Celestial Atlas
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Page last updated Mar 22, 2017
WORKING 6610: Adding Dreyer NGC entries
WORKING 6600: Add/update Steinicke listings/data, check IDs

NGC 6600 (=
NGC 6599 = PGC 61655)
Discovered (Jun 6, 1864) by Albert Marth (and later listed as NGC 6600)
Discovered (Jul 27, 1880) by Édouard Stephan (and later listed as NGC 6599)
A 13th-magnitude lenticular galaxy (type S0?) in Hercules (RA 18 15 42.9, Dec +24 54 47)
Historical Identification: Per Dreyer, NGC 6000 (= GC 5907, Marth #374, 1860 RA 18 09 59, NPD 65 01) is "faint, very small, stellar".
Physical Information: Given the duplicate listing, see NGC 6599 for anything else.

NGC 6601 (= PGC 61533)
Discovered (Aug 4, 1883) by
Lewis Swift
Also observed (date?) by Guillaume Bigourdan
A 15th-magnitude lenticular galaxy (type E/S0?) in Draco (RA 18 11 44.2, Dec +61 27 11)
Historical Identification: Per Dreyer, NGC 6601 (Swift list i (#90), 1860 RA 18 10 05, NPD 28 35.1) is "extremely faint, pretty small, round". The second IC lists a corrected RA (per Bigourdan) of 18 10 48.
Physical Information: Apparent size 0.5 by 0.3? arcmin.

NGC 6602 (= PGC 61674)
Discovered (Jul 1, 1886) by
Guillaume Bigourdan
A 14th-magnitude spiral galaxy (type SB??) in Hercules (RA 18 16 34.2, Dec +25 02 37)
Historical Identification: Per Dreyer, NGC 6602 (Bigourdan (list II #83), 1860 RA 18 10 10, NPD 65 00) is "a cluster, very small, stars faint, 30 arcsec (wide), nebulous?"
Physical Information: Apparent size 1.0 by 0.7? arcmin.

NGC 6603 (= OCL 36)
In region observed (Jun 20, 1764) by
Charles Messier (and recorded as M24)
Discovered (Jul 15, 1830) by John Herschel
An 11th-magnitude open cluster (type I1r) in Sagittarius (RA 18 18 24.0, Dec -18 24 24)
Historical Identification: Per Dreyer, NGC 6603 (= GC 4397 = JH 2004, M 24, 1860 RA 18 10 14, NPD 108 28.1) is "a remarkable object, a cluster, very rich, very much compressed, round, stars from 15th magnitude (in the Milky Way)".
Discovery Notes: Though Dreyer lists this as M24, that is a (much larger) star cloud and not the cluster recorded by Herschel.
Physical Information: Apparent size 4.0? arcmin.

NGC 6604 (= OCL 56)
Discovered (Jul 15, 1784) by
William Herschel
Also observed (date?) by John Herschel
A 7th-magnitude open cluster (type I3p) in Serpens (RA 18 18 06.0, Dec -12 13 00)
Historical Identification: Per Dreyer, NGC 6604 (= GC 4398 = JH 3740 = WH VIII 15, 1860 RA 18 10 14, NPD 102 17.2) is "a cluster, a little rich, a little compressed".
Physical Information: Apparent size 6? arcmin.

NGC 6605 (= OCL 47)
Discovered (Jul 31, 1826) by
John Herschel
A 6th-magnitude open cluster in Serpens (RA 18 16 24.0, Dec -15 00 00)
Historical Identification: Per Dreyer, NGC 6605 (= GC 4399 = JH 2005, 1860 RA 18 10 21, NPD 104 59.6) is "a cluster, a little rich, a little compressed, stars from 10th to 12th magnitude".
Physical Information: Apparent size 29? arcmin.

NGC 6606 (= PGC 61633)
Discovered (Aug 8, 1883) by
Édouard Stephan
A 14th-magnitude spiral galaxy (type Sb?) in Lyra (RA 18 14 41.3, Dec +43 16 07)
Historical Identification: Per Dreyer, NGC 6606 (Stephan list XIII (#88), 1860 RA 18 10 27, NPD 46 46.7) is "very faint, small, round, gradually brighter middle, very faint star involved".
Physical Information: Apparent size 0.9 by 0.7? arcmin.

