Historical Identification: Per Dreyer, NGC 6550 (Stephan list XII (#87), 1860 RA 17 59 42, NPD 71 28.4) is "very faint, pretty small, round, several faint stars involved, near m 361", (Marth) 361 being NGC 6549. The second IC adds (erroneously) "6548 = 6550, Swift in Cat. XI.". Considerable confusion has reigned for more than a century as to the correct identification of NGC 6548, 6549, and 6550. NGC 6548 was discovered by William Herschel in 1786. That galaxy and NGC 6549 were observed by Albert Marth in 1864; and in 1880, Edouard Stephan observed three objects in the area -- undoubtedly Herschel and Marth's discoveries, and most likely an asterism which he mistook for a nebula. In compiling the NGC, Dreyer was uncertain which objects were which, and assigned separate numbers for each of the three "discoveries". However, (per Corwin) recent examination of the area makes it fairly certain that NGC 6550 is a mistaken repetition of NGC 6549 (which see for images). As an example of how confused the situation is, NED equates NGC 6548 and 6549, while HyperLeda equates NGC 6548 and 6550; so aside from the fact that both identifications now appear to be wrong, any data which supposedly apply to one NGC object may actually apply to another, and only the PGC listings (or some similar non-NGC identification) should be relied upon.
Physical Information: Given the duplicate entry, see NGC 6549 for anything else.

Historical Identification: Per Dreyer, NGC 6551 (Leavenworth list I (#230), 1860 RA 18 00 05, NPD 119 34.1) is "very faint, very small, round, partially resolved (some stars seen)". No object resembling Leavenworth's drawing exists anywhere near his recorded position. Since his drawing looks like a globular cluster, NGC 6551 is usually identified with the nearest globular cluster, NGC 6522 (for instance, the NGC/IC Project lists them as being the same). But aside from a huge error (more than a degree) in position, that object does not really look like his drawing, so even that identification is uncertain at best, and the most accurate description for NGC 6551 would be "lost".

Historical Identification: Per Dreyer, NGC 6552 (= GC 5893, d'Arrest, 1860 RA 18 00 14, NPD 23 23.7) is "faint, pretty small, irregularly round".
Physical Information: A Seyfert galaxy (type Sy2). Based on a recessional velocity of 7940 km/sec, NGC 6552 is about 370 million light years away. Given that and its apparent size of 1.0 by 0.7? arcmin, it is about 110 thousand light years across. NGC 6552 happens to lie fairly close to NGC 6543, the Cat's Eye Nebula, which is only about 10 arcmin to its west (as shown in the last image, below). However, since NGC 6552 is a distant galaxy, and NGC 6543 is only a few thousand light years away, their juxtaposition is merely coincidental.

Historical Identification: Per Dreyer, NGC 6553 (= GC 4378 = JH 3730 = WH IV 12, 1860 RA 18 00 44, NPD 115 56.3) is "a globular cluster, faint, large, a little extended, very gradually a little brighter middle, partially resolved (some stars seen), stars from 20th magnitude".
Physical Information: Apparent size 9.2? arcmin.

Historical Identification: Per Dreyer, NGC 6554 (= GC 4379 = JH 1995, 1860 RA 18 00 51, NPD 108 26.8) is "a cluster, pretty rich, very little compressed, stars large and small".
Physical Information: Apparent size 20? arcmin.

Historical Identification: Per Dreyer, NGC 6555 (= GC 4383 = WH II 902, Schultz, 1860 RA 18 00 57, NPD 72 24.9) is "faint, large, round, very gradually a little brighter middle". The second IC notes "RA is 18 01 38. Error in RA of Schultz's comparison star. Bigourdan's place agrees".
Physical Information: Apparent size 2.1 by 1.7? arcmin.

Historical Identification: Per Dreyer, NGC 6556 (= GC 4380 = JH 3732, 1860 RA 18 01 10, NPD 117 32.5) is "faint, very large, considerably extended, a little brighter middle, partially resolved (some stars seen)". The second IC notes (per Howe) "No nebulosity".
Physical Information: Apparent size ? arcmin.

