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RA: 17h 50m 42s
Dec: −30° 13′ 0″
Ch: MSA:1415, U2:377, SA:22
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 12rn
Mag: B=?, V=8.2
Synonyms: H VI-013
Discovered in 1785 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a cluster of small and pretty compressed stars of several magnitudes, 5' or 6' diameter, not very rich."
Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "pretty rich, irregularly round, stars 13m, a cluster with a great black cut acorss it; 6' diameter, with many outliers." On a second occassion he called it "a remarkable cluster, divided into two by a broad vacant straight band, irregularly round, 8' diameter, stars 12..15m, See fig 6, Plate V." He also mentions this cluster in his comment on NGC 5128: "On the other hand we have, in the completely resolved cluster,[NGC 6451], an object which, removed to such a distance as to appear nebulous, would present a considerably approach to it in point of general aspect."
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 6' and the class as 2 2 m.
Raab, S. (1922) A research on open clusters. Lund Medd. Astron. Obs. Ser. II, 28, 1.
Discussed, based of F-A plates.
(Sulentic and Tifft 1973) notes that this is a 8.5 mag open cluster.
Photo Index by Jim Lucyk: Sky&Tel. 7/69 p58 (drawing by J. Herschel).
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Houston, W.S. (1969) Deep-sky Wonders: NGC 6451. Sky&Telescope, July, 58.
discusses this object and its surroundings; Gerald B. Fifer's "keyhole" in Scorpius; sketch by Fifer and h.
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "9M; 6' diameter; fairly large, rich and compressed; 50-plus 10 thru 13M members."
Steve Coe, observing with a 17.5" f/4.5 at 100X, notes: "Bright, pretty large, pretty rich, compressed open cluster at 165X. It is bright enough that it can be seen in the 8X50 finder. It includes a close triple star which appears nebulous at low powers and is resolved at 320X. I estimated 50 members in the cluster and it includes a dark lane almost down the middle of the cluster.
Observing with a 6-inch f/8.6 Newtonian at 52x, the cluster shows half a dozen or so 9..10m stars forming a dim, irregular grouping. There is either much unresolved haze inbetween the stars, or the optics are dewed.
Alldays (22.50S, 20.12E, 770m).
12-inch f/10 SCT (95x, 218x)
Faint slightly round haze and care many faint stars involved. The cluster is sharp define towards the NW spraying out towards SE. A relatively long string can be seen hanging on the cluster on the west of the field of view. It looks like a double star towards the middle section.
The Messier objects
The Bennett objects
The Caldwell list
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