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RA: 17h 21m 10.14s
Dec: −19° 35′ 14.7″
Ch: MSA:1370, U2:338, SA:22
Ref: SIMBAD, SEDS
Type: globular cluster
Mag: B=11.25, V=10.99
Synonyms: H I-149
Discovered in 1786 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "cB, pS, lE, easily resolvable."
The NGC description reads: "considerably bright, pretty small, slightly elongated, extremely mottled."
2'x2' cluster, very condensed at the centre, with a small vacant space in n.f. portion, possibly due to absorption.
RA 17 21 10.2 (2000) Dec -19 35 14 Integrated V magnitude 9.66 Central surface brightness, V magnitudes per square arcsecond 17.44 Integrated spectral type G3/4 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 2.50c: Core radius in arcmin .05. ["Catalog Of Parameters For Milky Way Globular Clusters", compiled by William E. Harris, McMaster University. (Revised: May 15, 1997; from http://www.physics.mcmaster.ca/Globular.html; Harris, W.E. 1996, AJ, 112, 1487) ]
The RNGC (Sulentic and Tifft 1973) notes that this is a 11.5 mag globular cluster.
Hartung writes that the cluster is "rather faint and irresolvable; it is fairly compressed, irregularly round, about 40" across...A field star is near S.p. A 6-inch telescope shows the object quite plainly."
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "11M; 1' diameter; small and distant; individual stars not resolved; 15' to NNW is DBL ST ADS 10465 (1.9" separation @ PA 140; 6.3-7.4M)."
Michael Sweetman (Tucson, Arizona, USA) observing with a 6-inch refractor, writes in the The Webb Society Nebulae and Clusters Section Report No. 10, July 1992: "At x48, small and faint but noticeable and showing slight increase in brightness towards the centre. Bright star lies just outside the envelope on the N side. x204: appears circular, the envelope shows no edge and the bright core is circular in shape. No details noted."
Steve Coe, using a 13" f/5.6, notes: " Pretty bright, small, round, bright nucleus, two stars are resolved at 165X. There is an 11th mag star on the SW side."
In a 15.5-inch telescope at 220x, the cluster is shown to lie in a busy starfield populated with small and faint stars scattered about the whole field of view. The cluster, although quite faint and small, does seem as if it is pretty much concentrated since it appears as if there is a faint outlying halo. Just south of the cluster, about a cluster diamater distant, lies a 10-11th magnitude star. The globular lies in the same two-degree field as the globulars NGC 6333 to the northwest and NGC 6356 to the north.
Instrument:12"Dobsonian Reflector Telescope.
Sky Conditions:The fainter parts of the Milky Way are barely visible.
Transparency of the Sky:Haziness only visible on the horizon.
Seeing:Atmosphere stable with little interference.
First Impression:Globular Cluster.
Chart Number:No.117(Extract taken out of "Star Gazer's Deep Space Atlas").
Brightness Profile:Low Surface Brightness.
Challenge Rating:Easy to observe in a 12"inch telescope under dark skies.
Overall Shape:Oval,it appears as a mottled faint snowball.
Are individual stars seen? No,this cluster is unresolved.
How are the stars concentrated towards the nucleus? It is well compacted towards the center of this cluster.
Estimate the size of the nucleus vs.halo: Nucleus(1.2') Halo(3.0').
Are there clumps?Chains of stars? no.
Prominent empty spaces/starless patches? There are no starless patches.
Observing site: Pinnacles overlook
[17h 21m 12s, -19° 35' 0"] A rather small GC, the stars are faint, I only glimpsed ~4 of them. The center was fairly bright.
The Messier objects
The Bennett objects
The Caldwell list
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