Historical Identification: Per Dreyer, NGC 6557 (= GC 4381 = JH 3728, 1860 RA 18 01 11, NPD 116 36.7) is "very faint, very small, round, gradually a little brighter middle". The first IC adds the correction "NPD is 166 degrees, not 116".
Physical Information: Apparent size 1.6 by 1.1? arcmin.

Historical Identification: Per Dreyer, NGC 6558 (= GC 4382 = JH 3731, 1860 RA 18 01 12, NPD 121 46.8) is "a globular cluster, pretty bright, pretty large, round, gradually a little brighter middle, well resolved, clearly consisting of stars, stars from 16th magnitude." The position precesses to RA 18 10 18.1, Dec -31 45 38, nearly dead center on the cluster listed above, the description fits and there is nothing comparable nearby, so the identification is certain.
Discovery Notes: Gottlieb notes that Baracchi also observed the cluster with the 48-inch Great Melbourne Telescope and recorded "pretty bright, pretty small, round, gradually brighter middle, resolvable cluster of very minute stars." He also notes that it was described as "probably be classed as a globular" in the 1921 Helwan (observatory) list, based on photos taken in 1914-16.
Physical Information: The HST press release says that the cluster is about 23 thousand light-years away; this is in good agreement with Baumgardt's estimate of 23 to 25 thousand light-years. Estimates of the apparent size of the cluster range from about 3.7 arcmin on the low end, to 4.5 arcmin on the high end (hence my choice for the size of the circle in the close-up DSS image), but since such clusters always just fade into their surroundings in a rich field like this one, any apparent size is only an educated guess. The mass of the cluster is estimated at a little over 250 thousand Solar masses, and since most of its stars must have masses less than that of the Sun, there may be as many as half a million stars scattered over its (based on the distances and sizes noted above) roughly 30 light-year diameter. Calculations based on its current position and motion suggest that NGC 6558 makes about 50 orbits around the center of our galaxy every billion years, or something of the order of 600 such passes during its lifetime. Stripping of stars from its outer regions by the nucleus of our galaxy during each pass has undoubtedly removed many (if not most) of its original stars, resulting in its current moderate size.

Historical Identification: Per Dreyer, NGC 6559 (= GC 4384 = JH 1996 = JH 3733, 1860 RA 18 01 24, NPD 114 07.5) is "very faint, very large, a little extended, double star involved". The position precesses to RA 18 09 58.0, Dec -24 06 20, barely north of the midpoint of the double star at the center of the nebula listed above and the description fits, so the identification is certain. The only question is, out of the extended nebulosity in the region, what portion is NGC 6559? For the Herschels, "very large" meant a nebula about 8 to 10 arcmin in its largest dimension. This suggests that NGC 6559 is not only the reflection nebula centered on the double star, but also the emission region seen as a bright arc to the northwest of the stars; but to modern astrophotographers it sometimes "includes" the regions of absorption and reflection nebulae well to the east and west of Herschel's GC 4384, as shown in the wide-field images at the bottom of this entry.
About The PGC Designation: The Principal Galaxy Catalog is a catalog of relatively bright galaxies, and objects such as NGC 6559 were not included in the original catalog, or in its early revisions; but in the current HyperLEDA database, virtually all of the NGC/IC objects have been assigned PGC designations, such as the one shown in the title for this entry. However, a search of the database for the PGC designation returns no result, so it is shown in quotes.
Physical Information: NGC 6559 has an apparent size of about 10 by 7 arcmin (from the DSS wide-field image immediately below). This includes the reflection nebula centered on Herschel's double star, and the arc of bright emission to its northwest, as well as the fainter regions directly associated with those features, and agrees with Herschel's estimate of the size of the nebula. (The fainter regions shown in the wider-field images are not part of NGC 6559, but are sometimes referred to as if they were.) The nebula and star cluster forming inside the reflection nebula are about 5000 light years away, so based on its apparent size, NGC 6559 is about 15 light years across.