NGC 6607 (= PGC 61550)
Discovered (Aug 4, 1883) by
Lewis Swift
Looked for but not found (date?) by Herbert Howe
A magnitude 15.3 spiral galaxy (type Sbc?) in Draco (RA 18 12 14.9, Dec +61 20 00)
Historical Identification: Per Dreyer, NGC 6607 (Swift list I (#91), 1860 RA 18 10 29, NPD 28 42.3) is "extremely faint, pretty small, round, very difficult". The second IC states "Not found by Howe (3 nights)", suggesting a poor position, but the position precesses to RA 18 11 57.8, Dec +61 19 59, only about 2 arcmin due west of the galaxy listed above, and a considerably brighter galaxy (which must be NGC 6608 or 6609, listed by Swift as being 15 and 20 seconds of time to the east) is clearly visible about 19 seconds of time to the east. So the problem is not the position, which is not a bad one for Swift, but the fact that the galaxy is relatively diffuse and hard to see. In any event, the close correspondence of relative positions and descriptions for this and NGC 6608/9 (which have essentially identical desciptions) make the identification of NGC 6607 certain.
Physical Information: Based on a recessional velocity of 6775 km/sec (and H0 = 70 km/sec/Mpc), NGC 6607 is about 315 million light years away. Given that and its apparent size of about 0.6 by 0.55 arcmin (from the images below) it is about 55 thousand light years across.
DSS image of region near spiral galaxy NGC 6607, also showing NGC 6008
Above, a 12 arcmin wide DSS image centered on NGC 6007, also showing NGC 6608
Below, a 1 arcmin wide DSS image of the galaxy
DSS image of spiral galaxy NGC 6607
Below, a 1 arcmin wide PanSTARRS image of the galaxy
PanSTARRS image of spiral galaxy NGC 6607

NGC 6608 (almost certainly =
NGC 6609 = PGC 61559)
Discovered (Aug 4, 1883) by Lewis Swift
Looked for but not found (date?) by Herbert Howe
A magnitude 14.5 lenticular galaxy (type S0?) in Draco (RA 18 12 33.6, Dec +61 19 56)
Historical Identification: Per Dreyer, NGC 6608 (Swift list I (#92), 1860 RA 18 10 44, NPD 28 42.1) is "very faint, extremely small, round, very faint star near". The second IC states "Not found by Howe (2 nights); = 6609?". The position precesses to RA 18 12 12.8, Dec +61 20 14, almost dead center on PGC 61550 (= NGC 6607), which does not fit the description, and about 2.5 arcmin nearly due west of the galaxy listed above, which perfectly matches the description. Under normal circumstances the nearly identical positional error (and the correspondingly good relative position) of the two galaxies would be considered certain proof of their identity; but there is a problem, in that Swift lists two galaxies to the east of NGC 6607, separated by only 5 seconds of time, and there is only one galaxy there. As suggested by the second IC note, the solution is probably that the "two galaxies" are actually a duplicate listing of the same galaxy, but they were supposedly observed on the same night, presumably at nearly the same time, making it hard to understand how Swift could have made such a mistake. For reasons discussed in the Discovery Notes for this entry, a duplicate entry is the most likely scenario, but as noted by Corwin, this is one of the most puzzling problems posed by Swift's observations. Still, in the light of the discussion below, the second IC solution (NGC 6608 being a duplicate observation of NGC 6609) is almost certainly correct, as noted in the title of this entry.
Discovery Notes: There is, unfortunately, another possible albeit very unlikely solution to this problem. Namely, 5 seconds west of PGC 61559 and 2 arcmin to the south, there is a third galaxy in the region; and if we ignore problems with the description of NGC 6608 and the appearance of that galaxy, it would seem obvious that NGC 6608 is actually that galaxy, with an error in its NPD. The problem is that PGC 61556, the galaxy to the south, is not considerably brighter than NGC 6607, as the description for NGC 6608 suggests, but even fainter. In fact Steve Gottlieb, in discussing his observations of the region, notes that even NGC 6607 would have been a difficult object for Swift to observe, and the fainter PGC 61556 almost certainly impossible for him to see. In addition, its appearance does not match the description for NGC 6608, and there is no "very faint star near" it, as there is near PGC 61559. Despite these problems, the urge to attach the three NGC entries to three galaxies and the presence of this third galaxy means that for most of the last few decades PGC 61556 has been (almost certainly mis-)identified as NGC 6608 (save for a few unfortunate occasions on which it has been misidentified as NGC 6609, which is absolutely and certainly incorrect). Given that history, PGC 61556 is discussed in the following entry, though more as a warning about its certain misidentification as NGC 6609 and its probable misidentification as NGC 6608 than as a serious candidate for the latter entry.
Physical Information: Based on a recessional velocity of 8150 km/sec, a straightforward calculation (with H0 = 70 km/sec/Mpc) indicates that NGC 6608 is about 380 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 365 to 370 million light years away at the time the light by which we see it was emitted, about 370 to 375 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 0.9 by 0.65 arcmin (from the images below), the galaxy is about 95 thousand light years across.
DSS image of region near lenticular galaxy NGC 6608, also showing NGC 6607 and PGC 61556 (which is often misidentified as NGC 6608 or NGC 6609)
Above, a 12 arcmin wide DSS image centered on NGC 6608, also showing NGC 6607 and PGC 61556
Below, a 1 arcmin wide DSS image of the galaxy
DSS image of lenticular galaxy NGC 6608
Below, a 1 arcmin wide PanSTARRS image of the galaxy
PanSTARRS image of lenticular galaxy NGC 6608

