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RA: 16h 57m 8.99s
Dec: −04° 05′ 57.6″
Ch: MSA:1324, U2:247, SA:15
Ref: SIMBAD, SEDS
Type: globular cluster
Mag: B=?, V=6.4
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This globular cluster in Ophiuchus lies just over 3 degrees away from the globular NGC 6218, Messier 12, and together they make a nice pair in a binocular field.
In the Philosophical Transactions, 1818, William Herschel wrote: "1783, 7 feet telescope. With 227 power I suspected it to consist of stars; with 460 I can see several of them, but they are too small to be counted. 1784, 1791, 20 feet telescope. A beautiful cluster of extremely compressed stars; it resembles the 53d; and the most compressed part is about 3 or 4' in diameter."
Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "globular, fine, L, R, B, gmbM, diam 5', with straggler, several of which are of larger sizes, to about 12' diam; all resolved into stars 11..15th mag, very compressed."
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
RA 16 57 08.9 (2000) Dec -04 05 58 Integrated V magnitude 6.60 Central surface brightness, V magnitudes per square arcsecond 17.69 Integrated spectral type F3 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 1.40 Core radius in arcmin .86. ["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) ]
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.
The RNGC (Sulentic and Tifft 1973) notes that this is a 7.5 mag globular cluster.
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 6.85.
"! globualr cluster, fairly condensed"
Bailey, S.I. (1908) A catalogue of bright stars and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.
Some observers have commented on the pear-shape appearance of this cluster. A 10-inch or larger will reveal the individual cluster members. Look out for the well populated, rich surrounding star-field.
Notes that this cluster has a bright milky centre and considerably fainter edges, which a 12-inch will resolve into stars.
Harrington, P. (1986) An observer's guide to globular clusters. Sky&Telescope, Aug, 198.
.. my 8inch refecltor reveals stars around the edge of M10, but the nucleus remains an indefinite blaze.
Bortle (Webb Society Quarterly Journal, January 1976) using 10x50 binoculars, estimates the visual magnitude as 6.9.
:"This fine globular is rather well resolved even at low powers. It is about 12' in diameter, and has a rather ragged circular shape with stars resolved across its face. A chain of 6 foreground stars starts north of the globular and ends to its south, seemingly bisecting the cluster."
(e-mail: firstname.lastname@example.org, web: http://users.aol.com/JTomney); Instrument: 6-inch equatorial reflector Location: Marriotsville (Alpha Ridge), MD, USA; Light pollution: light Transparency: good Seeing: good; Time: Wed Jun 4 15:15:00 1997 UT Obs. no.: 156
Amid the semi-dark skies at Alpha Ridge I was surprised at how readily I could scoop up M10 and its neighbor M12 in the 7x50 binoculars. I'd guesstimate the magnitude to be somewhere around 8-8.5 for these two. The star hop was a little tedious but not bad, and panning with the 42mm Ultima soon brought M10 into view. It was steady if not powerful, strong enough to take direct vision yet improved by averted vision. The field at 28x was pleasant but had nothing significant. At 75x the view was best, bringing forth a little speckling of resolution on the fringes when averted vision was used. The globular has a rather even distribution of light with gradual and subtle brightening towards the core. The visible size would be somewhere in the neighborhood of 5 arc-minutes. Bumping the magnification up to 124x did little to improve the view although it may have been possible with study to tease a bit more detail from the globular; in general 124x seemed to be too much magnification for M10 as it became dimmer.
Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "7M; 8' diameter; wonderfully studded with 10-11M stars over diffuse glow of unresolved main body; brighter stars concentrated over E sector; one of the prettier sights aloft! M-12 is 3.1 degrees to NW; great binocular pair!."
(e-mail: email@example.com, web: http://www.west.net/~jbc/)
Instrument: 8-inch Dobsonian reflector Location: Carpinteria, CA, USA
Light pollution: light Transparency: good Seeing: excellent
Time: Sat Jul 12 08:00:00 1997 UT Obs. no.: 210
Easily swept up at 49x. A big, bright globular, the brigher stars resolved at 49x, with a fairly bright central glow behind them.
Steve Coe, using a 13" f/5.6, notes: "Bright, large, compressed, elongated 1.5X1 in PA 45, at 220X. It is unmistakeable in binoculars, with M 12 nearby. Again there are many streamers of stars. The most prominent is to the NE. There are several orange stars involved, one of 12th mag on the eastern side. In 1851 Lord Rosse, using the 72" speculum, reported a dark lane going through this cluster. The next time I get an evening on a 72" I will confirm the observation. The inhabitants of these two clusters would see each other as a 2nd magnitude object! Sentinel 13"--obvious in 11X80, 150X--Bright, large, round, very much brighter middle, well-resolved. 220X--110* counted, several nice chains, two on opposite (N-S) sides curve opposite directions, like a garden sprinkler. There is an 11th mag orange star on N side. Averted vision "fills in" the cluster with many stars. 330X--dark marking on E side, dark oval about 2 arcmin from core center, at the edge of the compressed middle section."