Historical Identification: Per Dreyer, NGC 6560 (Swift list V (#84), 1860 RA 18 01 28, NPD 43 07.1) is "most extremely faint, pretty small, irregularly round".
Physical Information: Apparent size 1.2 by 0.8? arcmin.

Historical Identification: Per Dreyer, NGC 6561 (= GC 4385 = JH 1997 = WH VIII 54, 1860 RA 18 02 25, NPD 106 49.0) is "a cluster, large, a little compressed, stars considerably large" (meaning relatively bright). The position precesses to RA 18 10 31.8, Dec -16 47 41, but there is no obvious cluster in the region. Until recently, though some catalogs listed one position or another for this object, most listed it as nonexistent. However, a 2002 catalog of clusters based on proper motions of stars in various historical catalogs suggests that a group of moderately bright stars centered on the position listed above is probably the otherwise lost NGC 6561. Deciding whether that suggestion is reasonable depends upon interpreting the Herschels' description of the cluster according to their observing conditions. A modern photograph of the region shows a densely crowded stellar field, and seeing any "cluster" is difficult. But adjusting the brightness limits of the image to more closely match those faced by visual observers of two centuries ago, a wide scattering of "considerably large" stars can be seen, centered on a point about 3 arcmin to the north of the NGC position. As a result, it seems more likely than not that the star group more or less centered on the position listed above is what the Herschels observed, and should be listed as NGC 6561.
Physical Information: About 15 by 20 arcmin apparent size. Distance about 11000 ly, making the group about 50 light years across. Based on color excess of supposed members of the group, its age is about 8 million years.

Above and below, 30 arcmin wide DSS images of the region near NGC 6561. The image above is centered on the NGC position for the cluster, and is shown as usually imaged in such photographic databases. The image below is centered at the position listed in this entry, and is adjusted to better approximate the visual appearance of the region. Comparing the images shows that there is a somewhat extensive but sparsely populated group of relatively bright stars centered just to the north of the NGC position, hence my decision to accept the recent identification as probably correct.

Historical Identification: Per Dreyer, NGC 6562 (Swift list I (#85), 1860 RA 18 02 42, NPD 33 45.2) is "faint, pretty small, round, brighter middle, between 2 stars".
Physical Information: Apparent size 0.7 by 0.7? arcmin.

Historical Identification: Per Dreyer, NGC 6563 (= GC 4386 = JH 3734, (Dunlop 606), 1860 RA 18 02 48, NPD 123 53.5) is "a planetary nebula, faint, large, considerably extended, hazy border".
Discovery Notes: Neither Dreyer nor Herschel was aware of the possibility that Dunlop observed this object, but it is now thought that it is Dunlop 606, hence the reference in parentheses.
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: Apparent size 0.8? arcmin.

Historical Identification: Per Dreyer, NGC 6564 (= GC 5894, Marth #362, 1860 RA 18 02 52, NPD 72 37) is "extremely faint, very small".

Historical Identification: Per Dreyer, NGC 6565 (Pickering (HN 42), 1860 RA 18 03 03, NPD 118 12) is "a planetary nebula, stellar".
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: Apparent size 0.23? arcmin.

Historical Identification: Per Dreyer, NGC 6566 (= GC 4387, d'Arrest, 1860 RA 18 03 51, NPD 37 44.0) is "extremely faint, very small, round, 16th magnitude star near".
Physical Information: Apparent size 0.6 by 0.6? arcmin.

Historical Identification: Per Dreyer, NGC 6567 (Pickerig (HN 49), 1860 RA 18 04 02, NPD 109 07) is "a planetary nebula, stellar, 11th magnitude, in a cluster".
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: Apparent size 0.20? arcmin.

Historical Identification: Per Dreyer, NGC 6568 (= GC 4388 = JH 1998 = JH 3735 = WH VII 30, 1860 RA 18 04 21, NPD 111 37.6) is "a cluster, very large, a little compressed".
Physical Information: Apparent size 12? arcmin.

