M68 (Hydra): 12 39 28.0 -26 44 34, Vmag 7.3, SB 12.5, size 11’, class X:
Low to the horizon at the time. Large, bright, beautiful cluster, with a bright center with many stars resolved in front of the central glow, and stars streaming out from it. The periphery stars can easily be imagined forming a spiral as if the globular was spinning like a sprinkler. 33,000 ly distant from us, it is moving towards us and it unusually placed for a globular, being in the hemisphere opposite from the galactic center.
NGC 5694 (Hydra): 14 39 36.5 -26 32 18, Vmag 10.2, SB 13.4, size 4.3’, class VII
Very small and compact in this magnification, fairly bright center, the periphery stars are mostly a non-stellar haze, but there are a few stars resolved here and there. May 22, 1784 by William Herschel, it is remote from us (144,000 ly) and he did not resolve it to stars. The cluster's apparent diameter of 3.6 minutes of arc corresponds to a linear extension of almost 120 light-years. Its apparent visual brightness of 10.17 mag corresponds to an absolute visual magnitude of -7.81, or an intrinsic luminosity of about 120,000 times that of our sun.
NGC 5824 (Lupus) 15 03 58.5 -33 04 04, Vmag 9.1, SB 13.4, size 7.4’, class I
Small, very bright center, unresolved, with very few periphery stars. 104,000 ly from us, 84,400 ly from the galactic center.
NGC 5986 (Libra): 15 46 03.5 -37 47 10, Vmag 7.6, SM 12.5, size 9.6’ class XI:
Appears as a fairly large loose glittery haze, like mica flakes in a pile of sand. Another Herschel discovery.
M5 (Serpens) 15 18 33.8 +02 04 58, Vmag 5.7, SB 12.5, size 23’, class V
What to say about this huge, bright, beautiful object? What I noticed were the loops of stars coming out from the center, and the outer periphery forming a large crescent shape. 24,400 ly from us, 20,200 from the galactic center.
M107 (Ophiuchus) 16 32 31.9 -13 03 13, Vmag 7.8, SB 13.4, size 13’, class X:
Large, very loose, with a small, intense bright central region with resolved stars intermingled, and many gangly chains of stars stretching well away from the center to the periphery. 20,900 ly from us, 10,800 ly from the galactic center, its metallicity conforms to the bulk of the halo population.
M10 (Ophiuchus) 16 57 08.9 -04 05 58, Vmag 6.1, SB 12.1, size 16’, class VI
Round center with a thin V-shaped train of stars running through it. 14,300 ly from us, 15,000 ly from the galactic center, it completes an orbit around the Milky Way galaxy about every 140 million years, during which it crosses the plane of the galactic disk every 53 million years.
M12 16 47 14.5 -01 56 52, Vmag 6.6, SB 13.1, size 20’ class IX
Similar to M10 but without the lane of stars through it. At its distance of about 16,000 light years, the apparent diameter of M12 of 16.0 arc minutes corresponds to about 75 light years. This stellar swarm is approaching us at 16 km/sec. Located 2 deg N and 2 deg W of M10.
NGC 6235 (Ophiuchus) 17 17 59.2 -23 45 57, Vmag 8.9, SB 12.4, size 5’, class X
Fairly large, little central concentration, loose periphery. Distance from Sun: 37,500 ly, distance from galactic center: 13,700 ly
NGC 6287 (Ophiuchus) 17 05 09.4 -22 42 29, Vmag 9.3, SB 12.7, 4.8’, class VII
Fainter and smaller than nearby NGC 6235, larger and brighter center, with resolved stars mixed with the finer haze, and noticeable concentration of stars like ears on either side of the periphery. Distance from sun 30,600 ly. distance from Galactic Center: 6,800 ly
NGC 6284 (Ophiuchus) 17 04 28.8 -24 45 53, Vmag 8.9, SB 12.9, size 6.2’, class IX
Very bright round center and a multitude of stars in the round periphery. Distance from Sun 43,000 ly, distance from Galactic Center 24,400 ly. A recent study indicates NGC 6284 is a post-core collapse (PCC) cluster. The nearby metal-poor star HD 194598 [es] may be a recent runaway from NGC 6284.
NGC 6325 (Ophiuchus) 16 53 25.4 -22 10 38, Vmag 10.2, SB 13.3, size 4.1’, class IV
Faint, loose scattered periphery, with a moderately concentrated bright center.
M14 (Ophiuchus): 17 37 36.1 -03 14 45, Vmag 7.6, SB 12.8, size 11’, class VIII
Very bright and grainy with stars, evenly bright, elliptical shaped. About 100 ly across and about 30,000 ly away. Several hundred thousand stars.
NGC 6366 (Ophiuchus): 17 27 44.3 -05 04 36, Vmag 9.5, SB 15.1, size 13’, class XI
Loose, even magnitude stars, very open cluster like, it lies 0.5-degree east of 4.5-mag star 47 and has two thicker horns of stars which remind my of a Texas longhorn. NGC 6366 is quite faint and weakly concentrated. As its brightest stars are only of magnitude 13.6, larger telescopes are required to view them; the horizontal branch giants are of magnitude 15.7. The overall visual magnitude of 9.2, at its distance of 11,700 light years and taking into account the interstellar absorption in its direction, gives an absolute visual brightness of -5.77 magnitudes, or a luminosity of only about 20,000 times that of our sun. Compared to other globular clusters, the cluster is rather rich in elements heavier than Helium. NGC 6366 is approaching us at 122 km/s.
