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RA: 17h 04m 28.83s
Dec: −24° 45′ 53.3″
Ch: MSA:1395, U2:337, SA:22
Ref: SIMBAD, SEDS
Type: globular cluster
Mag: B=10.72, V=9.71
Synonyms: H VI-011
Discovered in 1785 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a fine miniature of the 19 nebula of [Messier] (which is a cluster of very compressed stars, much accumulated in the middle, 4 or 5' diameter, all the stars red), 2 or 2.5' diameter, the stars faint, red." In the Philosophical Transactions, 1818, William Herschel wrote: "1784. 20 feet telescope. A cluster of stars, which, in respect of the size of the whole as well as the distance and magnitude of the stars, is a good miniature of the 19th of the Connoissance observed a few minutes ago. The stars, like those of the foregoing cluster, preserve a faint red tint. It may be called the next step to an easily resolvable nebula. It is about 1.5' or 2' in diameter .. It is in the preceding branch of the milky way."
Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "globular, B, R, gbM, diam = 7 seconds, resolved into stars 16th mag."
description reads: "bright,large, round, compressed in the middle, well resolved into 16th magnitude stars."
"globular cluster, condensed"
Bailey, S.I. (1908) A catalogue of bright stars and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.
A study by W. W. Morgan of Yerkes Observatory indicates this globular cluster to have a spectral type of F8.
The RNGC (Sulentic and Tifft 1973) notes that this is a 10.5 mag globular cluster.
RA 17 04 28.8 (2000) Dec -24 45 53 Integrated V magnitude 8.83 Central surface brightness, V magnitudes per square arcsecond 16.65 Integrated spectral type F9 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 2.50c: Core radius in arcmin .07. ["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) ]
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "10M; 2' diameter; small, round with very dense center; unresolved; small triangle of 13.5 and 14M stars 2' E."
Hartung writes: "In a field profusely sown with small and faint stars is a round haze about 1' across, easy to see with a 4-inch telescope but needing an 8-inch to resolve it irregularly into gleaming points."
Houston writes: "Just 1.5 degrees north-northeast of M19 is NGC 6284. It is a bit small and fainter than [the nearby] NGC 6293, but still suitable for small telescopes. It is a nice cluster for beginners; searching for it provides good experience in hunting out challenging objects."
Steve Coe, using a 13" f/5.6, notes: "Pretty bright, pretty small, round, resolved at the edges at 135X."
Observer: John Callender
Instrument: 8-inch Dobsonian reflector Location: Carpinteria, CA, USA
Light pollution: light Transparency: fair Seeing: good
Time: Sat Jul 5 08:00:00 1997 UT Obs. no.: 200
Unable to spot it at 49x.
The cluster lies in a rich starfield of 9-10th magnitude stars, and just north of it is a nice but faint Southern Cross asterism. Just to the east of the cluster are three faint stars forming a very flat isoceles triangle. The globular is bright but quite small, and although not concentrated to a point, there aren't any obviously apparent outliers. Appears regularly round in form.
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.
Smaller, fainter, roundish soft light with no structure and not resolved stars. Just outside this globular to the east two stars visible.
8-inch f/10 SCT (EP: 1.25-inch 26mm SP 77x 41' fov; 1.25-inch 18mm SW 111x 36' fov) and 12-inch f/10 SCT (EP: 2-inch 32mm SW 95x 42' fov; 2-inch 14mm UW 218x 23arcmin; 2-inch 8.8mm UW 346x 15' fov)
Small and faint round puff of light in the dark of night with no structure and no resolved stars. Only with the utter most caution and high power a very few faint specks can be seen in the soft outer edge (218x and 346x). Towards the west in the field of view an 8th and 9th magnitude stars can be seen. Discovered in 1785 by William Herschel. (Mag 8.9; size 5.6'. )
Observing site: Pinnacles overlook
[17h 4m 30s, -24° 46' 0"] A small cluster, barely granulated with averted vision.
Sky Conditions:The fainter parts of the Milky Way are barely visible.Haziness only visible on the horizon.Atmosphere stable with little interference.
This globular cluster looks like a circular halo of light and that the stars in this cluster are not resolved at all.The nucleus of this cluster is strongly condensed towards each other.From the nucleus of this globular cluster the light of the stars grows brighter compared to the far outskirts of this cluster.Chart No.295,NSOG Vol.2.
The Messier objects
The Bennett objects
The Caldwell list
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