Historical Identification: Per Dreyer, NGC 6569 (= GC 4389 = JH 3736 = WH II 201, Dunlop 619, 1860 RA 18 04 33, NPD 121 51.0) is "a globular cluster, considerably bright, large, round, well resolved, clearly consisting of stars, stars from 15th magnitude." The position precesses to RA 18 13 39.4, Dec -31 49 09, well within the cluster listed above, the description fits and there is nothing else nearby, so the identification is certain.
Physical Information: NGC 6569 is a globular cluster orbiting more or less within the galactic disk (never being more than about 3000 light-years from the central disk), but outside the galaxy's central bulge (its perigalaxion is about 8 to 9 thousand light-years, while its apogalaxion is about 33 to 37 thousand light-years). Its orbital period is about 40 to 45 million years, and each orbital pass is somewhat rotated relative to its original position. Since the cluster is about 12 billion years old, that means that it has orbited the galactic center about 280 (give or take about 20) times since it was formed. It is thought to have about 240 thousand times the mass of the Sun, but since its current stellar population consists mostly of stars fainter and less massive than the Sun, it probably has between 350 and 400 thousand stars and binary systems inside it. At the present time it is near apogalaxion, but headed inward, so it will reach perigalaxion in about 20 million years. The apparent size of the cluster is about 6.5 arcmin (give or take about an arcmin, since it is hard to tell exactly where such clusters fade into the general stellar background). It is currently about 33 to 36 thousand light-years from the Sun, which implies that it is about 60 to 70 light-years in diameter, though half its mass is thought to lie within a region only about 30 light-years across.

Historical Identification: Per Dreyer, NGC 6570 (= GC 5895, Marth #363, d'Arrest, 1860 RA 18 04 46, NPD 75 56.4) is "pretty faint, pretty large, round".
Physical Information: Apparent size 1.9 by 1.1? arcmin.

Historical Identification: Per Dreyer, NGC 6571 (= GC 5896, Marth #364, 1860 RA 18 04 51, NPD 68 48) is "extremely faint, very small, stellar".
Physical Information: Apparent size 0.4 by 0.4? arcmin.

Historical Identification: Per Dreyer, NGC 6572 (= GC 4390 = JH 2000, Struve 6, 1860 RA 18 05 18, NPD 83 10.5) is "a planetary nebula, very bright, very small, round, a little hazy".
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: Apparent size 0.25? arcmin.

Historical Identification: Per Dreyer, NGC 6573 (= GC 4391 = JH 1999, 1860 RA 18 05 24, NPD 112 10.8) is "a cluster, stars very small" (meaning very faint).
Physical Information: Apparent size 6? arcmin.

Historical Identification: Per Dreyer, NGC 6574 (= GC 5897, Marth #365, 1860 RA 18 05 30, NPD 75 03) is "pretty bright, small, round".
Physical Information: Apparent size 1.5 by 1.1? arcmin.

Historical Identification: Per Dreyer, NGC 6575 (Stephan list XII (#??), (Safford 33), 1860 RA 18 05 40, NPD 58 54.7) is "pretty bright, small, round"
Discovery Notes: Safford's observations were not published until long after he made them, so Stephan's discovery was independent; and Dreyer did not become aware of them until the NGC was nearly ready for publication, so they are only noted in an appendix and none appear in the individual NGC entries (hence the use of parentheses to show that Safford's observation was not actually in Dreyer's entry).
Physical Information: Apparent size 1.8 by 1.3? arcmin.

Historical Identification: Per Dreyer, NGC 6576 (= GC 5898, Marth #366, 1860 RA 18 05 51, NPD 68 35) is "extremely faint, very small".
Physical Information: Apparent size 0.6 by 0.6? arcmin.

Historical Identification: Per Dreyer, NGC 6577 (= GC 5899, Marth #367, 1860 RA 18 06 04, NPD 68 34) is "very faint, small".
Physical Information: Apparent size 1.5 by 1.3? arcmin.