PGC 61556 (probably not =
NGC 6608 and certainly not NGC 6609)
A magnitude 15.1 spiral galaxy (type Scd?) in Draco (RA 18 12 29.2, Dec +61 17 55)
Historical Misidentification: See the Discovery Notes for NGC 6608 for a discussion of why PGC 61556 is probably not that object, and for NGC 6609 for a discussion of why it is certainly not that object.
Physical Information: Based on a recessional velocity of 6720 km/sec (and H0 = 70 km/sec/Mpc), PGC 61556 is about 310 to 315 million light years away, in poor agreement with redshift-independent distance estimates of about 465 to 470 million light years. Using the smaller distance, its apparent size of about 0.8 by 0.1 arcmin (from the images below) is about 70 to 75 thousand light years. The larger distance would yield a physical size of about 105 to 110 thousand light years.
DSS image of lenticular galaxy PGC 61556, which is often misidentified as NGC 6608 or NGC 6609
Above, a 1 arcmin wide DSS image of PGC 61556 (see NGC 6608 for a wider view)
Below, a 1 arcmin wide PanSTARRS image of the galaxy
PanSTARRS image of lenticular galaxy PGC 61556, which is often misidentified as NGC 6608 or NGC 6609

NGC 6609 (almost certainly =
NGC 6608 = PGC 61559)
Discovered (Aug 4, 1883) by Lewis Swift
A magnitude 14.5 lenticular galaxy (type S0?) in Draco (RA 18 12 33.6, Dec +61 19 56)
Historical Identification: Per Dreyer, NGC 6609 (Swift list I (#93), 1860 RA 18 10 49, NPD 28 42.1) is "very faint, pretty small, a little extended, faint star near". In a note about NGC 6608, the second IC states "Not found by Howe (2 nights); = 6609?". (Given the nearly identical positions and descriptions of NGC 6608 and 6609 and the fact that there is only one galaxy in the region that could fit the descriptions, the suggestion of a duplicate entry is almost certainly correct; but as discussed in the Discovery Notes for NGC 6608, that is one of the more puzzling of Swift's observations, and as a result the duplicate entry is only "almost certainly correct", and not "certain".) As noted in the entry for NGC 6608 it is hard to see how Swift could have mistakenly listed two observations for the same galaxy when the observations were made on the same night, presumably at nearly the same time. But the fact that the descriptions are essentially identical and only match one galaxy in the region makes a duplicate entry the only truly reasonable (even if puzzling) solution to the problem. In any event, the position precesses to RA 18 12 17.8, Dec +61 20 15, just east of NGC 6607 and about 1.9 arcmin nearly due west of the galaxy listed above. The descriptions and relative positions of NGC 6607 and 6609 make their identification essentially certain, the only question being whether NGC 6608 is truly a duplicate observation of NGC 6609.
Discovery Notes: As noted in the previous two entries, PGC 61556 is usually (almost certainly mis-)identified as NGC 6608, and even (all too often) misidentified as NGC 6609. There is some rationale for wishing PGC 61556 to be NGC 6608, there being three NGC entries in the region and three galaxies, and even though PGC 61556 is almost certainly too faint for Swift to have seen, and does not in any way match his description of NGC 6608, it makes a tempting even if very unlikely candidate. However, there is absolutely no excuse for misidentifying it as NGC 6609, and that can only be considered a blunder (meaning an error so blatant that it makes one cringe).
Physical Information: Given the almost certain duplicate entry, see NGC 6608 for anything else.

WORKING HERE: Adding Dreyer NGC entries

NGC 6610 (=
NGC 6574 = PGC 61536)
Discovered (Jul 9, 1863) by Albert Marth (and later listed as NGC 6574)
Discovered (Jul 13, 1876) by Édouard Stephan (7-21) (and later listed as NGC 6610)
A 12th-magnitude spiral galaxy (type SBbc?) in Hercules (RA 18 11 51.2, Dec +14 58 54)
Historical Identification:
Physical Information: Given the duplicate entry, see NGC 6574 for anything else.

NGC 6611 (=
M16 = OCL 54), an open cluster in The Eagle Nebula
(associated with IC 4703)

