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RA: 17h 23m 34.99s
Dec: −17° 48′ 46.9″
Ch: MSA:1370, U2:338, SA:15
Ref: SIMBAD, SEDS
Type: globular cluster
Mag: B=10.01, V=8.9
Synonyms: H I-048
Discovered in 1784 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "B L R gbM easily resolvable." In the Philosophical Transactions, 1814, Herschel described it as "A miniature of the 9th of Connoissance des Temps [NGC 6333] (which is itself a miniature of the 53d [NGC 5024]. I suppose if I had looked long enough, I might have perceived some of the stars which compose it."
Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "globular, vB, R, vgvmbM, 90 arcseconds, resolved into stars barely discernble with left eye. A beautiful softly shaded object."
The NGC describes this globular cluster as "very bright, considerably large, very gradually very much brighter towards the middle, well resolved into 20th magnitude stars."
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
"globular cluster, extremely condensed."
Bailey, S.I. (1908) A catalogue of bright stars and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.
Bailey, examining a Bruce plate (Harvard Annals, Vol 72, No 2), describes it as "pretty faint, globular cluster, extremely compressed, faint stars, diameter 2.5'."
A study by W. W. Morgan of Yerkes Observatory indicates this globular cluster to have a spectral type of G5.
The RNGC (Sulentic and Tifft 1973) notes that this is a 9.5 mag globular cluster.
RA 17 23 35.0 (2000) Dec -17 48 47 Integrated V magnitude 8.25 Central surface brightness, V magnitudes per square arcsecond 17.09 Integrated spectral type G3 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 1.54 Core radius in arcmin .23. ["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) ]
Steve Coe, using a 13" f/5.6, notes: "Bright, pretty large, much brighter in the middle, three stars resolved across a very grainy cluster at 165X."
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "8.5M; 3.5' diameter; bright and small; individual stars not resolved at 200x."
Hartung writes "This is a wellcondensed type of globular cluster, a bright luminous haze with fading edges, about 3' across with no sign of resolution; the stars must be very faint and numerous. The bright centre 1.5' across is an easy object for a 3-inch telescope."
Bennett observed it with a 5inch short-focus refractor, including it in his list of cometary objects as number 93.
John Bortle (Webb Society Quarterly Journal, January 1976) using 10x50 binoculars, estimates the visual magnitude as 8.4.
Location: Campsite (South 23 16 East 29 26).
Sky conditions: Very clear semi transparent.
Instrument: Meade 8" (Super plossl 26mm and wide-angle 18mm eyepiece).
Date: 26 to 28 April 1998.
Field of view: 36.2arc minutes.
Globular close to M9, but smaller and brighter. Hazy edges forms an envelope, then slowly getting brighter to a sudden bright core. No stars resolved but standing out towards a busy starfield. Line of stars running from east to west forming an asterim outside this globular to the north.
12-inch f/10 SCT (EP: 2-inch 40mm SW 76x 53' fov; 2-inch 32mm SW 95x 42' fov; 2-inch 14mm UW 218x 23' fov)
Smaller yet brighter than Bennett 92 (NGC 6333 or M9). Soft outer edges, slowly brightens up to the centre and stands out well against the background. The smaller outer section of the globular is just a soft envelope (218x). Cannot resolve the stars yet stand out against a busy star field. The exceptionally busy star field with stars on the south side appears as water droplets dripping out of this globular cluster. (Mag 8.2; size 7.2'; brightest star 15.1 mag. )
A 15.5-inch reflector shows this cometary globular situated in a rich starfield sprinkled with large and small stars. The cluster is pretty bright and its stars are evenly distributed, not forming a nucleus. There does, however, appear to be a fainter outer envelope. No detail is visible across the globular's disk. A quarter of a degree south lies an 8th magnitude star. The globular appears to be a smaller version of M 9.
1995-06-01: 11x80. Kelsey Farm. 23:00 SAST. This cluster is a neat little object, and needs careful attention, because while it is quite bright - I estimate it probably brighter than 9th mag - it isn't very large in binoculars, so it looks like a slightly out of focus field star - there are a number of similar mag stars in the vicinity. It sonly when you pay attention that you notice that the star has a real nebulous envelope.
1997 July 7, Monday, 21:00 - 24:00 Jonkershoek. 11x80's tripod-mounted. Easy as a roughly 9th magnitude star, of which there are many in the field. Stellar at a quick glance, but attentiopn shows the distinguishing fuzzy halo. Quite a contrast to M9 nearby.
Location:Night Sky Caravan Park,Bonnievale.
Sky Conditions:Whole Milky Way is visible.The sky is clean.
Atmosphere stable with little interference.
This globular cluster is seen as a round snowball of light. I have found no resolution of stars in this cluster cluster and that all the stars are unresolved which makes this cluster look like a halo in space.The stars in this globular cluster makes this cluster look very strongly condensed.The nucleus of this cluster is brighter compared to the stars on the outskirts of this cluster.This globular cluster measures 11.2'*11.2'Chart No:299,NSOG Vol.2.
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:Medium Surface Brightness.
Challenge Rating:Fairly easy to observe in dark skies in a medium aperture telescope.
Overall Shape:Oval appearance as a fluffy snowball of bright stars.
Are individual stars seen? No,this cluster has a granular appearance.
How are the stars concentrated towards the nucleus? It is a compact cluster and well arranged into bright stars spherically concentrated towards the center.
Estimate the size of the nucleus vs.halo:Nucleus(4.9') Halo(7.2').
Are there clumps/chains of stars? Yes,there are a few faint stars of 7th to 8th magnitude concentrated towards the center.
Prominent empty spaces/starless patches? Yes,there are a few starless patches.
Observing site: Pinnacles overlook
[17h 23m 36s, -17° 49' 0"] A small, bright cluster. It looked granulated, despite the HRNGC's assertion that the stars were 20th Mv and below.
The Messier objects
The Bennett objects
The Caldwell list
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