual way to be sure which galaxy is being discussed, and it is quite possible that the confusion in NED with even those designations (as noted in the individual entries below) may mean that data assigned to one member of the Sextet may have actually been meant for another member.
Physical Information: NGC 6027, or "Seyfert's Sextet", is a compact group of four galaxies, a part torn from one of them as a result of their gravitational interaction, and a background galaxy. When noted by Carl Seyfert in 1951, it was the most compact group of galaxies discovered to date. The individual galaxies range from 25 to 50 thousand light-years across, and the whole group occupies a region only about the size of our Milky Way galaxy. The four interacting galaxies and their distorted extensions have recessional velocities ranging from 4000 to 4570 km/sec (the "peculiar velocities" of the galaxies, meaning the difference between their average recessional velocity and their individual velocities, represent actual radial motions of the galaxies relative to each other). Based on an average recessional velocity of about 4255 km/sec (and H₀ = 70 km/sec/Mpc), the group's distance is about 195 to 200 million light-years, in reasonable agreement with widely varying redshift-independent distance estimates of about 155 to 325 million light-years. The background galaxy (NGC 6027d in the listing below) has a recessional velocity of 19815 km/sec, which corresponds to a distance of about 855 million light-years (see its separate listing for more about that). It is believed that over a period of several billion years, the interacting members of NGC 6027 will collide with each other over and over, until they finally merge into a single galaxy.

NED Designation: UGC 10116 NED01 (mis-listed as PGC 56575)
Physical Information: Based on a recessional velocity of 4395 km/sec (and H₀ = 70 km/sec/Mpc), PGC 56579 should be about 205 million light-years. However, based on its obvious interaction with its companions, it must share their common distance of about 195 to 200 million light-years. Given that and its apparent size of about 0.5 by 0.2 arcmin (from the HST image), it is about 25 to 30 thousand light-years across.

NED Designation: UGC 10116 NED02
Physical Information: Based on a recessional velocity of 4250 km/sec (and H₀ = 70 km/sec/Mpc), PGC 56576 should be about 195 to 200 million light-years away (which agrees with the distance based on the average motion of the galaxies in the group). Given that and its apparent size of about 0.55 by 0.4 arcmin (from the HST image), it is about 30 to 35 thousand light-years across.

NED Designation: UGC 10116 NED03 (mis-listed as PGC 56584 in NED)
Physical Information: Based on a recessional velocity of 4055 km/sec (and H₀ = 70 km/sec/Mpc), PGC 56575 should be about 185 to 190 million light-years away. However, based on its obvious interaction with its companions, it must share their common distance of about 195 to 200 million light-years. Given that and its apparent size of about 0.4 by 0.2 arcmin (from the HST image), it is about 20 to 25 thousand light-years across.

NED Designation: UGC 10116 NED04
Physical Information: Based on a recessional velocity of 4570 km/sec (and H₀ = 70 km/sec/Mpc), PGC 56578 should be about 215 million light-years away. However, based on its obvious interaction with its companions, it must share their common distance of about 195 to 200 million light-years. Given that and its apparent size of about 0.8 by 0.25 arcmin (from the HST image), it is about 45 thousand light-years across.

NED Designation: UGC 10116 NED05
Physical Information: Based on a recessional velocity of 19815 km/sec (and H₀ = 70 km/sec/Mpc), a straightforward calculation indicates a distance for NGC 6027d of about 920 to 925 million light-years. However, for objects at that distance, we must take into account the expansion of the Universe during the time it took the galaxy's light to reach us. Doing that shows that NGC 6027d was about 855 million light-years away when the light by which we see it was emitted, about 880 to 885 million years ago (the difference between the two numbers being due to the expansion of the intervening space during that interval). Given that and its apparent size of about 0.35 by 0.25 arcmin (from the HST image), NGC 6027d is about 85 to 90 thousand light-years across. Unlike the other members of Seyfert's Sextet, NGC 6027d is not a member of the compact group of interacting galaxies; instead, as indicated by its estimated distance, it is a background galaxy over four times more distant than its apparent companions.

