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RA: 18h 15m 48s
Dec: −22° 08′ 0″
Ch: MSA:1392, U2:339, SA:22
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 12m
Mag: B=?, V=10
NGC 6583. See NGC 6573.
Synonyms: H VII-031
Discovered in 1786 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a cluster of vS and pretty compressed stars, considerably rich, 2' or 3' diameter."
Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "oblong cluster, not v rich nor v comp, but well insulated, stars 12m, 5' long, 4' broad."
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 3.8' and the class as 1 2 m.
The RNGC (Sulentic and Tifft 1973) notes that this is a 12.0 mag open cluster.
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "10M; 2' diameter; 35-plus 10M and dimmer members; small and condensed; looks like small, distant, poor GLOB; 1 degree SSE of 4M Mu SGR."
Steve Coe, observing with a 13" f/5.6, notes: "Pretty faint, pretty small, round, compressed, not rich, counted 12 stars at 220X."
1995-06-01: 11x80. Kelsey Farm. 23:00 SAST. I am not at all sure about this. I am looking at the exact position, and all I see is a _vast_ starcloud at least two degrees across, nothing seperately condensed and outlined I would call an open cluster.
Location: Jonkershoek Nature Reserve, Assegaaibosch Station
Date: 1998 July 31 / August 01, 01:00-02:40 SAST
11x80 tripod-mounted binoculars (9.5 mag stars at times not easy)
Sky conditions: Mediocre (transp. low, seeing average, dew) The skies are showing the effects of the combination of pollution (mainly from a nearby wood-processing plant) and a stable inversion layer, turning daytime skies grey-blue, and night skies ashen.
A tiny cluster that eluded me despite efforts to get its position spot-on.
The Messier objects
The Bennett objects
The Caldwell list
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