In a 15.5-inch reflector, it is a very striking globular, with no clear distinction between nucleus and out-lying region, being all nucleus. The stars in the nucleus are quite well resolved, more so that in M12. One gets the impression is that M10 is slightly larger than M12, but this may be because the nucleus is more prominent. There are no noteworthy star-chains or particularly bright field stars. However, looking for structure plays havoc with your eyes. Seems there is a dark patch to the south and on the outside of the globular (absence of fainter stars, although there is a star right in the centre of this void), and the globular seems at times to have a core extended towards the east in a rough rectangle. Note that these shapes were best seen with averted vision whilst resolving stars in the nucleus. Peet also noted the northern elongation, as well as the lightless patch and its star. A more subtle feature seems to be a dark arc on the S side of the nucleus, running west-east. I feel that these changes of appearance are caused by averted vision allowing different parts of the mottled globular to come to ones attention. The more contrasty view of the 17mm eyepiece makes the elongation almost Due north, (i.e. north of the rectangle) more apparent. To recap, we have 2 elongations: there is a broad shaft of stars going northnorth-east from the nucleus, and a rectangular elongation north-east. Also look out for an interesting feature of the NNE extension: it is mainly marked down its centre by a line of 3 brighter equally-spaced stars. These stars dominate this appendage; the other stars in this extension are cF; nebulous. One can follow this even, widely-spaced, chain right across the centre of the globular, with 3 stars in the nucleus, and the 7th and last star in the centre of the dark gap to the south ( mentioned earlier). Once your attention has been drawn to it, these 7 stars are very obvious. In the 17mm, the NE rectangular extension appears less striking than this chain. The extension consists of about 4 stars in each of the longest sides of the rectangle (i.e. running NE), and very few faint stars are visible in this high-contrasty field. Fits 3 times into 17mm field. Intensely interesting object because of the many patterns your mind and eye trace.
1995-06-01: 11x80. Kelsey Farm. 22:00 SAST. A bright globular in a busy field, large and small stars. Cluster appears mostly nucleus with only a small fringe. Very similar to NGC 6218 (M12) nearby. Brighter, and mayb a bit smaller.
1997 July 8, Tuesday, 20:55 - 23:30 Jonkershoek. 11x80's tripod-mounted. Smaller and brighter than M12. Moderate centre, noticeable fringe. Brighter in the middle than M12. Flanked by two triangles of stars.
12-inch f/10 SCT (EP: 2-inch 40mm SW 76x 53' fov; 2-inch 32mm SW 95x 42' fov; 2-inch 14mm UW 218x 23' fov)
Lovely and outstanding globular also know as M10. The inner core is relatively large and oval, very tight and bright in contrast to the outer flimsy edge. Very characteristic in shape with stars in lanes and shapes, even a few dark areas in between (218x). Towards the outer tenuous edge a few dainty strings can be seen which seems to becoming busier towards the south. In the eastern section open spaces made themselves evident. Outstanding object that displays a handful of yellow stars dotted in between the glittering stardust. (Mag 6.6; size 15.1'; brightest stars 12.0 mag)
2007 April 14, 01:10 UT
8-inch f5 Dobsonian (EP: 15mm 45' fov)
Conditions: Very slight haze but Milky Way clearly visible
Globular cluster (M10) in Ophiuchus. Reasonably easy to locate. Unlike other globular clusters that I've seen i.e with averted vision the brighter nucleus seems to be off centre towards north-west. The less denser fan shaped halo radiating to north-east. I cannot resolve any stars. There are four bright stars in the form of a cross in the same field with the long axis north-south.
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 is very well resolved into 6th to 8th magnitude stars and that the stars in this cluster is slightly more concentrated towards each other like a diffuse sharp snowball.Towards the central core of this cluster the stars are spherically concentrated towards each other as a white halo of soft greyish light.This globular cluster measures 9.2'x 7.6'.Chart No:292,NSOG Vol.2.
Instrument:12"Dobsonian Reflector Telescope.
Sky Conditions:The fainter parts of the Milky Way are barely visible.
Transparency of the Sky:Haziness only visible on the horizon.
Seeing:Atmosphere stable with little interference.
First Impression:Globular Cluster.
Chart Number:No.12(Extract taken out of "Atlas of the Night Sky").
Brightness Profile:High Surface Brightness.
Challenge Rating:Spectacular under dark skies in a 10-12"inch telescope.
Overall Shape:Oval and well defined.This globular cluster presents bright individual stars being clearly resolved in the center of this cluster.There are also bright stars clearly resolved on the outskirts of this cluster.
Are individual stars seen? Yes,this globular cluster is well resolved into thousands of bright individual stars.
How are the stars concentrated towards the nucleus? The stars in this globular cluster is strongly concentrated towards each other in an almost spherical halo.
Estimate the size of the nucleus vs.halo: Nucleus(15.1') Halo(13.9').
Are there clumps/chains of stars? Yes,bright individual stars are seen in the whole cluster.
Prominent empty spaces/starless patches? Yes,some starless patches are noticeable on the outskirts of this cluster.
Observing site: Pinnacles overlook
[16h 57m 6s, -4° 6' 0"] A large, loose globular. It's quite bright. A few 12-13 mv stars, the rest a granulated mass of fainter stars. (Brightness from Hurley et al, Astronomical Journal, vol. 98, Dec. 1989, p. 2124-2145)
The Messier objects
The Bennett objects
The Caldwell list
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