NED Designation: UGC 10116 NED06 (mis-listed as HCG 79f and PGC 56579 in NED)
Physical Information: Based on a recessional velocity of 4000 km/sec (and H₀ = 70 km/sec/Mpc), PGC 56584 should be about 185 to 190 million light-years away. However, based on its obvious interaction with its companions, it must share their common distance of about 195 to 200 million light-years. Given that and its apparent size of about 0.65 by 0.3 arcmin (from the HST image), it is about 35 to 40 thousand light-years across. It may not be a separate galaxy but simply a part of PGC 56579 that was torn away by a recent collision or gravitational interaction with its companions.

Historical Identification: Per Dreyer, NGC 6028 (Bigourdan (list II #76), 1860 RA 15 55 20, NPD 70 14) is "very faint, pretty small, no nucleus".
Physical Information: Apparent size 1.3 by 1.1? arcmin

Historical Identification: Per Dreyer, NGC 6029 (= GC 5795, Marth #298, 1860 RA 15 55 24, NPD 77 01) is "very faint, very small".
Physical Information: Apparent size 1.2 by 0.7? arcmin

Historical Identification: Per Dreyer, NGC 6030 (Stephan list XIII (#84), 1860 RA 15 55 35, NPD 71 39.0) is "pretty faint, very small, round, brighter middle".
Physical Information: Apparent size 1.2 by 0.8? arcmin

Historical Identification: Per Dreyer, NGC 6031 (= GC 4155 = JH 3618, Dunlop 359, 1860 RA 15 56 43, NPD 143 38.5) is a "cluster, small, much compressed, stars from 11th to 14th magnitude".
Physical Information: Apparent size 3.0? arcmin

Historical Identification: Per Dreyer, NGC 6032 (Stephan list XI (11c#1), 1860 RA 15 56 54, NPD 68 39.1) is "very faint, pretty large, a little extended, very little brighter middle, northwestern of 2", the other being NGC 6035.
Physical Information: Apparent size 1.6 by 0.7? arcmin.

Historical Identification: Per Dreyer, NGC 6033 (= GC 5796, Marth #299, 1860 RA 15 57 09, NPD 91 44) is a "very faint nebulous star".
Physical Information: Apparent size 1.1 by 1.0? arcmin

Historical Identification: Per Dreyer, NGC 6034 (Swift list IV (#20), 1860 RA 15 57 10, NPD 72 23.3) is "most extremely faint, very small, round, very difficult".
Physical Information: Apparent size 1.0 by 0.8? arcmin

Historical Identification: Per Dreyer, NGC 6035 (Stephan list XI (11c#2), 1860 RA 15 57 17, NPD 68 43.1) is "very faint, pretty large, a little extended, southeastern of 2", the other being NGC 6032.
Physical Information: Apparent size 0.9 by 0.9? arcmin.

Historical Identification: Per Dreyer, NGC 6036 (= GC 5797, Marth #300, 1860 RA 15 57 31, NPD 85 45) is "very faint, very small, round, stellar".
Physical Information: Apparent size 1.1 by 0.4? arcmin

Historical Identification: Per Dreyer, NGC 6037 (= GC 5798, Marth #301, 1860 RA 15 57 32, NPD 85 49) is "very faint, small".
Physical Information: Apparent size 0.7 by 0.6? arcmin

Historical Identification: Per Dreyer, NGC 6038 (= GC 4156 = JH 1944 = WH III 622, 1860 RA 15 57 35, NPD 52 15.6) is "very faint, small, round, 10th magnitude star to southeast".
Physical Information: Apparent size 1.1 by 1.1? arcmin

