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RA: 17h 17m 59.27s
Dec: −23° 45′ 57.7″
Ch: MSA:1395, U2:337, SA:22
Ref: SIMBAD, SEDS
Type: globular cluster
Mag: B=11.49, V=10.33
Discovered by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "pF, R, gbM, r, 1'. No doubt it is a globular."
Probably small cluster. A poor plate.
The RNGC (Sulentic and Tifft 1973) notes that this is a 12.5 mag globular cluster.
The cluster glows at magnitude 10.7 and measures 4.3' across. Its concentration rating is 4.
RA 17 17 59.2 (2000) Dec -23 45 57 Integrated V magnitude 10.33 Central surface brightness, V magnitudes per square arcsecond 17.56 Integrated spectral type G0 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 2.50c: Core radius in arcmin .03. ["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) ]
Hartung writes that this globular is "of fairly compact type, a round haze about 1' across with no sign of resolution, faint but not difficult with an 8-inch telescope."
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "12M; 1' diameter; small and faint; unresolved; looks like EL GAL; 30' N of 5M Omicron OPH."
Steve Coe, using a 13" f/5.6, notes: " Faint, pretty large, somewhat brighter in the middle at 100X. There are few field stars near this globular because of nearby dark nebulae.
The first search for this cluster, using a two-inch refractor, failed to locate it. But the second search showed it as an elusive pretty faint object lying in a busy starfield of 10th magnitude stars. The cluster can be found easily less than a degree away from the very beautiful red, unequal double 39 Oph. Due north of 39 Oph is a slightly fainter star, and less than twice this distance further north lies the globular. The globular appears as a cottonwool tuft of light showing no detail. I was not expecting it to show as an extended nebulous patch, but rather as a star-like object. I thought one of the 9th magnitude field stars was the cluster, and only when I started examining these stars for an extended appearance did the cluster pop into view. Three of the field stars lying due north of the cluster form a right-angled triangle.
Observing site: Pinnacles overlook
[17h 18m 0s, -23° 46' 0"] This cluster looks like a faint, diffuse E0 galaxy. There was no granulation.
The Messier objects
The Bennett objects
The Caldwell list
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