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RA: 17h 17m 7.27s
Dec: +43° 08′ 11.5″
Ch: MSA:1135, U2:81, SA:8
Ref: SIMBAD, SEDS
Type: globular cluster
Mag: B=?, V=6.3
This globular cluster lies midway between the Keystone of Hercules and the head of Draco. It was discovered by J Bode in 1777, and described in the NGC as very bright, very large, extremely compressed in the middle, stars resolved throughout, consisting of faint stars only.
In the Philosophical Transactions, 1818, William Herschel wrote: "1799, 7 feet finder. It may just be distinguished; it is but very little larger than a star. 1783, 2 feet sweeper With 15 power it appears like a clouded star. 1783, 7 feet telescope. With 227 power resolved into very small stars; with 460 power I can count many of them. 1799, 10 feet telescope. With 240 power the stars are much condensed in the centre. 1783, 1787, 1799, 20 feet telescope. A brilliant cluster, about 6 or 7' diameter. 1805, large 10 feet telescope. The most condensed part is3' 16 seconds diameter."
In the 5th edition of Webb's Celestial Objects for Common Telescopes it is described as "very fine cluster, though not equal to M13; less resolvable; intensely bright in centre. D'Arrest justly calls it, with his 11-inch achromat at Copenhagen, 'acervus adspectu jucundissimus.' In Hershel's reflectors, 7' or 8' diameter. Buffham, with 9-inch speculum, found stars bright and more compressed than in M13, but blaze resolved by glimpses. Spectrum as M13. E. of Rosse, possible spiral, nucleus barely, if at all, resolved."
Doig, P. (1925) Notes on the nebulae and clusters in Webb's 'Celestial Objects for Common Telescopes' (Sixth edition, Vol.ii). Part II. M.N.R.A.S., 35(8), 280.
Vorontsov-Velyaminov, B. (1925) "Catalogue of integrated magnitudes of star clusters", Astron. Nach. 226.195. Comparing the brightness of the cluster with the extrafocal images of stars, he estimates the magnitude as 6.72.
RA 17 17 07.3 (2000) Dec +43 08 11 Integrated V magnitude 6.44 Central surface brightness, V magnitudes per square arcsecond 15.58 Integrated spectral type F2- Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 1.81 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) ]
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
"globular cluster, fairly condensed."
Bailey, S.I. (1908) A catalogue of bright stars and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "6.5M; 8' diameter; rival of M-13! well resolved and grainy; compact, dense core; brighter stars are 12M; resolved balance are 13M or dimmer; M-13 is larger, has less center condensation, is less coarse; both are brain-burners!."
Hartung notes: "In clear weather it is well resolved, the centre broad and very bright with irregularly scattered outliers about 5' across, which even 10.5cm will show quite plainly."
Harrington, P. (1986) An observer's guide to globular clusters. Sky&Telescope, Aug, 198.
This is one of the unsung glories of the heavers. It is said this cluster is often overlooked because observers favor nearby M13. What a shame! Binoculars show a fuzzy patch while a 6 inch will resolve its edges. Larger apertures unravel its splendor and may reveal the dark patches that Lord Rosse saw…
As seen with an 8-inch it appears about 8' in size, whilst a 12-inch will show it extending to 10' The late John Mallas, using a 4-inch refractor at 214x was able to see individual stars within the globular.
The mean blue magnitude of the 25 brightest stars, excluding the 5 brightest, is 13.96.
John Bortle (Webb Society Quarterly Journal, January 1976) using 10x50 binoculars, estimates the visual magnitude as 6.3.
Observer: John Callender
Instrument: 8-inch Dobsonian reflector Location: Carpinteria, CA, USA
Light pollution: light Transparency: good Seeing: fair
Time: Sun Jun 29 09:30:00 1997 UT Obs. no.: 168
A beautiful globular at 49x. Larger than NGC6229 (which I had just looked at), the outer reaches were clearly resolved into mottled stars. At 122x even the center began to show a mottled appearance, with some darker patches here and there. At 244x the center section appeared irregular. I think 122x gave the most aesthetically pleasing view.