Historical Identification: Per Dreyer, NGC 6039 (Swift list IV (#21), 1860 RA 15 58 08, NPD 71 55.2) is "most extremely faint, very small, round, south-preceding (southwestern) of 3 in line," the others being NGC 6040 and 6041 (though the direction is wrong, as discussed in the Discovery Note below). The position precesses to RA 16 04 25.8, Dec +17 41 39, about 3.3 arcmin nearly due west of the galaxy listed above, and with several other galaxies in the region, the identification would normally be uncertain (and in fact the galaxy nearly 3 arcmin nearly due north of Swift's position is often misidentified as NGC 6039, leading to some serious problems with modern catalogs, as part of this entry discusses).
Solution To The Identification: Swift's original paper says "south-preceding (southwestern) of 3 in a line; the other 2 being 2 of Stephan's; 3rd of 10". But this object could only be the 3rd of 10 if it is the galaxy to the southeast of NGC 6040 and 6041 (namely NGC 6042), and Swift's statement that it was the 3rd of 10 means he knew it was to the east of Stephan's objects, so he must have meant to say that it was the southeastern of 3 (in fact the copy of his paper that I downloaded has a handwritten correction to "south-following"), and that and the fact that Swift's declinations (in the NGC, converted to North Polar Distances) were usually far more accurate than his right ascensions means that his object was almost certainly the galaxy to the east of his position, and not the one to the north of it. As noted in the entry for NGC 6042, because of the error in Swift's right ascension, when Stephan observed the region he presumed that he had discovered a new object, which led to the duplicate entry; and although Stephan's position was far better, tradition almost always leads to a duplicate entry being called by its smaller numerical value, so since NGC 6039 is almost certainly a duplicate observation of NGC 6042, the galaxy is almost always called NGC 6039, and its identification as the galaxy listed above is considered adequately certain.
Supposed Use By The Arp Atlas: The Arp Atlas of Peculiar Galaxies lists the pair of galaxies that comprise Arp 122 as NGC 6039, presumably because of an incorrect identification of NGC 6039 as the galaxy to the north of Swift's position (the same misidentification was used by Vorontsov-Velyaminov), and the Atlas includes an image of what is supposedly that galaxy and NGC 6040 labeled as Arp 122, along with a note stating that they are part of the Hercules Cluster of galaxies. The pair is used by the Atlas as one of several examples of an elliptical galaxy (supposedly NGC 6039) close to and perturbing a spiral galaxy (NGC 6040). However, the pair identified by Arp as NGC 6039 is not NGC 6039, but NGC 6040 and PGC 56942 (which is often called NGC 6040B, a non-standard designation that should never be used for any purpose except to warn against such non-standard designations), so NGC 6039/42 is not part of any Arp object.
Note About Designation Error: A search of HyperLEDA for NGC 6039/42 shows the correct galaxy and correct data, but a search of NED shows PGC 56942, but with the correct data for the NGC 6039(!) This is unusual, as an error in the identification almost always also involves an error in the information shown for the object.
Physical Information: Based on a recessional velocity relative to the Cosmic Background Radiation of 10765 km/sec (and H₀ = 70 km/sec/Mpc), a straightforward calculation indicates that NGC 6039 is about 500 to 505 million light-years away, in good agreement with redshift-independent distance estimates of about 425 to 550 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 over 480 million light-years away at the time the light by which we see it was emitted, almost 490 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 0.8 by 0.75 arcmin (from the images below), the galaxy is about 110 thousand light-years across.
Use By The de Vaucouleurs Atlas: NGC 6039/6042 is used by the de Vaucouleurs Atlas of Galaxies as an example of galaxy type E⁺1 (gE), the "gE" standing for giant elliptical, while the "+" sign indicates that the galaxy would be classified as E/S0 in the earlier Hubble-Shapley classification scheme. LEDA and NED both use the E/S0 classification, and since that corresponds to the alternative de Vaucouleurs classification, I have used that (plus a "g" to indicate the galaxy's "giant" status) in the description line above. (Note: The "kudzu" image linked from my de Vaucouleurs page shows everything from NGC 6040 to 6042 without any labels; the central galaxy is NGC 6041, the one to is southeast is NGC 6042/39, and the pair to the northwest is the actual Arp 122.)

