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RA: 18h 27m 31.2s
Dec: +06° 34′ 12″
Ch: MSA:1271, U2:205, SA:15
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 32m
Mag: B=5.01, V=4.6
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Discovered by Caroline Herschel.
Synonyms: H VIII-072
Noted in 1788 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a cluster of coarsely scattered large stars. Caroline Herschel discovered it in 1783."
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 25' and the class as 1 2 pE.
The RNGC (Sulentic and Tifft 1973) notes that this is a 5.5 mag open cluster.
Doig, P. (1925) Notes on the nebulae and clusters in Webb's 'Celestial Objects for Common Telescopes' (Sixth edition, Vol.ii). Part IV. M.N.R.A.S., 36(2), 58.
Raab, S. (1922) A research on open clusters. Lund Medd. Astron. Obs. Ser. II, 28, 1.
Discussed, based of F-A plates.
Bailey, S.I. (1908) A catalogue of bright stars and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.
"A Catalogue of Estimated Parallaxes of 112 Nebulae, Open clusters and Star Groups", Vol 36 (4), p 107-115.
"irregaulr cluster of bright stars; contains long period variable T. Serpentarii." He gives the approx. diameter as 28 arcmin.
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Photo Index by Jim Lucyk: Burnhams V2 p1265, Deep Sky #23 Su88 p25.
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "5M; 20' diameter; bright, large and sparse; 65-plus 7M members; bright star just S and a bit E is 5.5M SAO 123516."
Steve Coe, using a 13" f/5.6, notes: "Bright, large, not compressed, pretty rich at 60X. This nice cluster is easy in the 11 X 80 finder, with many bright members, sevral are yellow or light orange in color. I counted 38 stars in this lovely cluster. 13" 60X--bright, large, stars 8..., little compressed, pretty rich, several nice chains of stars, 32* counted. Several stars show color, 2 blue and 3 yellow in cluster. A very rich field."
Observer: Todd Gross
Your skill: Intermediate - Many years
Date and UT of observation: 3/09/99 09:15 GMT
Location & latitude: 22 mi. West of Boston, Ma. 42.3N
Site classification: Suburban
Limiting magnitude (visual): approx. 4.7 zenith
Seeing (1 to 10 - worst-best): about 3
Moon up (phase?): Yes, last 1/4 (just over)
Weather: Crystal Clear
Instrument: C9.25" SCT f/10 f.l.2350
Magnifications: 123 & 87x
Filters used: none
Object data: Open cluster
Position: 18:28 +6:34
Personal "rating" (at this aperture, and sky condition): B/B-
Large, loose cluster, fairly bright stars, mostly of the same magnitude, randomly distributed. Pretty, but required even lower power for a better view.
Boston Meteorologist Todd Gross
Alldays (22.50S, 20.12E, 770m).
12-inch f/10 SCT (95x)
The first object was NGC 6633 in Ophuichus, with the constellation already descending in the West. My first impression revealed a bright grouping of stars of various magnitudes. The centre exhibited a few brighter stars in the shape of a semi-circle, along with a faint uneven string of stars to the east that drapes from North to South. Concluding the observation was a very tight group of six stars to the west.
1997 July 7, Monday, 21:00 - 24:00 Jonkershoek. 11x80's tripod-mounted. About 12 8th magnitude stars in an elongated (1:3) and narrowing rectangle. Bright star to the south-east. At the north-western edge of the cluster is a dark area; the rectangle of stars, plus other stars in the milk way field to the north-west, together make a much larger irregular scattered cluster, about 45' across, with a round, black hole in the centre! Quite remarkable!
The Messier objects
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