The RNGC (Sulentic and Tifft 1973) notes that this is a 7.5 mag globular cluster.
POSS: m9 * (SAO 46617) 6'.2 E/sl N.
Sandage & Walker: * 3'.0 SW V ~12.0; pair NE: V=12.03,13.29; 9".9; pa5.
7x35mm - much smlr & more sharply concen than M13. *ar center. BS, 29Apr1992,
7cm - intensely br cl @ 30x, where it appears grainy. 50x/75x: halo reaches
beyond m12.5 * on SW, or 1/2 way to br * E. mod sharp concen to intense
br cen. about a doz br *s plus huge number additional at threshold.
excellent object! BS, 15Apr1993, Anderson Mesa.
15cm - found by going N from e Her. vbr and evenly concen from dim outliers to
intense core. at 203x it is well res and about 8' diam. FtL.
- partially res @ 50x, somewhat fntr, but more strongly concen than M13.
140x/165x: outliers to 9' radius, well beyond m9.5 * E. inner halo
reaches 1/3 way to this *, or about as far as or sl beyond m12.5 * SW.
from this radius brtness rises exponentially---vflat at first, then
suddenly mod-sharp concen twd the center. BS, 8May1989, Anderson Mesa.
- isolated pair m12,13 5' NNE in outer halo. inner halo light flattened on
SE side, delimited on inner extreme near core boundary by string of m13
*s in line going NE-SW. 295x shows core pretty clumpy, not well res.
BS, 29Jun1989, Anderson Mesa.
25cm - br and well res @ 179x. star chains extending out in spiral patterns.
about 200 *s res w/underlying haze.
- outliers elong NE-SW. 5'x3'.5 overall; core 2'.5 diam.
- br, more concen than M13, smlr. well res. distinctly elong pa20-25.
overall size 9'x6'; flattening sharpest on SE side. only outliers elong,
core circ 2'.5 across. brtst part 1'.25 acorss loses res. m10 * 6' E,
m11 * 3' SW. 23May1982, Anderson Mesa.
30cm - smlr than M13, 8' diam total, core 4'. bright, concentrated. N side of
core is dk and pointed. well-res.
24/05/93 01:54 Very pleased as I have been able to pick up this globular in the 11x80's. This northern (+43°) cluster does not rise very high above the horizon from Stellenbosch, and I viewed it in the glare of Stellenbosch's lights -- in fact it lay nine degrees above a nearby street-light! Even so, it was easily visible as a pretty bright nebulous star to the southwest of Iota Her.
Globular Cluster, Hercules
Location: Campsite (23 16 South - 29 26 East).
Telescope: Meade 8" 18mm eyepiece, 36 arcmin f.o.v.
Date: August 1998.
Sky conditions: Not very good.
Description: Half the size of M13, this globular also beautiful with a core initially lightening slowly then suddenly growing brighter to a compressed middle. Scanty outliers with a companion star to the east edge rounds it off beautiful.
Alldays (22.50S, 20.12E, 770m).
12-inch f/10 SCT (218x, 346x)
Half the size of M 13, this globular also beautiful with a core initially lightening slowly then suddenly growing brighter to a compressed middle. Scanty outliers with a companion star to the east edge rounds it off beautiful. The galaxy is on IC 4645 is on its western edge. Hand full of stars accompany a strong middle lovely haze of faint stars around it. Visible only 25 brighter stars about 13magnitude. Very dense core southwet of Iota Hercules. The outliers is prominent.
Observing site: Little Tycho Observatory
[17h 17m 6s, 43° 8m 0s] Partially resolved at 80x. A color-magnitude graph found online shows that most of the stars are fainter than 14 Mv. Weird. I saw at least 30 of them, and granulation indicating many more. I suspect that Burnham, who mentions that the stars are 12th and below is correct. A most magnificient assemblage of stars.
The Messier objects
The Bennett objects
The Caldwell list
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