Historical Identification: Per Dreyer, NGC 6040 (= GC 5799, Stephan list I (#1), 1860 RA 15 58 09, NPD 71 51.9) is "very faint, extremely small, faint star close". The position precesses to RA 16 04 26.7, Dec +17 44 57, practically dead center on the galaxy listed above and the description fits (with the 'faint star close' perhaps being the galaxy to the south), so the identification is certain. The galaxy to the south, PGC 56942, is often misdesignated "NGC 6040B" or even misidentified as NGC 6039 (which see), and some references list NGC 6040 as a double galaxy; but since Stephan's position falls exactly on the more northerly galaxy it is unlikely that he thought whatever might lie to the south had anything to do with his nebula, and PGC 56942 is therefore not an NGC object (though it is part of Arp 122).
Misidentifications: NGC 6040 has been misidentified as NGC 6039 by Vorontsov-Velyaminov and Arp, and as href=ic11a.htm#ic1170>IC 1170 by NED. Its companion, PGC 46042, is also misidentified as NGC 6039 (primarily by NED), and UGC and CGCG both list the two galaxies as a single object; so there are enough mistakes to fill a small handbook involving the galaxies in this region.
Physical Information: Since NGC 6040 and its companion are interacting, they must be at the same distance, so the appropriate recessional velocity (relative to the Cosmic Microwave Background) to use to estimate their Hubble Flow distance is the average of their individual recessional velocities. For NGC 6040, that value is 12440 km/sec, while for its companion, it is 12350 km/sec, yielding an average of 12395 km/sec. Based on that (and H₀ = 70 km/sec/Mpc), a straightforward calculation indicates that Arp 122 is about 575 to 580 million light-years away (a single redshift-independent distance estimate of about 120 million light-years is obviously wrong, and probably belongs to a completely different object, showing that the confusion about the identification of the galaxies has caused at least some problems). 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 550 million light-years away at the time 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 about 1.4 by 0.45 arcmin (from the images below), the galaxy and its northwestern extensions span about 225 thousand light-years.

Historical Identification: As discussed in the entry for NGC 6040, some references treat PGC 56942 as part of the NGC object, and it is often misidentified as NGC 6039 (which see); but it is very unlikely that it had anything to do with Stephan's observation, and is treated as merely another 'apparent companion' in this catalog (albeit in this case, also as part of an Arp object).
Warning About Non-Standard Designation: Since there are no standards for the use of non-standard letter designations for NGC/IC objects, the use of such letters often leads to a given object being assigned more than one designation, and/or different objects being assigned the same designation. This can and has led to many instances of data belonging to one galaxy being assigned to a completely different one, so such non-standard designations should never be used except, as here, as a warning against their use. Of course in this particular case, the many misidentifications that don't involve letter designations have caused even more confusion, so it's almost like beating a dead horse to include this warning.
Use By The Arp Atlas: The Arp Atlas of Peculiar Galaxies lists Arp 122 as NGC 6039, presumably because of an incorrect identification of NGC 6039 as PGC 56942, and includes an image of what is supposedly that galaxy and NGC 6040 labeled as Arp 122, along with a note stating that they are part of the Hercules Cluster of galaxies. The pair is used by the Atlas as one of several examples of an elliptical galaxy (PGC 56942, misidentified as NGC 6039) close to and perturbing a spiral galaxy (NGC 6040).
Physical Information: As discussed in the entry for NGC 6040 (which see), it and its companion (PGC 56942), which comprise Arp 122, are about 550 million light-years away. Given that and its apparent size of about 1.05 by 0.95 arcmin (from the images below), PGC 56942 and its outer regions span about 165 to 170 thousand light-years.