IC 1257 (Ophiuchus) 17 27 08.0 -07 05 36, Vmag 13.1, SB 14.3, size 1.7’,
Small, faint, non-stellar, needed finder to locate and see it. IC 1257 is at a distance of 81,500 light years from our Sun and about 58,400 light years from the Galactic Center. It is approaching us at about 140 km/sec, and it is a highly reddened globular cluster well beyond the Galactic center.
NGC 6426 (Ophiuchus): 17 44 54.7 +03 10 13, Vmag 10.9, SB 14, size 4.2’, class IX
Faint, rather small, the center is a grey dot with a faint round haze around it. 67,200 ly from the sung, 46,900 ly from the galactic center.
NGC 6539 (Ophiuchus) 18 04 49.8 -07 35 09, Vmag 10.1, SB 13.1, size 4’, class X
Bright, loose, with a stream of (probably) foreground stars running through it. This cluster is located in the outer parts of the Galactic bulge. There is a large dark cloud complex located in the fore of this cluster, causing reddening from extinction. Compared to other globular clusters, NGC 6539 is considered metal rich, indicating that it has a relatively higher abundance of elements more massive than helium. Distance from Sun 25,400 ly, distance from Galactic Center 9,800 ly.
NGC 6517 (Ophiuchus) 18 01 50.6 -08 57 32, Vmag 8.9, SB 13.4, size 7.9’ class IV
Bright, compact core, with an irregularly round spray of stars around it, nearly triangular. Distance from Sun: 34,600 ly, Distance from Galactic Center 13,700 ly
NGC 6535 (Ophiuchus): 18 03 50.7 -00 17 49, Vmag 9.3, SB 12, size 3.4’, class XI
Small, faint, loose, open cluster like. Distance from Sun: 22,200 ly. Distance from Galactic Center:
12,700 ly
NGC 6293 (Ophiuchus) 17 10 10.4 -26 34 54, Vmag 8.3, SB 12.9, size 8.2’ IV
Small bright stellar core, round, with field star to the side. Distance from Sun: 31,000 ly. Distance from Galactic Center: 6,200 ly
M19 (Ophiuchus) 17 02 37.7 -26 16 05, Vmag 6.8, SB 13, size 17’, class VII
Very bright, stellar core and a myriad of stars around it which form an overall oval shape. Shapley found it at ellipticity 6, corresponding E4, elongated at position angle 15 deg. He estimated that there could be counted twice as many stars along the major axis as along the minor. This deformation of the cluster from the globular shape may have to do with its proximity to the Galactic Center: While about 28,000 light years away from our Solar System, it is quite near to the Galactic Center, only about 5,200 light years away. It is located nine degrees above the galactic plane (i.e., at a galactic latitude of 9 deg North) and slightly west og the Galactic Center, as seen from Earth; it is perhaps very slightly more remote from us than the center of the Milky Way. M19 is receding from us at 146 km/sec. At its distance, its diameter of 17 arc minutes corresponds to a linear one of about 140 light years along the major axis, and its absolute magnitude is about -9 Mag. In amateur instruments it appears smaller, perhaps about 6' visually and 13.5' photographically - still corresponding to a linear diameter of 110 light years.
NGC 6355 (Ophiuchus) 17 23 58.6 -26 21 13, Vmag 8.6, size 4.2’
Stellar core with faint scattered periphery of evenly bright stars, with a very pretty streams of bright stars bracketing it to the east and west. Distance from Sun: 30,000 kly. Distance from Galactic Center: 4,600 ly
M62 (Ophiuchus) 17 01 12.6 -30 06 44, Vmag 6.4. SB 12.3, size 15’, class IV.
Bright, large, uniformly resolved, with the "center" slightly off center to the SE. Several prominent arms of stars reaching out from it. M62 is one of the closest of Messier's globulars to the Galactic center (only about 6100 light years), so that it is deformed by tidal forces. M62 appears at a diameter of 15 arc minutes, about half of the Full Moon, corresponding to a linear extension of about 100 light-years.
NGC 6304 (Ophiuchus) 17 14 32.5 -29 27 44, Vmag 8.3, SB 12.8, size 8’, class VI
Rough and mottled central region which seems broken to three sections. Large, chaotic periphery of stars. Distance from Sun: 19,200 ly. Distance from Galactic Center: 7,500 ly.
NGC 6316 (Ophiuchus) 17 16 37.4 -28 08 24, Vamg 8.1, SB 11.8, size 5.4’, class III
Small, compact, evenly bright and resolved from center to periphery. NGC 6316 has a metallicity of -0.45;[4] this means that its ratio of hydrogen/helium to other elements is only 35% that of the Sun, but still enough to be considered a "metal-rich" globular cluster. Distance from Sun: 33,900 ly, Distance from Galactic Center 8,500 ly.