Discovered (1745) by Philippe de Chéseaux
Observed (Jun 3, 1764) by Charles Messier and listed as M16
Rediscovered (1783) by William Herschel
Listed by Dreyer as discovered (1836) by John Herschel
A 6th-magnitude open cluster (type II3mn) in Serpens (RA 18 18 45.0, Dec -13 47 54)
Historical Identification: Dreyer's precessed position is a few seconds east and 1.5 arcmin north of the "standard" position, but in comparison to the size of the cluster the discrepancy is minor; so there is no doubt of the identification. Although de Chéseaux discovered the cluster in the 1740's, his only publication of his discoveries was a report to the French Academy of Sciences which was more or less forgotten until Guillaume Bigourdan published a note about de Cheseaux in 1892; so when Dreyer published the New General Catalog, which was primarily an updating and expansion of John Herschel's General Catalog, he credited John Herschel as the discoverer. Why he didn't credit Messier, or John's father William Herschel, is not obvious at this writing. (Far more to follow...)
Physical Information: The Eagle Nebula and the young star cluster associated with it are about 7000 light years away, meaning we see them as they were 7000 years ago. But up to the left of the brightest part of the nebula, where the star cluster is centered, is a violently expanding cloud of gas caused by a supernova which took place a few thousand years beforehand. Estimates are that six thousand years ago, high-velocity supernova gases slammed into, compressed and simultaneously tore apart the so-called "Pillars of Creation" near the center of the nebula (though we won't see that until a millennium from now). In the process, most of the clouds of gas and dust visible here would be torn apart, but some of the denser nodules hidden inside the Pillars would be violently compressed to quickly form bright new stars. In fact, in such regions close to half the bright stars formed are the result of such events, and for lower mass stars like our Sun, compression by expanding gases is almost always the cause of their formation.
NOAO image of NGC 6611, an open cluster in the Eagle Nebula, also known as M16
Above, a ? arcmin wide view of the region near NGC 6611 (click here for a much larger version)
(T.A.Rector (NRAO/AUI/NSF and NOAO/AURA/NSF) and B.A.Wolpa (AURA/NSF), NOAO)
Below, a ? arcmin wide (cropped) view of the image above
Closeup of NOAO image of open cluster NGC 6611, part of the Eagle Nebula, or M16
Below, a ? arcmin wide HST image of the "Pillars of Creation", a star-forming region now long-gone
(Image Credits: J. Hester, P. Scowen (ASU), NASA, HST)
HST image of the Pillars of Creation in the Eagle Nebula
Below, a 2014 update of the image above shows how hot gases are eating away the 'pillars'
(Image Credit NASA/ESA/Hubble Heritage Team (STScI/AURA)/J. Hester, P. Scowen (Arizona State U.))
HST image of the Pillars of Creation and the region surrounding them, showing how they are being eaten away by hot gases streaming past and compressing them

NGC 6612 (= PGC 61665)
Discovered (1886) by
Lewis Swift (6-?)
A 14th-magnitude lenticular galaxy (type E/S0?) in Lyra (RA 18 16 10.8, Dec +36 04 43)
Historical Identification:
Physical Information: Apparent size 0.45 by 0.45 arcmin.
DSS image of region near lenticular galaxy NGC 6612
Above, a 12 arcmin wide DSS image centered on NGC 6612
Below, a 0.6 arcmin wide DSS image of the galaxy
DSS image of lenticular galaxy NGC 6612

NGC 6613 (=
M18 = OCL 40)
Discovered (Jun 3, 1764) by Charles Messier (and recorded as M18)
A 7th-magnitude open cluster (type II3pn) in Sagittarius (RA 18 19 58.0, Dec -17 06 06)
Historical Identification:
Physical Information: NGC 6613 is a loose collection of about 20 stars, spread over a region about 15 to 20 light-years in diameter, four to six thousand light-years from the Sun (its size being based on its estimated distance, and its apparent size of 7.0 arcmin). Its hottest, brightest members are of the relatively 'early' spectral type B3, which means it is probably about 30 million years old.
NOAO view of open cluster NGC 6613, also known as M18
Above, a ? arcmin wide image of NGC 6613 (Image Credit: Hillary Mathis, REU program, AURA, NSF, NOAO)

NGC 6614 (= PGC 61852)
Discovered (Jun 20, 1835) by
John Herschel
A 13th-magnitude lenticular galaxy (type E/SB0?) in Pavo (RA 18 25 07.3, Dec -63 14 54)
Historical Identification:
Physical Information: Apparent size 1.4 by 1.1? arcmin

NGC 6615 (= PGC 61713)
Discovered (Jul 9, 1863) by
Albert Marth (375)
A 13th-magnitude lenticular galaxy (type SB0/a?) in Ophiuchus (RA 18 18 33.4, Dec +13 15 55)
Historical Identification:
Physical Information: Apparent size 1.3 by 0.9? arcmin

NGC 6616 (= PGC 61693)
Discovered (Jul 14, 1885) by
Lewis Swift (2-64)
Also observed by Herbert Howe
A 14th-magnitude spiral galaxy (type Sab?) in Hercules (RA 18 17 41.0, Dec +22 14 16)
Historical Identification: The second IC adds (per Howe) "RA is 18 11 47, the 2 stars are 9th to 10th magnitude, one 2 seconds west and 0.6 arcmin south".
Physical Information: Apparent size 1.4 by 0.6? arcmin.

NGC 6617 (= PGC 61613)
Discovered (Jun 14, 1885) by
Lewis Swift (1-94)
A 15th-magnitude spiral galaxy (type Scd?) in Draco (RA 18 14 02.9, Dec +61 19 10)
Historical Identification:
Physical Information: Apparent size 1.1 by 0.7? arcmin