Historical Identification: Per Dreyer, NGC 6578 (Pickering (HN 47), 1860 RA 18 06 33, NPD 110 19) is "a planetary nebula, stellar, equal to 13th magnitude star".
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: A distance estimate (per Palen and Balick) based on HST images at different epochs is 6000 light years, with an uncertainty of about 2000 light years. Given that and an apparent size of 0.18 arcmin, the nebula is about a third of a light year across. The distance estimate is based on a comparison of the expansion rate of the nebula (about 12 miles per second) to its apparent change in size during the interval between the epochs. The accuracy of this technique increases with time, so future efforts should gradually improve our knowledge of the nebula's distance.

Historical Identification: Per Dreyer, NGC 6579 (= GC 5900, Marth #368, 1860 RA 18 06 35, NPD 68 36) is "faint, western of double nebula", the other being NGC 6580. The second IC lists a corrected RA (per Bigourdan) of 18 06 23.
Physical Information: Apparent size 0.4 by 0.4? arcmin. 4965 km/sec recessional velocity. An apparent companion of NGC 6580, but the difference in recessional velocity corresponds to a 40 million light year difference in distance, so they are probably an optical double.

Historical Identification: Per Dreyer, NGC 6580 (= GC 5901, Marth #369, 1860 RA 18 06 37, NPD 68 36) is "faint, eastern of double nebula", the other being NGC 6579. The second IC lists a corrected RA (per Bigourdan) of 18 06 25.
Physical Information: Apparent size 1.3 by 0.7? arcmin. 5843 km/sec recessional velocity. An apparent companion of NGC 6579 (which see for images), but the difference in recessional velocity corresponds to a 40 million light year difference in distance, so they are probably an optical double.

Historical Identification: Per Dreyer, NGC 6581 (= GC 5902, Stephan list I (#9), 1860 RA 18 06 51, NPD 64 22.8) is "extremely faint, diffuse, between 2 faint stars".
Physical Information: Apparent size 0.4 by 0.4? arcmin.

Historical Identification: Per Dreyer, NGC 6582 (Swift list IV (#67), 1860 RA 18 07 23, NPD 40 06.8) is "most extremely faint, pretty small, round".
Physical Information: Apparent size of PGC 61510 = 0.6 by 0.6? arcmin. Apparent size of PGC 61513 = 0.8 by 0.8? arcmin.

Historical Identification: Per Dreyer, NGC 6583 (= GC 4392 = JH 2001 = JH 3739 = WH VII 31, 1860 RA 18 07 24, NPD 112 10.4) is "a cluster, pretty rich, pretty compressed, considerably extended, stars from 13th magnitude".
Physical Information: Apparent size 5? arcmin.

Historical Identification: Per Dreyer, NGC 6584 (= GC 4393 = JH 3737, Dunlop 376, 1860 RA 18 07 25, NPD 142 15.2) is "a globular cluster, considerably bright, considerably large, round, gradually much brighter middle, well resolved, clearly consisting of stars, stars from 15th magnitude".
Physical Information: Apparent size 6.6? arcmin.

Historical Identification: Per Dreyer, NGC 6585 (Swift list VI (IX #87), 1860 RA 18 07 34, NPD 50 21.2) is "most extremely faint, small, extremely extended, between several bright stars".
Discovery Notes: This is one of several objects included in a pre-publication version of Swift's list VI sent to Dreyer in 1887 that were inadvertently omitted from the published paper; for most of the objects, including this one, the omission was corrected by including them in Swift's list IX, whence the reference in parentheses.
Physical Information: Apparent size 1.9 by 0.4? arcmin.

Historical Identification: Per Dreyer, NGC 6586 (= GC 5903, Marth #370, 1860 RA 18 07 38, NPD 68 57) is "extremely faint, small, round".
Physical Information: Apparent size 0.9 by 0.5? arcmin.

Historical Identification: Per Dreyer, NGC 6587 (= GC 5904, Marth #371, 1860 RA 18 07 43, NPD 71 13) is "faint, very small, round, stellar".
Physical Information: Apparent size 1.3 by 1.1? arcmin.