M9 (Ophiuchus) 17 19 11.8 -18 30 59, Vmag 7.8, SB 13.2, size 12', class VIII
Bright, rather compact, slightly out of round, intensely packed with stars from the periphery to the center, bounded to the SW by large dark nebula.
M9 is one of the nearer globular clusters to the nucleus of our Galaxy, with a computed distance of 5500 light-years from the Galactic Center (Burnham gives 7500, a slightly too high value). Its 12.0 arc minutes angular diameter corresponds to a linear extension of 90 light years at its distance of about 25,800 light years from our Solar system. However, it appears somewhat smaller visually, about 3 or 4', and on conventional photos can be traced to about 9.3 arc minutes. Its light is significantly dimmed by interstellar dust, as it lies at the edge of a patch of dark nebula (Barnard 64); its light is probably weakened by at least one magnitude (a factor of about 2.5). Taking these facts into account, the apparent visual brightness of this cluster of 7.7 magnitudes corresponds to an absolute brightness of -8.04 Mag, or a luminosity of roughly 120,000 times that of our sun. Visually it appeared oval to Mallas, and the ellipticity of 9 mentioned by Shapley can be seen in our photograph also. As its concentration class VIII indicates, the stars of M9 are about intermediately compressed toward its center. M9 is receding from us at the very high velocity of 224 km/sec.
NGC 6342 (Ophiuchus) 17 21 10.2 -19 35 14, Vmag 9.5, SB 12.7, size 4.4’, class IV
Small somewhat faint, with a bright center and unevenly populated periphery. NGC 6342 lies just about 80' SE of the more prominent cluster M9, and at about the same distance, so that these clusters are probably physical neighbors. The inferior apparent size and brightness of NGC 6342 indicate that this globular is intrinsically much fainter and smaller than its prominent neighbor. Distance from Sun: 27,700 ly, Distance from Galactic Center: 5,500 ly
NGC 6356 (Ophiuchus) 17 23 35.0 -17 48 47, Vmag 8.2, SB 13.2, size 10’,
Bright, intense central region, fairly large and bright periphery, some faint thin streams of stars coming from it. NGC 6356 is situated just 80' NE of prominent Messier 9, but at roughly the double distance. The cluster is relatively metal-rich and therefore has a large amount of interstellar dust in its core. Distance from Sun: 49,200 ly, Distance from Galactic Center: 24,400 ly
NGC 6401 (Ophiuchus) 17 38 36.9 -23 54 32, Vmag 7.4, SB 8.7, size 1.8', class VIII
Bright stellar center and faint, elongated periphery, thick parenthesis-like. Thin, patchy dark nebula spotting the view N-S (these are B82, B81 which partly overlaps NGC 6401, and the darkest B83 to the south). Distance from Sun: 34,600 ly, Distance from Galactic Center: 8,800 ly
NGC 6440 (Sagittarius) 17 48 52.6 -20 21 34, Vmag 9.3, SB 12.5, size 4.4’, class V
Small very bright, concentrated. Large dark nebula cloud B280 to the SW, with darker thin E-W cloud B84 to the NW. Did not notice nearby PNe NGC 6445. Distance from Sun: 27,700 ly, Distance from Galactic Center: 4,200 ly
NGC 6144 (Scorpius) 16 27 14.1 -26 01 29, Vmag 9, SB 13.3, size 7.4',
Loose, open cluster like, with a small intense core. It's in Antares' glow (I can still see it ok with Antares in the field, but it's nicer with Antares moved out of field.) Distance from Sun: 29,000 ly, Distance from Galactic Center: 8,800 ly
M4 (Scorpius) 16 23 35.5 -26 31 31, Vmag 5.4, SB 13.2, size 36’, class XI
Very large, very loose, there is a thick bar with a backward bending wing making the relatively densest formation of stars boomerang shaped, the same size as the cluster itself.
The distance of M4 is perhaps only about 7,200 light years, which until recently, has perhaps been the smallest for a globular; the only serious competitor was NGC 6397 in the southern constellation Ara, yet that one seems to be very slightly more remote now (7,500 light-years). This changed only with the recent (2007) discovery of faint globular cluster FSR 1767 (or 2MASS-GC04) which is estimated at only 4,900 light-years. As a remarkable detail, M4 displays a central "bar" structure, well visible in our photo, roughly from slightly below left to slightly above right; this bar of 11th mag stars is about 2 1/2 ' long in position angle 12 deg and was first noted by William Herschel in 1783. It may be that this structure caused Harlow Shapley to consider it to be elongated slightly elliptically (0.9, in position angle 115 deg), a notion which cannot be confirmed in modern observations or photographs.
M4 would be one of the most splendid globulars in the sky if it were not obscured by heavy clouds of dark interstellar matter. Interstellar absorption also reddens the color of the light from the cluster, and gives it a slightly orange or brownish appearance on color images. Its angular diameter, seen on deep photographs, is about 36 minutes of arc, more than that of the Full Moon; this corresponds to a linear diameter of about 75 light years. On typical photos it appears somewhat smaller at about 26', and visually it was estimated at 14 arc minutes. Its tidal radius, determined by the distance where tidal gravitational forces of the Milky Way Galaxy would cause member stars to escape, is estimated at 32.49', or about 70 light-years, so that this globular gravitationally dominates a spherical volume 140 light-years in diameter.