NGC 6618 (=
M17 = OCL 44, the Swan, or Omega Nebula)
Discovered (1745) by Phillipe de Cheseaux
Recorded (Jun 3, 1764) by Charles Messier and listed as M17
A 5th-magnitude emission nebula and open cluster in Sagittarius (RA 18 20 47.0, Dec -16 10 18)
Historical Identification: Dreyer's precessed position is less than 0.2 arcmin south of the standard position, so the identification is certain. Although de Chéseaux discovered the cluster in the 1740's, his only publication of his discoveries was a report to the French Academy of Sciences which was more or less forgotten until Guillaume Bigourdan published a note about de Cheseaux in 1892; so Messier's discovery was independent.
Physical Information: The brighter parts of the nebula appear somewhat like a bird floating on a body of water, hence the "Swan". The brightest part of the nebula extend over 15 light years, but fainter clumps of gas cover 40 or more light years. About three dozen young stars are hidden within the gas and dust of the nebula, which has nearly a thousand solar masses of gas thinly spread over its volume. The Swan is about 5700 light years from the Sun. Apparent size 20 by 15 arcmin.
NOAO image of emission nebula and open cluster NGC 6618, also known as M17, or the Swan Nebula
Above, a ? arcmin wide image of NGC 6618 (Image Credit Adam Block/NOAO/AURA/NSF/NOAO)
Below, a ? arcmin wide multi-spectral image of the Swan reveals more detail (Image Credit ESO)
ESO multi-spectral image of emission nebula and open cluster NGC 6618, also known as M17, or the Swan Nebula
Below, a ? arcmin wide image of M17 (Image Credit and © Jim Misti, Misti Mountain Observatory; used by permission)
Misti Mountain Observatory image of emission nebula and open cluster NGC 6618, also known as M17, or the Swan Nebula
Below, a ? arcmin wide multi-spectral image reveals features hidden in visible light
(Image Credit ESO/INAF-VST/OmegaCAM. Acknowledgement: OmegaCen/Astro-WISE/Kapteyn Institute)
Wide-field ESO multi-spectral image of emission nebula and open cluster NGC 6618, also known as M17, or the Swan Nebula

NGC 6619 (= PGC 61721)
Discovered (Jun 6, 1864) by
Albert Marth (376)
A 13th-magnitude elliptical galaxy (type E1?) in Hercules (RA 18 18 55.5, Dec +23 39 19)
Historical Identification:
Physical Information: Apparent size 1.2 by 1.1? arcmin

NGC 6620
Discovered (Sep 3, 1880) by
Edward Pickering (HN 43)
A 13th-magnitude planetary nebula in Sagittarius (RA 18 22 54.2, Dec -26 49 16)
Historical Identification:
Physical Information: Apparent size 0.13? arcmin

NGC 6621 (= PGC 61579, and with
NGC 6622 = Arp 81)
Discovered (Jun 2, 1885) by Lewis Swift
A magnitude 15.0 spiral galaxy (type (R)SBa? pec) in Draco (RA 18 12 59.9, Dec +68 21 15)
Historical Identification: Per Dreyer, NGC 6621 (Swift list I (#96) and II (#65?), 1860 RA 18 13 53, NPD 21 43.9) is "pretty faint, pretty small, round, a little brighter middle, southern of 2". (Note: Swift's positions for I-95/96 and II-66/65 are different, but the descriptions and relative positions are the same, so odds are Dreyer was correct in assuming they are the same objects; however, I will revisit this in a day or two, so check back then if you really care.)
Warning: Although Dreyer specifies that NGC 6621 is the southern member of the pair of galaxies, most references misidentify it as the northern member, presumably because that is the western member of the pair.
Physical Information: NGC 6621 is obviously colliding and interacting with NGC 6622, which see for images and a detailed discussion of the system.

NGC 6622 (= PGC 61582, and with
NGC 6621 = Arp 81)
Discovered (Jun 2, 1885) by Edward Swift
A magnitude 13.6 spiral galaxy (type Sb? pec) in Draco (RA 18 12 55.6, Dec +68 21 47)
Historical Identification: Per Dreyer, NGC 6622 (Swift list I (#95) and II (#66?), 1860 RA 18 13 53, NPD 21 43.7) is "pretty faint, pretty small, round, a little brighter middle, northern of 2". (Note: Swift's positions for I-95/96 and II-66/65 are different, but the descriptions and relative positions are the same, so odds are Dreyer was correct in assuming they are the same objects; however, I will revisit this in a day or two, so check back then if you really care.)
Warning: Although Dreyer specifies that NGC 6622 is the northern member of the pair of galaxies, most references misidentify it as the southern member, presumably because that is the eastern member of the pair.
Physical Information: Based on a recessional velocity of 6190 km/sec, NGC 6622 is about 290 million light years away. However, it is colliding and interacting with NGC 6621, whose recessional velocity of 6465 km/sec implies a distance of 300 million light years. The galaxies obviously cannot be at different distances, so it is probably best to say that the pair is about 295 million light years away, give or take a few million light years' uncertainty. Given that, NGC 6622's apparent size of 1.7 by 1.0 arcmin corresponds to 145 thousand light years, NGC 6621's apparent size of 0.85 by 0.65 arcmin corresponds to 75 thousand light years, and the overall dimensions of the system (about 2.15 by 1.0 arcmin) correspond to 185 thousand light years. Used by the Arp Atlas as an example of a spiral galaxy (NGC 6622) with a high brightness companion (NGC 6621).
Mount Lemmon SkyCenter image of region near interacting spiral galaxies NGC 6621 and 6622, also known as Arp 81
Above, a 12 arcmin wide image centered on NGC 6621 and 6622
(Image Credit & © above and below Adam Block, Mount Lemmon SkyCenter, University of Arizona; used by permission)
Below, a 2.4 arcmin wide image of the pair of interacting galaxies
Mount Lemmon SkyCenter image of interacting spiral galaxies NGC 6621 and 6622, also known as Arp 81
Below, a ? arcmin wide HST image of the pair (slightly rotated to allow for greater detail)
(Image Credit NASA, ESA, Hubble Heritage (STScI/AURA)-ESA, W. Keel (Univ. Alabama, Tuscaloosa))
HST image of interacting spiral galaxies NGC 6621 and 6622, also known as Arp 81
Below, a ? arcmin wide image of Arp 81 (Image Credit Hubble Legacy Archive; processing by Martin Pugh)HST image of interacting spiral galaxies NGC 6621 and 6622, also known as Arp 81; post-processing by Martin Pugh to bring out greater detail

