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RA: 16h 57m 58s
Dec: −45° 56′ 36″
Ch: MSA:1480, U2:407, SA:22
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 23r
Mag: B=6.14, V=5.9
Discovered by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "Cluster class VIII; loose and straggling; place that of a double star in central more condensed group; has a 8th mag star S.f. 5' and another 7th mag more remote."
The NGC calls it "An open cluster, large, only slightly compressed, stars of magnitude 8..12."
Bailey, examining a Bruce plate (Harvard Annals, Vol 72, No 2), describes it as "Milky Way, coarse cluster of half a dozen bright stars, and many faint stars, diameter 15'."
"Cat. of Open Cl. south of -45° Decl.", Mem. 17 Mnt Stromlo Obs.
Moffat, AFJ & Vogt. N. (1975) "Southern Open Star Clusters VI. UBV-H-beta Photometry of 18 Clusters from Centaurus to Sagittarius." Astron.Astrophys.Suppl., 20, 155-182. [image, table]
d = 0.95 kpc.
The RNGC (Sulentic and Tifft 1973) notes that this is a 8.0 mag open cluster.
Phil Harrington (1990, Touring the Universe through Binoculars) calls it a "poor harvest of about 15 stars, with the brightest being about 8th mag. Large binoculars should be used to positively identify this weak 8' diameter open cluster. A few individual points of lighjt can be seen against the glow of unresolved stellar members."
11x80 binoculars show a faint small grouping of stars, not particularly well resolved, with a few brighter members. In the same field, to the north-east, lies a miniature southern Cross asterism.
A 15.5-inch telescope shows a rich starfield containing a large number of bright stars. Two bright stars shown just outside the cluster on the Uranometria chart lie to the east of a 9th magnitude star which marks the cluster. This 9th mag star is surrounded by a three-quarter circle of eight 11th magnitude stars. This arc appears to be in two parts; there are three dim stars forming a right-angled triangle around, and to the south of, the 9th magnitude star, and a westerly curve of stars starting north of this star. This cluster lies amidst a starfield of about six 8th magnitude stars.
16-inch f/10 SCT (102x, 290x)
Lovely in combination with two groupings. Busy western side and long string stretching out towards the NW and SE. The western side show off a extra long snake of stars as from the middle with a bend towards the north. Southern part of the cluster is more busy.
The Messier objects
The Bennett objects
The Caldwell list
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