M4 is one of the most open, or loose, globulars, as its classification in concentration class IX indicates. Its compressed central core was measured at 1.66' diameter, or linearly 3.6 light-years. Its half-mass radius is 3.65' or about 8 light-years, so half the cluster's mass is concentrated in an inner spherical volume of 16 light-years diameter. It is receding from us at 70.4 km/sec.
M80 (Scorpius) 16 17 02.5 -22 58 30, Vmag 7.3, SB 12.3, size 10', class II
Bright central region dense with stars, loose diffuse periphery. Its 10' angular diameter corresponds to roughly 95 light years linear dimension at its distance of 32,600 light years. This dense stellar swarm contains several 100,000s of stars, held together by their mutual gravitational attraction. It is one of the densest globulars in our Milky Way Galaxy. As was found by astronomers from observations with the Hubble Space Telescope in 1999 in the visible and UV part of the electromagnetic spectrum, M80 contains a large number of so-called "Blue Stragglers" in its core, about twice as much as any other globular investigated with the HST. These stars are blue and bright stars which appear near the main-sequence of the Hertzsprung-Russell diagram, and thus appear more massive and younger than the globular clusters age. The reason is very probably that these stars lost their cooler envelopes in close encounters with other stars. Their large number in M80 indicates an exceptionally high stellar collision rate in the core of this globular cluster.
NGC 6139 (Scorpius) 16 27 40.4 -38 50 56, Vmag 9.1, SB 13.7, size 8.2', class II
Small bright compact center, loose periphery of stars. Distance from Sun: 32,900 ly, Distance from Galactic Center: 11,700 ly
NGC 6256 (Scorpius) 16 59 32.6 -37 07 17, Vmag 11.3, SB 14.4, size 4.1'
Small, relatively faint, small stellar center, hazy periphery of stars which resolves to stars with longer attention, more stars to the south of center. Distance from Sun: 33,600 ly, Distance from Galactic Center: 9,800 ly
NGC 6388 (Scorpius) 17 36 17.0 -44 44 06, Vmag 6.8, SB 11.9, size 10.4’, class III
Intensely bright central region peppered with stars, diffuse large periphery of stars spreading out. I forgot to switch to a Ha filter, since this cluster boarders part of the Dragon Heart nebula. Distance from Sun: 32,300 ly Distance from Galactic Center: 10,100 ly
NGC 6496 (Corona Australis) 17:59:03 -44:15:57.4, Vmag 8.5, size 5.3'
Fairly large, faint, very loose and open cluster like, mostly similar magnitude stars in an irregularly round center region and loose and jangly periphery. Distance from Sun: 36,800 ly, Distance from Galactic Center: 13,700 ly
NGC 6541 (Corona Australis) 18 08 02.2 -43 42 20, Vmag, 6.3, SB 12.2, size 15’, class III
Bright concentrated center peppered with resolved stars, loose peripheral extensions in the halo, moderately sized. Distance from Sun: 24,400 ly, Distance from Galactic Center: 6,800 ly
NGC 6380 (Corona Australis) 17 34 28.0 -39 04 09, Vmag 11.5, SB 14.3, size 3.6’
Small glowing center, almost fan shaped, with a bright star at the southern edge of the center. The halo stars form an expanding glittery haze. =Tonantzintla 1. NGC 6380 was thought to be just an open cluster. In the 1950s, this object was found to be globular by A.D. Thackeray on photographic plates obtained with the 74-inch telescope at Radcliffe Observatory. It was independently discovered once more by Paris Pismis, who cataloged it as Tonantzintla 1. Distance from Sun: 35,500 ly, Distance from Galactic Center: 10,800 ly
NGC 6441 (Scorpius) 17 50 12.9 -37 03 04, Vmag 7.2, SB 12.1, size 9.6’, class III
Very bright core and spikey halo, near bright star G Sco. Distance from Sun: 37,800 ly, Distance from Galactic Center: 12,700 ly. NGC 6441 hosts a planetary nebula, which was not seen.
NGC 6453 (Scorpius) 17 50 51.8 -34 35 55, Vmag 10.2, SB 14.6, size 7.6’, class IV
Small, faint, resolved to its small center with delicate sprays of stars to its halo. Distance from Sun:
37,800 ly, Distance from Galactic Center: 12,100 ly
NGC 6522 (Sagittarius) 18 03 35.0 -30 02 02, Vmag 9.9, SB 14.8, size 9.4’, class VI, Distance from Sun: 25,100 ly, Distance from Galactic Center: 2,000 ly
NGC 6528 (Sagittarius) 18 04 49.6 -30 03 21 Vmag 9.6, SB 13.1, size 5’, class V, Distance from Sun:
25,800 ly, Distance from Galactic Center: 2,000 kly
In the same FOV, they appear as drops from the tip of the Sagittarius teapot's spout. Very similar in appearance, 6522 is slightly larger than the other and with a bit looser halo, still with a concentrated center. 6528 is smaller, with a very concentrated center. In the same FOV, which is intensely dense with stars (being in Baade's Window).