NGC 6623 (= PGC 61739)
Discovered (Jun 6, 1864) by
Albert Marth (377)
A 13th-magnitude elliptical galaxy (type E1?) in Hercules (RA 18 19 42.9, Dec +23 42 34)
Historical Identification: Its companion is too faint to have been noticed by Marth, so the NGC designation applies only to the brighter galaxy.
Physical Information: Apparent size 1.3 by 1.2? arcmin. Recessional velocity 4845 km/sec. Apparently involved with PGC 61744, which is superimposed on it and has an essentially identical recessional velocity.

PGC 61744
Not an NGC object, but listed here since probably paired with
NGC 6623
A 15th-magnitude compact galaxy (type C??) in Hercules (RA 18 19 42.7, Dec +23 42 07)
Physical Information: Apparent size 0.15 by 0.15? arcmin. Recessional velocity 4940 km/sec. Apparently involved with NGC 6623, which is superimposed on it and has an essentially identical recessional velocity. Misidentified in Steinicke as PGC 61749.

NGC 6624 (= GCL 93)
Discovered (Jun 24, 1784) by
William Herschel
An 8th-magnitude globular cluster (type VI) in Sagittarius (RA 18 23 40.5, Dec -30 21 38)
Historical Identification:
Physical Information: Apparent size 8.8? arcmin

NGC 6625 (= OCL 58)
Discovered (Jul 31, 1826) by
John Herschel
A 9th-magnitude open cluster in Scutum (RA 18 23 12.8, Dec -12 00 47)
Historical Identification:
Physical Information: Apparent size 39? arcmin

NGC 6626 (=
M28 = GCL 94)
Discovered (Jul 27, 1764) by Charles Messier (and listed as M28)
A 7th-magnitude globular cluster (type IV) in Sagittarius (RA 18 24 32.9, Dec -24 52 10)
Historical Identification:
Physical Information: About 80 light years across, and 18 thousand light years away. Apparent size 13.8? arcmin.
NOAO image of globular cluster NGC 6626, also known as M28
Above, a ? arcmin wide image of NGC 6626 (Image Credits: AURA, NSF, NOAO)
Below, a ? arcmin wide view of the cluster
(Image Credit & © Jim Misti, Misti Mountain Observatory; used by permission)
Misti Mountain Observatory image of globular cluster NGC 6626, also known as M28

NGC 6627 (= PGC 61792)
Discovered (Jul 13, 1863) by
Albert Marth (378)
A 13th-magnitude spiral galaxy (type SBb?) in Hercules (RA 18 22 38.9, Dec +15 41 54)
Historical Identification:
Physical Information: Apparent size 1.3 by 1.2? arcmin

NGC 6628 (= PGC 61790)
Discovered (Jun 6, 1864) by
Albert Marth (379)
A 13th-magnitude lenticular galaxy (type S0?) in Hercules (RA 18 22 21.7, Dec +23 28 39)
Historical Identification:
Physical Information: Apparent size 1.9 by 1.3? arcmin

NGC 6629
Discovered (Aug 7, 1784) by
William Herschel
An 11th-magnitude planetary nebula in Sagittarius (RA 18 25 42.4, Dec -23 12 08)
Historical Identification:
Physical Information: Apparent size 0.4 by 0.35 arcmin.
HST image of NGC 6629 superimposed on a DSS image of the region near the planetary nebula
Below, a 12 arcmin wide DSS image centered on NGC 6629 (Hubble Legacy Archive image superimposed)
Below, a 2.4 arcmin wide HST/DSS composite image of the planetary nebula
HST image of planetary nebula NGC 6629 superimposed on a DSS image
Below, a ? arcmin wide image of the planetary nebula (Image Credit Hubble Legacy Archive)
HST image of planetary nebula NGC 6629

NGC 6630 (= PGC 62008)
Discovered (Jun 8, 1836) by
John Herschel
A 14th-magnitude lenticular galaxy (type E/S0?) in Pavo (RA 18 32 34.5, Dec -63 17 31)
Historical Identification:
Physical Information: Apparent size 0.8 by 0.7? arcmin

