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NGC 6539 (14,903 of 18,816)

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NGC 6539

NGC 6539, C 1802-075, GCl 85, GC 4370

RA: 18h 04m 49.74s
Dec: −07° 35′ 9.1″

Con: Ophiuchus
Ch: MSA:1320, U2:294, SA:15

Ref: SIMBAD, SEDS

(reference key)

Type: globular cluster

Mag: B=?, V=9.33

Size: 7.9′
PA: ?

Remarks

Discovered by the Danish astronomer Theodor Brorsen in 1856.

Published comments

Sulentic & Tifft (1973)

The RNGC (Sulentic and Tifft 1973) notes that this is a 12.5 mag globular cluster.

Harris, W.E. (1997)

RA 18 04 49.8 (2000) Dec -07 35 09 Integrated V magnitude 9.33 Central surface brightness, V magnitudes per square arcsecond 19.31 Integrated spectral type G4: Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 1.60 Core radius in arcmin .54. ["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) ]

Shapley, H. (1930) "Star Clusters" Harvard Obs. Monographs No. 2

Included in a list of doubtful objects;. A very faint cluster in a large obscured area.

Helwan Obs. Bulletin No 21 (1920)

vF, 5'x5', globular cluster.

Melotte, P.J. (1915)

A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.

Modern observations

Tom Lorenzin

Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "12M; 2.5' diameter; small, round, faint and unresolved; 14M star 2' NW of core; DIFFICULT! 50' to SW is DBL ST Tau OPH."

Walter Scott Houston

Houston calls it a difficult object, 2' across and of 12th magnitude.

Hartung, E.J. (1968) Astron.Obj.South.Tel

Hartung describes this globular as a faint round haze nearly 3' wide, rising a little and broadly to the centre with no resolution apparent with a 12-inch, although a few faint nearby stars near may be outliers.

Steve Coe

Steve Coe, using a 13" f/5.6, notes: " Faint, pretty large, round, little brighter in the middle at 165X. This globular is in a very dark, star poor field."

Steve Coe, observing with a 13" f/5.6, notes: "Faint, pretty large, round, not brighter in the middle at 135X. This globular is somewhat mushy, and no resolution can be seen at powers up to 250X."

Observer: Steve Coe

Your skills: Advanced (many years)

Date/time of observation: 25 July 98

Location of site: Strawberry, Arizona USA (Lat +34, Elev 7000 ft)

Site classification: Rural

Sky darkness: 8 1-10 Scale (10 best)

Seeing: 7 1-10 Seeing Scale (10 best)

Moon presence: None - moon not in sky

Instrument: 13" f/5.6 Newtonian on Bigfoot German EQ

Magnification: 100X

Filter(s): none

Object(s): NGC 6539

Category: Globular cluster.

Constellation: Oph

Description:

100X--faint, pretty large, brighter middle, irregularly round, resolved even at 100X, about 8 very faint stars seen, better resolved with averted vision. There is an 11th mag star at the edge of this globular, it is in a PA of 330 degrees. This low surface brightness cluster is not helped with higher powers.

Contemporary observations

Auke Slotegraaf

1995 May 30

11x80.Technopark. 23:00 SAST. Hazy sky. Not found.

1995 June 01

11x80. Kelsey Farm. 23:00 SAST. Not visible, neither is the IC globular nearby.

1997 July 07

1997 July 7, Monday, 21:00 - 24:00 Jonkershoek. 11x80's tripod-mounted. Most extremely faint globular cluster to date. At first, not seen. Then, seen. At a third look, not seen! Certainty: 40% seen. Stars of 9.5 well seen.

Tom Bryant

2010 5 20 2:46:52

Observing site: Little Tycho Observatory

Telescope: C-8

[18h 4m 48s, -7 35' 0"] Field found, not found.

2010 7 3 23:6:33

Observing site: Pinnacles overlook

Telescope: C-11

[18h 4m 48s, -7 35' 0"] An obvious, faint smudge. No resolution.

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