NGC 6558 (Sagittarius)18 10 17.6 -31 45 47, Vmag 8.6, size 4.2’
Small and concentrated, open cluster like halo, bright stellar core off center slightly to north. Very rich field. Distance from Sun: 24,100 ly, Distance from Galactic Center: 3,300 ly
NGC 6569 (Sagittarius) 18 13 38.9 -31 49 35, Vmag 8.4, SB 12.4, size 6.4', class VIII
Fairly large, faint, the halo is an even magnitude spray of stars, the center is not well concentrated with some stars resolved. Lies within dark nebula B305. Distance from Sun: 35,500 ly, Distance from Galactic Center: 10,100 ly
NGC 6624 (Sagittarius) 18 23 40.5 -30 21 40, Vmag 7.6, SB 12.3, size 8.8', class VI
Intensely bright, grainy resolved core with stellar nucleus, and loose uneven spray of halo stars, fairly large. Distance from Sun: 25,800 ly, Distance from Galactic Center: 3,900 ly
NGC 6544 (Sagittarius) 18 07 20.6 -24 59 51, Vmag 7.5, SB 12.3, size 9.2'
Bright center, diffuse and irregularly shaped halo. It appears to be embedded in large open cluster of stars spreading from the halo to the SW, but this is likely just the very rich field. M8 Lagoon Nebula to the NW. Distance from Sun: 9,800 ly, Distance from Galactic Center: 16,600 ly
NGC 6553 (Sagittarius) 18 09 17.3 -25 54 28, Vmag 8.3. SB 13.1, size 9.2', class XI
Large, bright, evenly spread resolved stars to core, round, in a very dense field. Distance from Sun:
19,600 ly, Distance from Galactic Center: 7,200 ly
NGC 6540 (Sagittarius) 18 06 08.6 -27 45 44, Vmag 14.6, SB 15.5, size 1.5’
Small bright concentration of stars, some of which are resolved, very like an open cluster, in an intensely dense field =Djorg 3, NGC 6540 was discovered by William Herschel in 1784 and cataloged as H II.198. While Herschel classified it as a "faint nebula," indicated by his classification in the second group of deepsky objects, this object was longly listed as open cluster, e.g. by Collinder who designated it Cr 364. S. Djorgovski independently "rediscovered" it in September 1986 without noting its identity, when looking for obscured globular clusters in the IRAS Point Source Catalog, labeled it Djorg 3, and suspected it to be a globular cluster (Djorgovski 1987). It was finaly Bica et.al. (1994) who identified it with the NGC object and confirmed its nature as a globular cluster.
ESO 456-38 (Sagittarius) 18 01 49.1 -27 49 33, Vmag 9.9, SB 14.9, size 9.9'
Moderately small concentration of slightly brighter (but still rather faint) stars very slightly separated from the very dense field. Easily mistaken for an open cluster. From a recent paper's abstract: "The object ESO 456-SC38 (Djorgovski 2) is one of the globular clusters that is closest to the Galactic center. It is on the blue horizontal branch and has a moderate metallicity of [Fe/H] ∼ −1.0. It is thus similar to the very old inner bulge globular clusters NGC 6522, NGC 6558, and HP 1, and therefore appears to be part of the primeval formation stages of the Milky Way." Distance from Sun: 20,500 ly, Distance from Galactic Center: 5,900 ly
M22 (Sagittarius) 18 36 24.2 -23 54 12, Vmag 5.2, SB 12.7, size 32’, class VII
What is to say? Stunning, as always.
At 10,400 light years, it is one of the nearer globular clusters. At this distance, its 32' angular diameter, sligtly larger than that of the Full Moon, corresponds to a linear of about 97 light years; visually, it is still about 17'. It is visible to the naked eye for observers at not too northern latitudes, as it is brighter than the Hercules globular cluster M13 and outshined only by the two bright southern globulars (not in Messier's catalog), Omega Centauri (NGC 5139) and 47 Tucanae (NGC 104) - this is the ranking of the four brightest in the sky.
While Shapley and Pease counted 70,000 stars in this great stellar swarm, only the relatively small number of 32 variables has been identified, half of them already known to Bailey in 1902, among them a long-period Mira variable which is probably not a member. The brightest stars are about mag 11. The stars are spread over a region roughly 200 light years in diameter, and receding from us at about 149 km/sec.
This cluster is notable because it contains a weak planetary nebula, discovered by the infrared satellite IRAS and cataloged as IRAS 18333-2357 or GJJC 1. This planetary was the second discovered in a globular cluster after Pease 1 in M15, and one of only four known planetary nebula in Milky Way globular clusters.
Recent Hubble Space Telescope investigations of M22 have led to the discovery of a considerable number of planet-sized objects which appear to float through this globular cluster; these objects may have masses of only 80 times that of Earth, and were discovered by so-called micro lensing effects, i.e. bending of light of background member stars of the cluster.