Historical Identification: Per Dreyer, NGC 6042 (= GC 5801, Stephan list I (#2), 1860 RA 15 58 18, NPD 71 53.6) is "very faint, very small". The position precesses to RA 16 04 35.7, Dec +17 43 16, dead center on the galaxy listed above, the description fits and the other comparable galaxies in the region are accounted for by Stephan's list I #1 and #3, so the identification is certain.
Designation Note: As shown in the title for this entry, some references consider PGC 56960 to be part of NGC 6041, and the three designations shown after "with PGC 56960" all refer to the pair of galaxies. However, NGC 6041 is actually only PGC 56962, and PGC 56960 is not part of the NGC entry.
Note About PGC Designation: As shown in the title, HyperLEDA assigns PGC 3167946 as the designation for the pair of galaxies supposedly (but not) equal to NGC 6041; but a search of the database for that designation returns no result, so it is shown in quotes.
Physical Information: Based on a recessional velocity relative to the Cosmic Background Radiation of 10565 km/sec (and H₀ = 70 km/sec/Mpc), a straightforward calculation indicates that NGC 6041 is about 490 to 495 million light-years away, in reasonable agreement with redshift-independent distance estimates of about 390 to 490 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 470 to 475 million light-years away at the time the light by which we see it was emitted, about 480 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 ? arcmin (from the images below), the galaxy is about ? thousand light-years across.
NED Apparent size 1.3 by 1.1 arcmin.
Use By The de Vaucouleurs Atlas: NGC 6041 is used by the de Vaucouleurs Atlas of Galaxies as an example of galaxy type E⁺2 (gE). "gE" means "giant elliptical", while the "+" sign means that in the original Hubble-Shapley classification, this would be called an E/S0 galaxy. LEDA lists it as E/SB0, while NED lists it both as E and SB0, which is essentially the same but showing uncertainty in the classification. As a result, other than adding the "g" for "giant", I have used the LEDA designation for the type in the description line.

Physical Information: LEDA E1?, B 17.7, I 15.7, (V) 17(?); NED 3K Vr 101568 km/sec, z 0.033884545978

Physical Information: LEDA V 15.4; NED 15.4g, 3K Vr 11424 km/sec,
Apparent size 0.4 by 0.3? arcmin

Historical Identification: Per Dreyer, NGC 6042 (= GC 5801, Stephan list I (#3), 1860 RA 15 58 22, NPD 71 54.8) is "very faint, very small." The position precesses to RA 16 04 39.8, Dec +17 42 05, within the northeastern outline of the galaxy listed above, the description fits and there is nothing comparable nearby, so the identification is certain.
Note About The Duplicate Entry: Swift's earlier observation was 20 seconds of time to the west of the galaxy listed above (a not unusual error for Swift, as his method of determining right ascensions was awkward at best, and as a result, prone to errors), so Stephan and Dreyer thought that Stephan's discovery was of a completely different galaxy (there are a lot of them in the region, which is part of the Hercules Cluster of galaxies), hence the duplicate entry. But as discussed in the entry for NGC 6039, there is no other reasonable identification of Swift's object, so there is no question that this is an independent discovvery of the same object, and a duplicate listing.
Note About The Mistaken Identification As Arp 122: Early on, Swift's poor position led to some references identifying Swift's observation as the galaxy listed here, and others identifying it as the southern member of what became Arp 122 (or even as the northern member!). As a result of that, Arp and Vorontsov-Velyaminov both misidentified what became Arp 122 as NGC 6039, and since that is actually a duplicate observation observation of NGC 6042, the mistake should also be mentioned here, especially since some modern references (such as NED) insist on showing the wrong object, at the wrong position (though very strangely, the NED entry does have correct data for the galaxy listed here, even though it misidentifies the galaxy). As stated in the line immediately below, the reader should refer to NGC 6039 for anything else.
Physical Information: Given the duplicate listing, see NGC 6039 for anything else.