NGC 6631 (= OCL 59)
Discovered (Jul 12, 1836) by
John Herschel
A 12th-magnitude open cluster (type II2m) in Scutum (RA 18 27 09.5, Dec -12 01 35)
Historical Identification:
Physical Information: Apparent size 7.0? arcmin

NGC 6632 (= PGC 61849)
Discovered (Jun 24, 1864) by
Albert Marth (380)
A 12th-magnitude spiral galaxy (type Sbc?) in Hercules (RA 18 25 03.1, Dec +27 32 09)
Historical Identification:
Physical Information: Apparent size 3.0 by 1.4? arcmin

NGC 6633 (= OCL 90)
Discovered (1745) by
Phillipe de Cheseaux
Discovered (Jul 31, 1783) by Caroline Herschel
A 5th-magnitude open cluster in Ophiuchus (RA 18 27 15.1, Dec +06 30 30)
Historical Identification: Per Dreyer, NGC 6633 (= John Herschel's GC 4410, Caroline Herschel, 1860 RA 18 20 43, NPD 83 31.3) is a "cluster, a little compressed, large star". Although de Chéseaux discovered the cluster in the 1740's, his only publication of his discoveries was a report to the French Academy of Sciences which was more or less forgotten until Guillaume Bigourdan published a note about de Cheseaux in 1892; so Dreyer had no way of knowing that Caroline Herschel was not the first to see the object. The position precesses to RA 18 27 32.0, Dec +06 33 37, about 3 arcmin northeast of the position listed above, but well within the boundary of the cluster, and "large star" almost certainly refers to 6th-magnitude HD 170200, which is on the southeast periphery of the field; so the identification is certain.
Physical Information: The cluster contains a couple of dozen relatively bright stars scattered across an irregularly shaped 20 to 30 arcmin wide field, the brightest being about magnitude 7 1/2. At the cluster's estimated distance of a thousand light years, its apparent size corresponds to about 8 light years. Based on the spectral types of its Main Sequence stars, NGC 6633's age is estimated at six to seven hundred million years.
DSS image of region near open cluster NGC 6633
Above, a 45 arcmin wide DSS image centered on NGC 6633
Below, a 30 arcmin wide DSS image of the cluster
DSS image of open cluster NGC 6633

NGC 6634
Discovered (1751) by
Nicolas Lacaille
A group of stars in Sagittarius (RA 18 29 55.3, Dec -33 30 40)
Historical Identification: Per Dreyer, NGC 6634 (= Lacaille list I #11, 1860 RA 18 20 45, NPD 123 30.5) is a "nebula, without stars". The object is now identified as a group of stars without nebulosity, showing the difficulty of determining the nature of faint fuzzy objects with visual observations through a small telescope. (Steinicke notes "not M69". This refers to the fact that Messier was looking for Lacaille's nebula when he found M69, and thought he had rediscovered the same object, as M69 looks nebular in a small telescope; but they are not the same object at all.) The position precesses to RA 18 29 58.2, Dec -33 25 20, about 5 arcmin north of the listed position; but there is nothing else nearby, so the identification is reasonably certain.
Physical Information: NGC 6634 consists of less than half a dozen stars ranging from 7th to 9th magnitude, and would have hardly seemed worth mentioning if its true nature had been more readily apparent to Lacaille.
DSS image of region near the group of stars listed as NGC 6634
Above, a 15 arcmin wide DSS image centered on NGC 6634

NGC 6635 (= PGC 61900)
Discovered (Jul 9, 1863) by
Albert Marth (381)
A 13th-magnitude lenticular galaxy (type S0?) in Hercules (RA 18 27 37.0, Dec +14 49 07)
Historical Identification:
Physical Information: Apparent size 1.0 by 0.9? arcmin

NGC 6636 (= PGC 61782 (+ PGC 61780?))
Discovered (Jul 23, 1884) by
Lewis Swift (4-68)
A pair of spiral galaxies in Draco
PGC 61782: A 14th-magnitude spiral galaxy (type Sc?) at RA 18 22 02.6, Dec +66 37 03
PGC 61780: A 15th-magnitude spiral galaxy (type Sab?) at RA 18 22 04.9, Dec +66 37 21
Historical Identification:
Physical Information: PGC 61782: Apparent size 2.1 by 0.3? arcmin. PGC 61780: Apparent size 0.3 by 0.3? arcmin. PGC 61780 recessional velocity = 4655 km/sec. PGC 61782 recessional velocity = 4393 km/sec. The difference is within the normal range of peculiar (non-Hubble expansion) velocities, so the galaxies are probably a physical pair. PGC 61780 is much smaller and fainter than PGC 61782, so its existence had little if anything to do with Swift's observation; but since it is a physical pair with the larger galaxy, it is often listed as if a part of NGC 6636.
DSS image of region near spiral galaxy NGC 6636 and its smaller companion, spiral galaxy PGC 61780
Above, a 12 arcmin DSS image centered on NGC 6636 and its companion, PGC 61780
Below, a 2.4 arcmin wide DSS image of the pair
DSS image of spiral galaxy NGC 6636 and its smaller companion, spiral galaxy PGC 61780