M28 (Sagittarius) 18 24 32.9 -24 52 12, Vmag 6.9, SB 12.6, size 13.8', class IV
Very bright central concentration which still has many stars resolved in it, and a very large diffuse halo of stars. Around half the size of nearby M22. At about 18,000 to 19,000 light years distance, M28 with its linear diameter of 60 light years appears considerably smaller and more compressed than its more impressive neighbor, M22. It is slightly elliptical shaped according to H. Shapley. To resolve it into stars, larger instruments are required; it was William Herschel who first described it as a "star cloud".
NGC 6638 (Sagittarius) 18 30 56.2 -25 29 47, Vmag 9.2, SB 13.5, size 7.3’, class VI
Small, bright and compact, with diffuse halo spray of stars, in a very rich field. Distance from Sun:
30,600 ly, Distance from Galactic Center: 7,200 ly
NGC 6642 (Sagittarius) 18 31 54.3 -23 28 35, Vmag 8.9, SB 12.7, size 5.8’,
Bright and compact, pretty well resolved, with five prominent arms coming from it looking like a starfish. Distance from Sun: 26,400 ly, Distance from Galactic Center: 5,500 ly
M69 (Sagittarius) 18 31 23.2 -32 20 53, Vmag 7.7, SB 12.7, 9.8’, class V
Bright and small core, many stars resolved. Distinctive line of N-S stars to the west in the field.
M69 is only 7.1 arc minutes in diameter in long exposure photos, corresponding to roughly 61 light years at its 29,700 light years distance. Very deep photos show that it is somewhat more extended: 9.8 arc minutes, or linearly, about 85 light years. The visually bright compact core is less than half, only about 3'. As M69 is quite close to the Galactic Center (only about 6,200 light-years distant), its tidal gravitational radius is comparatively small, 8.35' or 72 light years. Its stellar concentration is about average for a globular cluster, as it is of concentration class V. Its central core has a diameter of 0.68' or roughly 6 light years, while its half-mass radius is 0.83' or about 7.2 light years.
M69's spectral type has been determined as G2 or G3, and its color index is B-V = 1.01. It is one of the metal-richest globulars, meaning that its stars show a relatively high abundance of elements heavier than Helium. Nevertheless, this value is still significantly lower than that for the younger (Population I) stars like our Sun, indicating that even this globular was formed at early cosmic times when the universe contained less heavier elements, as these elements still had to be formed in the stars.
The distance of M69, about 29,700 light years, is roughly the same as that of its apparent neighbor, M70 which is at about 29,400 light years. This indicates that these two globulars happen to be physically neighbored; their mutual distance can be calculated to be as small as about 1,800 light years. In contrast, the also apparently nearby situated globular M54 is about three times as distant.
M70 (Sagittarius) 18 43 12.7 -32 17 31, Vmag 7.8, SB 12.3, size 8’, class V
Small bright, many stars resolved. Short line of three similar magnitude stars sprout from its NW side.
M70 is 8.0 arc minutes in apparent angular and roughly 68 light years in linear diameter, its bright visual core being only about 4'. It is rapidly receding from us, at about 200 km/sec. Only 2 variables are known in this stellar swarm. The core of M70 is of extreme density, as it has undergone a core collapse somewhen in its history, similar to at least 21 and perhaps up to 29 of the 150 known Milky Way globulars, including M15, M30, and possibly M62 and M79. Globular cluster M70 became famous in 1995 when the great comet Hale-Bopp was discovered near it by Alan Hale and Thomas Bopp as they were observing this globular.
NGC 6652 (Sagittarius) 18 35 45.7 -32 59 25, Vmag 8.5, SB 12.4, size 6', class VI
Bright core elongated E-W, round halo with some brighter stars forming a parenthesis on the E and W sides, bracketing the central region. Distance from Sun: 32,600 ly, Distance from Galactic Center: 8,800 ly
M54 (Sagittarius) 18 55 03.3 -30 28 42, Vmag 7.7, SB 13.1, size 12’, class III
Very bright concentrated large core, diffuse halo.
Its distance, for years, was estimated to be about 50-65,000 light years. However, in 1994, the exciting discovery was made that M54 was probably not a member of our Milky Way at all, but of a newly discovered dwarf galaxy! This galaxy is now called SagDEG, for Sagittarius Dwarf Elliptical Galaxy, and one of the most recently discovered Local Group galaxies.
M54 coincides with one of two major concentrations of the SagDEG galaxy and is receding from us at a very similar velocity (about 130 km/sec). This makes it probable that M54 is within this galaxy, which was estimated at a distance of 80-90,000 light years. At this distance, M54 would be one of the most luminous known globular clusters with an absolute visual magnitude of -10.01, a brilliance of about 850,000 suns like ours, and outshined only by spectacular Omega Centauri. Also, its diameter would become as large as about 300 light years. It is about three times as distant as its two apparently close neighbors, M69 and M70. And perhaps most interesting, it would make M54 the first extragalactic globular cluster ever discovered, by Charles Messier on July 24, 1778, and thus add an extra first to Messier's list of fame.