Historical Identification: Per Dreyer, NGC 6043 (Swift list IV (#22), 1860 RA 15 58 31, NPD 71 49.7) is "most extremely faint, pretty small, a little extended, '4th of 10'", being the next after NGC 6040, 6041 and 6039. The second IC lists a corrected RA (per Bigourdan) of 15 58 43.
Physical Information: A member of the Hercules Cluster of galaxies. Apparent size 0.8 by 0.4 arcmin.

Physical Information: Apparent size 0.2 by 0.05 arcmin. Recessional velocity (Vr 9290 km/sec, z 0.030981) similar to that of NGC 6043 (which see for images), so certainly in the same region (namely, the Hercules Cluster of galaxies), but not necessarily a close physical companion, the number of galaxies in the cluster being so large that some accidental "pairings" are inevitable.

Historical Identification: Per Dreyer, NGC 6044 (Swift list IV (#23), 1860 RA 15 58 33, NPD 71 43.7) is "most extremely faint, very small, round, very faint star close to west". Noted in Swift's paper as "5th of 10" after NGC 6040, 6041, 6039 and 6043.<
Physical Information: Apparent size 0.6 by 0.6? arcmin. Part of the Hercules Cluster of galaxies (for now, see NGC 6043 for an image)

Historical Identification: Per Dreyer, NGC 6045 (Swift list IV (#24), 1860 RA 15 58 38, NPD 71 50.7) is "most extremely faint, very small, round, very difficult". The second IC lists a corrected RA (per Bigourdan) of 15 58 49. Noted in Swift's paper as "6th of 10" after NGC 6040, 6041, 6039, 6043 and 6044.
Physical Information: Based on a recessional velocity of 9985 km/sec, a straightforward calculation indicates that NGC 6045 is about 465 million light-years away, in good agreement with redshift-independent distance estimates of 465 to 485 million light-years. Given that and its apparent size of 1.3 by 0.3 arcmin, it is about 175 thousand light-years across. As noted below, the apparent companion (PGC 84720) which led to its listing as Arp 71 is almost certainly a co-member of the Hercules Cluster, but may not actually be close enough to the larger galaxy to be physically interacting with it, and simply a slightly foreground object.

Physical Information: The 9350 km/sec recessional velocity of PGC 84720 is nearly 700 km/sec less than for NGC 6045, which corresponds to a separation of 30 million light-years. This means they are probably both members of the Hercules Cluster, but the smaller galaxy may be a foreground object, rather than a companion. In either case, PGC 84720's nearly 450 million light-year distance and apparent size of 0.4 by 0.05 arcmin corresponds to ? thousand light-years.

Physical Information: Apparent size 0.12 by 0.12 arcmin; apparently nothing else available. As a result, whether it has any relationship to NGC 6045 or is merely in nearly the same direction is unknown.

Historical Identification: Per Dreyer, NGC 6046 (= GC 4157 = WH III 33, 1860 RA 15 58 43, NPD 70 16.2) is "extremely faint, pretty large, partly verified".
Physical Information: Given the duplicate entry, see NGC 6028 for anything else.

Historical Identification: Per Dreyer, NGC 6047 (Swift list IV (#25), 1860 RA 15 58 43, NPD 71 53.2) is "extremely faint, round, pretty small, faint star close to north". Noted in Swift's paper as "7th of 10" after NGC 6040, 6041, 6039, 6043, 6044 and 6045.
Physical Information: Apparent size 1.1 by 0.8? arcmin. A member of the Hercules Cluster.

Historical Identification: Per Dreyer, NGC 6048 (= GC 4158 = WH II 873, 1860 RA 15 58 44, NPD 18 55.1) is "faint, round, brighter middle".
Physical Information: Apparent size 2.2 by 1.7? arcmin

Historical Identification: Per Dreyer, NGC 6049 (= GC 4159 = JH 1945, 1860 RA 15 58 51, NPD 81 31.3) is a "7th magnitude star in photosphere". Presumably glare from the star was mistakenly interpreted as a nebulous envelope.