Historical Identification: Per Dreyer, NGC 6588 (= GC 4394 = JH 3738, 1860 RA 18 07 57, NPD 153 51.3) is "extremely faint, small, 6th magnitude star to southwest". The second IC notes (per DeLisle Stewart) "Not seen, several very faint stars, no nebulosity".
Physical Information:

Historical Identification: Per Dreyer, NGC 6589 (Swift list II (#??), (Safford 81), 1860 RA 18 07 59, NPD 109 50.3) is "a double star in center of extremely faint, pretty large nebulosity". The first IC adds "Place is RA 18 08 35, NPD 109 48.9, and 6590 = 6595 (Barnard, A.N. 3101)".
Discovery Notes: Safford's observations were not published until long after they were made, so Swift's discovery was independent; and since Dreyer's NGC was nearly ready for publication when he became aware of them, he only noted them in an appendix and none were included in individual NGC entries (hence the use of parentheses in the entry shown here).
Physical Information: Apparent size 5.0 by 3.0? arcmin.

Historical Identification: Per Dreyer, NGC 6590 (Swift list II (#62), 1860 RA 18 08 01, NPD 109 55.3) is "a double star in center of pretty faint, pretty large, round nebulosity". The first IC adds (in a comment about 6589) "Place is RA 18 08 35, NPD 109 48.9, and 6590 = 6595 (Barnard, A.N. 3101)".
Physical Information: Apparent size 11? arcmin.

Historical Identification: Per Dreyer, NGC 6591 (= GC 5905, Marth #372, 1860 RA 18 08 02, NPD 68 59) is "most extremely faint, very small, stellar".
Physical Information: Apparent size 0.3 by 0.1? arcmin.

Historical Identification: Per Dreyer, NGC 6592 (Swift list I (#86), 1860 RA 18 08 10, NPD 28 36.3) is "very faint, very small, round".
Physical Information: Apparent size 0.5 by 0.4? arcmin.

Historical Identification: Per Dreyer, NGC 6593 (= GC 5906, Marth #373, Stephan list VII (#??), 1860 RA 18 08 10, NPD 67 45.2) is "very faint, very small, round, a little brighter middle".
Physical Information: Apparent size 0.8 by 0.4? arcmin.

Historical Identification: Per Dreyer, NGC 6594 (Swift list I (#87), 1860 RA 18 08 34, NPD 28 53.6) is "very faint, very small, round".
Physical Information: Apparent size 1.0 by 0.7? arcmin.

Historical Identification: Per Dreyer, NGC 6595 (= GC 4395 = JH 2002, 1860 RA 18 08 47, NPD 109 55.1) is "faint, pretty large, considerably extended, double star involved". The first IC adds (in a comment about 6589) "Place is RA 18 08 35, NPD 109 48.9, and 6590 = 6595 (Barnard, A.N. 3101)".
Physical Information: Given the duplicate entry, see NGC 6590 for anything else.

Historical Identification: Per Dreyer, NGC 6596 (= GC 4396 = JH 2003 = WH VIII 55, 1860 RA 18 09 28, NPD 106 41.4) is "a cluster, a little compressed".
Physical Information: Apparent size 10? arcmin.

Historical Identification: Per Dreyer, NGC 6597 (Swift list I (#89), 1860 RA 18 09 34, NPD 28 51.1) is "very faint, very small, round, bright star near".
Physical Information: Apparent size 0.8 by 0.4? arcmin.

Historical Identification: Per Dreyer, NGC 6598 (Swift list I (#88), 1860 RA 18 09 50, NPD 20 58.6) is "extremely faint, pretty small, round". The position precesses to RA 18 08 52.2, Dec +69 03 19, just over an arcmin to the southwest of the galaxy; given the galaxy's size and proximity and the lack of any other nearby objects, the identification is certain.
Physical Information: Based on a recessional velocity of 8310 km/sec, NGC 6598 is about 390 million light years away. Given that and its apparent size of 2.0 by 1.4 arcmin, it is about 225 thousand light years across.

Historical Identification: Per Dreyer, NGC 6599 (Stephan list XII (#89), 1860 RA 18 09 59, NPD 65 07.8) is "pretty faint, very small, round, gradually brighter middle, small star attached on east".
Physical Information: Apparent size 1.3 by 1.2? arcmin