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RA: 18h 23m 40.69s
Dec: −30° 21′ 38.8″
Ch: MSA:1414, U2:378, SA:22
Ref: SIMBAD, SEDS
Type: globular cluster
Mag: B=10.22, V=9.14
Synonyms: H I-050
Discovered in 1784 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "cL R vbM milky."
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, psvmbM, diam in RA = 5 seconds; all clearly resolved into stars barely discernible." On a second occassion he called it "globular, B, R, psmbM, diam 6 seconds in RA, barely resolved so as to be sure it consists of stars." His third observation was recorded as "globular, B, R, stars first g, then psvmbM, 3.5' or 4' diameter, clearly resolved into stars 16m, a fine object."
Described in the NGC as very bright, pretty large and round, well resolved and consisting of stars of 16th mag.
A study by W. W. Morgan of Yerkes Observatory indicates this globular cluster to have a spectral type of G2.
(Sulentic and Tifft 1973) notes that this is a 9.5 mag globular cluster.
by Jim Lucyk: Sky&Tel. 5/79 p447.
Vorontsov-Velyaminov, B. "Integral magnitudes of south star clusters", Astron. Nach. 228, 325. Comparing the brightness of the cluster with the extrafocal images of stars, he estimates the magnitudes as 9.0
"globular cluster, extremely condensed; not well resolved on the Bruce plates"
Bailey, S.I. (1908) A catalogue of bright stars and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.
RA 18 23 40.5 (2000) Dec -30 21 40 Integrated V magnitude 7.87 Central surface brightness, V magnitudes per square arcsecond 15.42 Integrated spectral type G4/5 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 2.50c: Core radius in arcmin .06. ["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) ]
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "8.5M; 3' diameter; unresolved glow with brighter center; 45' SE of 3M Delta SGR."
Coe, observing with a 13" f/5.6, notes: "Bright, pretty large, much compressed and round. It has a very bright middle and is resolved into 18 stars against a grainy backround at 165X. This a nice globular that doesn't get observed often."
30/04/93: Observing with a 6-inch f/8.6 Newtonian at 52x, the one-degree field is not too crowded. Two close-by 9th mag stars point to the cluster. Almost due west but slightly south of cluster is a small star, about 11th mag. The cluster is small and pretty bright.
1997 July 9, Wednesday, 20:00 - 22:00 Jonkershoek. 11x80's tripod-mounted. Moderate conditions. Quite like NGC 6652. In a group of 9th mag stars; it shows up as one of three in a row.
12-inch Meade, 40mm eyepiece, 53' fov. 1997-08-05, fair sky conditions "Very small starlike eliptical globular well distinguished in faint pin-point stars. Some mottled areas visible. The halo and core appear to be more or less the same size." [Magda Streicher, Pietersburg 23-53S, 29-28E]
12-inch f/10 SCT (EP: 2-inch 40mm SW 76x 53' fov; 2-inch 14mm UW 218x 23' fov)
Very small globular, faint stars in high power (218x) well distinguished. Some mottled areas can be seen between the scattering of faint stars. The halo and core appear to be more or less the same size, but the outer envelope is quite evident. Slightly brighter to the middle, which sometimes looks brighter than other times when sweeping is been done. Discovered in 1784 by William Herschel.
Location:Night Sky Caravan Park, Bonnievale.
Sky Conditions:Whole Milky Way is visible.The sky is clean.
Atmosphere stable with little interference.
In this globular cluster the stars are not resolved and no stars are seen in this cluster and that this globular cluster has the resemblance of a very small round snowball.This globular cluster has a slightly condensed nucleus.The nucleus of this cluster is slightly brighter compared to the stars on the far outskirts of this globular cluster.This globular cluster measures 2.7'*2.7'.Chart:No.326,NSOG Vol.2.
The Messier objects
The Bennett objects
The Caldwell list
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