NGC 6723 (Sagittarius) 18 59 33.2 -36 37 54, Vmag 6.8, SB 12.4, size 13', class VII
Chandelier, lovely like a fountain firework. Large, bright, with an off-center bright core, and streams of stars flowing out from it. Spectacular. Distance from Sun: 28,400 ly, Distance from Galactic Center:
8,500 ly
M55 (Sagittarius) 19 39 59.4 -30 57 44, Vmag 6.3, SB 12.7, size 19’
Large, wonderfully resolved, very loose. The core is a large hazy cloud with stars resolved in front of it. It is about 17,300 light years distant, which corresponds to a linear of about 100 light years.
M75 (Sagittarius) 20 06 04.8 -21 55 17, Vmag 8.6, SB 12.8, size 6.8', class I.
Small, bright, compact, grainy with partly resolved stars.
At a distance of about 67,500 light years, M75 is one of the more remote of Messier's globular clusters, lying well beyond the Galactic center (from which it is 47,600 light years distant). Its angular diameter of 6.6' corresponds to a linear extension of well almost 130 light years, and it is of high luminosity, perhaps about 180,000 times that of the Sun (Mag -8.55).
M71 (Sagitta) 19 53 46.1 +18 46 42, Vmag, size 7.2', class X-XI
Incredibly dense field, it appears as a knot of stars in a vast fabric of stars.
It is 13,000 light years distant. Its denser, easily visible core is only about 5 to 6 arc minutes, while in photos it has an angular diameter of about 7', corresponding to a linear extension of only 27 light years, small for a globular cluster. However, faint members have been detected out to a total diameter of 24', making it measure 90 light years. The membership of these faint stars, however, is not yet finally confirmed.
NGC 6749 (Aquila) 19 05 15.3 +01 54 03, Vmag 12.4, SB 15.4, size 4"
Small, rather faint, a density of stars, open cluster like, with a very tight center as the core. Distance from Sun: 25,800 ly, Distance from Galactic Center: 16,300 ly
NGC 6760 (Aquila) 19 11 12.1 +01 01 50, Vmag 9, SB 13.8, size 9', class X
Large and dense center, round and full of hazy and resolved stars, slowly extends to the diffuse spread of stars that is the halo. Very rich field. Distance from Sun: 24,100 ly, Distance from Galactic Center:
15,600 ly
NGC 6712 (Scutum) 18 53 04.3 -08 42 22, Vmag 8.1, SB 13.1, size 9.8', class IX
Large, very bright core is dense with resolved stars, with a likewise large diffuse halo.
At its distance of 22,500 light-years, NGC 6712's apparent diameter of 7.4 minutes of arc corresponds to a linear extension of about 50 light-years, and its visual brightness of 8.1 mag to an absolute magnitude of -7.50, or an intrinsic luminosity of about 90,000 times that of our Sun. Its overall spectral type has been determined as F9. It is approaching us at 107.5 km/s.
NGC 6934 (Delphinus) 20 34 11.6 +07 24 15, Vmag, SB 13.2, size 7.1'
Very bright core, the halo has several bright star streams coming out from the core, giving it starfish-like quality. 9.5 magnitude close to the west. Distance from Sun: 50,900 ly, Distance from Galactic Center:
41,700 ly
NGC 7006 (Delphinus) 21 01 29.5 +16 11 15, Vmag 10.6, SB 13.4, size 3.6', class I
Small, very compact round core is bright and crinkled with resolved stars, stellar nucleus, and with a very large and burst-like halo, in a very dense field. Distance from Sun: 134,300 ly, Distance from Galactic Center: 125,500 ly
M72 (Aquarius) 20 53 27.9 -12 32 13, Vmag 9.2, SB 13.3, size 6.6', class IX
Small core is peppered with resolved stars, and the NW side appears broken or cut off. Halo is diffuse and irregularly round.
M72 is one of the more remote of Messier's globular clusters: At about 53,000 light years, it lies a considerable distance beyond the Galactic Center. It is of 9th or 10th apparent magnitude, but as it is so distant it is one of the more intrinsically luminous globular cluster. However, M72 is not very concentrated (Shapley classified it as class IX); among Messier's globulars, only five are even less concentrated: M55 (class XI), M71 (class X-XI) as well as M56, M68, and M107 (class X). M72 is approaching us quite rapidly, at 255 km/sec, and has the considerable number of 49 known variables, mostly RR Lyrae stars. Its diameter is about 106 light years and appears to us under an angle of 6.6 arc minutes.
M30 (Capricornus) 21 40 22.0 -23 10 45, Vmag 6.9, SB 12.3, size 12', class V
Bright compact center, spikes of stars coming out of it
Globular cluster Messier 30, at about 26,000 light years distance and about 90 light years across and appears to us under an angular diameter of about 12.0 arc minutes. It is fairly dense. Its brightest red giant stars are about of apparent visual magnitude 12.1, its horizontal branch giants at magnitude 15.1. It is approaching us at 181.9 km/s.