NGC 6637 (=
M69 = GCL 69)
Discovered (Aug 31, 1780) by Charles Messier (and listed as M69)
An 8th-magnitude globular cluster (type V) in Sagittarius (RA 18 31 23.2, Dec -32 20 51)
Historical Identification:
Physical Information: M69 is about 30 thousand light years away. Given that, its 7.1 arcmin apparent size corresponds to about 50 light years. It is said to be one of the most metal-rich of all globular clusters, suggesting a slightly younger age than is typical for such ancient objects; but its stars still have far fewer "metal" atoms (that is, atoms other than hydrogen and helium) than much younger stars like our Sun.
Composite of NOAO and DSS images of region near globular cluster NGC 6637, also known as M69
Above, a 12 arcmin wide image centered on NGC 6637 (Composite of the NOAO image below, and a DSS image)
Below, a roughly 6 arcmin wide image of the cluster (Image Credits: REU program, AURA, NSF, NOAO)
NOAO image of globular cluster NGC 6637, also known as M69
Below, a 3.5 arcmin wide detail of the cluster's core (Image Credit ESA/HST (Wikisky cutout))
HST image of the core of globular cluster NGC 6637, also known as M69

NGC 6638 (= GCL 95)
Discovered (Jul 12, 1784) by
William Herschel
A 9th-magnitude globular cluster (type VI) in Sagittarius (RA 18 30 56.2, Dec -25 29 45)
Historical Identification:
Physical Information: Apparent size 7.3? arcmin

NGC 6639 (= OCL 57)
Discovered (Jul 31, 1826) by
John Herschel
An open cluster in Scutum (RA 18 30 57.8, Dec -13 10 14)
Historical Identification:
Physical Information: Apparent size 5.0? arcmin

NGC 6640 (= PGC 61913)
Discovered (Aug 21, 1884) by
Édouard Stephan (13b-89)
A 14th-magnitude spiral galaxy (type Sc?) in Lyra (RA 18 28 08.1, Dec +34 18 09)
Historical Identification:
Physical Information: Apparent size 1.1 by 0.8? arcmin

NGC 6641 (= PGC 61935)
Discovered (Aug 9, 1866) by
Truman Safford (47)
A 13th-magnitude spiral galaxy (type S??) in Hercules (RA 18 28 57.3, Dec +22 54 12)
Historical Identification:
Physical Information: Apparent size 0.9 by 0.7? arcmin

NGC 6642 (= GCL 97)
Discovered (Aug 7, 1784) by
William Herschel
A 9th-magnitude globular cluster (type IV) in Sagittarius (RA 18 31 54.3, Dec -23 28 33)
Historical Identification:
Physical Information: Apparent size 5.8? arcmin

NGC 6643 (= PGC 61742)
Discovered (1858) by
Eduard Schönfeld (BD +74 766)
An 11th-magnitude spiral galaxy (type Sc?) in Draco (RA 18 19 45.6, Dec +74 34 06)
Historical Identification:
Physical Information: Apparent size 3.7 by 1.8? arcmin

NGC 6644
Discovered (Jul 13, 1880) by
Edward Pickering
An 11th-magnitude planetary nebula in Sagittarius (RA 18 32 34.7, Dec -25 07 42)
Historical Identification:
Physical Information: Apparent size 0.2? arcmin

NGC 6645 (= OCL 48)
Discovered (Jun 27, 1786) by
William Herschel
A 9th-magnitude open cluster (type III1m) in Sagittarius (RA 18 32 37.8, Dec -16 53 02)
Historical Identification:
Physical Information: Apparent size 15? arcmin

NGC 6646 (= PGC 61944)
Discovered (Jun 26, 1802) by
William Herschel
A 13th-magnitude spiral galaxy (type Sa?) in Lyra (RA 18 29 38.7, Dec +39 51 54)
Historical Identification:
Physical Information: Apparent size 1.6 by 1.3? arcmin

NGC 6647
Discovered (Jun 18, 1784) by
William Herschel
A 7th-magnitude open cluster in Sagittarius (RA 18 32 49.0, Dec -17 13 42)
Historical Identification:
Physical Information:

NGC 6648
Recorded (1825) by
Wilhelm Struve (7)
A pair of stars in Draco (RA 18 25 37.4, Dec +64 58 33)
Historical Identification:

NGC 6649 (= OCL 66)
Discovered (May 27, 1835) by
John Herschel
A 9th-magnitude open cluster (type II2m) in Scutum (RA 18 33 28.3, Dec -10 24 08)
Historical Identification:
Physical Information: Per Dreyer, NGC 6649 (= John Herschel's GC 4420, 1860 RA 18 25 44, NPD 100 29.5) is a "cluster, poor, a little compressed, pretty small, stars from 9th-10th and 12th-13th magnitude". Apparent size 6.0? arcmin.
DSS image of region near open cluster NGC 6649
Above, a 20 arcmin wide DSS image centered on NGC 6649
Below, a 12 arcmin wide DSS image of the cluster
DSS image of open cluster NGC 6649
Celestial Atlas
(NGC 6550 - 6599) ←     NGC Objects: NGC 6600 - 6649     → (NGC 6650 - 6699)