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RA: 17h 18m 24s
Dec: −42° 56′ 0″
Ch: MSA:1459, U2:408, SA:22
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 13m
Mag: B=6.32, V=6
Discovered by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "coarse B cluster VII. mainly inluded within an equilateral trinagle formed by 3 bright stars 5th and 6th mag. The N.f. of these taken." On a second occassion he called it "vL cluster VII class, of loose stars, on a very rich ground of small stars. The chief star, 6th mag, at the N.f. edge taken."
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 9' and the class as 2 3 p.
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 = 1.26 kpc."
The RNGC (Sulentic and Tifft 1973) notes that this is a 6.5 mag open cluster.
Steve Coe, observing with a 17.5" f/4.5 at 100X, notes: "Pretty bright, large, not compressed, pretty rich, 25 stars which are shaped like the bow of a ship at 100X. This is a very obscured region of Our Galaxy, there are many dark lanes nearby.
Observing from Stellenbosch, 1983, I saw this cluster in a 2-inch refractor as having a bright triangle of stars involved. No other stars easily visible. Three stars in the centre of the triangle difficult to resolved easily at low powers. Very poor and unimpressive -- observation made during strong moonlight. Estimated size as 10'.
One and a half degrees east of Eta Sco lies this interesting open cluster. 11x80 binoculars show here 3 similar-magnitude stars forming an equilateral triangle, with a fourth fainter star near the centre. One or two other stars are glimpsed outside the main triangular body.
24/09/93: 11x80 binoculars, strong moonlight: A nice equilateral triangle of stars; the bright moonlight washes out any other possible members.
1997 Sept 03: 11x80 tripod-mounted. 23:00 SAST. Jonkershoek. Clear, equilateral triangle, containing a tight knot of stars. Look for B263 due east.
1998-04-23/24, 11x80 tripod-mounted binoculars, Die Boord. Seeing good, transparency below average, dew. "
Just over a degree east of Eta Sco. While sweeping, appears as three bright (8th mag) stars plus haze. The three bright (white) stars form a neat 7' triangle, within which, especially near the southernmost star, are numerous vS companions. This grouping of large and small stars is noticeable even while scanning the region."
The Messier objects
The Bennett objects
The Caldwell list
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