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RA: 17h 04m 42s
Dec: −37° 59′ 0″
Ch: MSA:1440, U2:376, SA:22
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 22p
Mag: B=5.78, V=5.4
James Dunlop discovered this object from Paramatta, New South Wales, and included it as No. 556 in his catalogue of 1827. Using a 9-inch f/12 telescope, he described it as "a curiously curved line of pretty bright small stars, with many very small stars mixt."
Discovered by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "a p rich, L, pB, cluster VII class, of loose stars 9, 10, 11th mag, which fills 2/3 of field."
The NGC description reads: "Open cluster, large, pretty rich, only slightly compressed, stars of magnitude 9..11."
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 9' and the class as 2 2 p.
The RNGC (Sulentic and Tifft 1973) notes that this is a 8.5 mag open cluster.
Photo Index by Jim Lucyk: Burnhams V3 p1681.
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 star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Harrington calls this an "easy open cluster to glimpse with just about any optical aid. Binoculars reveal a tight swarm of 7-9th mag stars..." He likens it to "a crooked cross" and notes that Luginbuhl and Skiff describes it as "20 stars arranged over haze like Christamas tree lights." Harrington notes "as aperture and magnification increase, the cluster's structure appears to change as many fainter stars flood the field. An 8-inch telescope resolves about two dozen, while a 12-inch adds an additional dozen or so within the cluster's 8' diameter."
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "5.4M; 9' diameter; rich, large and compressed; 25-plus 9 thru 11M members; 2.5 degrees E of DBL ST Mu SCO; good binocular object."
Steve Coe, observing with a 17.5" f/4.5 at 100X, notes: "Pretty bright, pretty large, 30 stars in a nice Milky Way field at 100X. Several of the brighter members can be seen in the finderscope.
Date and Time: 31 October 2008, 20:30
Location: Prince Albert (Western Cape, South Africa).
Instrument: Orion XT10 10" f/4.7 Dobsonian Reflector
Eyepieces: 10mm (120x, 26′ FOV), 25mm (48x, 1° FOV)
Sky Conditions: Clear. Seeing: 5/10. Transparency: Average
Windy, waxing crescent moon
48x: Small open cluster about 10′ in size. A definite arrow shape can be seen pointing in a slightly NW direction. One bright star is visible towards the west and 2 towards the NW. 34 stars counted using both direct and averted vision. Stars vary considerably in brightness, with fainter stars forming the arrow shape.
At 120x: The stars in the arrow shape is more visible and it is easier to make out the fainter stars in the surrounding area.
Location: Night Sky Caravan Park, Bonnievale.
Date: 2016 Oct 30, Sunday.
Time: 21:10 SAST
Telescope: Little Martin (4-inch f/6.5 Celestron refractor)
19mm Panoptic (35x): Wow, gorgeous shape! A bright cluster with striking lines. Most obvious is a broad V (spanning the entire cluster) flying north-west, or perhaps it's a lobsided rectangle.
This interesting open cluster looks like an elongated triangle with the apex separated from the main body. A 2-inch refractor shows one prominent member which appears double, and four or so smaller stars, the other members forming a mottled background.
1997 March 15. Jonkershoek. 11x80 tripod mounted. No moon. Noticeable rectangular knot of large and small stars.
The Messier objects
The Bennett objects
The Caldwell list
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