The core of M30 exhibits an extremely dense stellar population, and has undergone a core collapse. Consequently, M30's core is very small in extension, only about 0.12 arc minutes (7.2 arc seconds, corresponding to a linear diameter of 0.9 light years), and its half-mass radius is 1.15 arc min (8.7 light years); half of this cluster's mass is concentrated in a spherical volume of a radius equal to the distance of Sirius from us, or 17.4 light years diameter. On the other hand, its tidal radius is large: 18.34 arc minutes, corresponding to a linear radius of 139 light years. Beyond that distance, member stars would escape simply because of the Milky Way Galaxy's tidal gravitational forces.
Despite its compressed core, close encounters of the member stars seem to have occurred comparatively rare, as it appears to contain only few X-ray binary stars, according to investigations with the Chandra X-ray Observatory satellite. These particular stellar systems are thought to form in close encounters as they occur occasionally in the denser zones of globular clusters.
M2 (Aquarius) 21 33 27.0 -00 49 12, Vmag 6.6, SB 12.6, size 16’, class II
Large, bright, resolved to the large round core core, very nice
M2 has a diameter of about 175 light-years, contains about 150,000 stars, and is one of the richer and more compact globular clusters, as its classification in density class II indicates. This cluster is of notable ellipticity (ellipticity 9, or form E1), as can be noted in our photograph; it is extended in position angle 135 deg. At about 37,500 light years (according to W.E. Harris' database), it lies well beyond the Galactic Center. Visually it is of apparent magnitude 6.5 and about 6 to 8 minutes of arc in diameter, with a bright, compressed central region of about 5'. On typical photographs it can be traced to about 12.9 arc minutes, and deep photos reveal that it extends out to a diameter of 16.0 arc minutes.
As most globular clusters, M2's central part is pretty compressed: The dense central core of globular cluster M2 is only 0.34 arc minutes or about 20 arc seconds in diameter, corresponding to a diameter of 3.7 light years. Its half-mass radius is 0.93 arc minutes (56 arc seconds, or 10 light years linearly). On the other hand, its tidal radius is large: 21.45 minutes of arc, corresponding to a radius of 233 light years beyond which member stars would escape because of tidal gravitational forces from the Milky Way Galaxy.
From its color-magnitude diagram, Halton Arp (1962) has estimated the age of M2 as about 13 billion years and to be about the same as that of globular clusters M3 and M5.
M2 is approaching us at the low velocity of 5.3 km/sec. Situated in the Galactic halo, it has been classified as an "H2" halo globular. M2 is moving on a highly excentric (e=0.76) orbit of box type, with a perigalactic distance of 23,500 light-years, which carries it out to an enormous apogalactic distance of 171,000 light-years, and up to 165,000 light-years above and below the Galactic plane.
M2 is currently out at a distance of 38.1 kly (11.69 kpc) from us and 34.4 kly (10.54 kpc) from the Galactic Center. It is orbiting the Galactic Center in a considerably large orbit with a period of about 205 Myr, reaching out to an apogalacticum of 61.1 kly (18.74 kpc) and coming very close when passing the perigalacticum at only 2.86 kly (0.88 kpc). Having passed its last apogalacticum about 130 to 135 Mly ago, and its last perigalacticum about 25 Myr ago, it is currently moving out and will reach its next apogalacticum in about 80 Myr. From fitting of its Color-Magnitude Diagram (CMD), it is estimated to be 11.7 Gyr, a half-mass rasius of 15.5 ly (4.76 pc), and from the velocity dispersion of its stars, an estimated mass of 624,000 solar masses.
NGC 7492 (Aquarius) 23 08 26.7 -15 36 41, Vmag 11.2, SB 14.3, size 4.2’, class XII
Small non stellar round haze.
NGC 7492 is one of the outlying globular clusters of our Milky Way galaxy, at its distance of about 84,000 light-years from us, and 81,200 light-years from the Galactic Center. It is one of the loosest and least compressed globular clusters and lacks a dense central core. Because of its large distance, it is difficult to be resolved into stars: The brightest stars are of visual mag 15.5, the horizontal branch giants of mag 17.6. While far out at these times, globular cluster NGC 7492 is rapidly approaching us, at about 208 km/s.
M15 (Pegasus) 21 29 58.3 +12 10 01 Vmag 6.3, SB 12.6, size 18’, class IV
Gorgeous, large and bright, very finely resolved.
At a distance of about 33,600 light years, its diameter of 18.0 arc min corresponds to a linear extension of about 175 light-years, and its total visual brightness of 6.2 magnitudes corresponds to an absolute magnitude of -9.17, or roughly 360,000 times that of our sun. Its brightest stars are about of apparent magnitude 12.6 or absolute magnitude -2.8 or a luminosity of 1,000 times that of our Sun, and its horizontal branch giants are about of magnitude 15.6. Its overall spectral type has been determined as F3 or F4. The globular cluster is approaching us at 107 km/sec.
M15 is perhaps the densest of all (globular) star clusters in our Milky Way galaxy. It is still unclear if the central core of M15 is packed so dense simply because of the mutual gravitational interaction of the stars it is made of, or if it houses a dense, supermassive object, which would be resembling the supermassive objects in galactic nuclei. The one in M15 would among the nearest and better observable to us, being only little more remote than the Galactic Center and much less obscured by interstellar matter. Although the true nature of these objects remains obscure for the moment, many scientists believe they are strong candidates for "Black Holes".
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