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RA: 21h 30m 30s
Dec: +51° 35′ 0″
Ch: MSA:1087, U2:57, SA:9
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 22m
Mag: B=9.25, V=8.4
Synonyms: H VI-032
Discovered in 1788 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a beautiful cluster of pretty compressed stars 8' or 9' diameter, nearly round, considerably rich."
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 7.5' and the class as 1 2 m.
The RNGC (Sulentic and Tifft 1973) notes that this is a 11.5 mag open cluster.
Photo Index by Jim Lucyk: Observer's Guide (Astro Cards) 9-10/87 p28.
Houston notes: "easily picked up in my 5-inch moonwatch scope, this cluster appeared as an ill-defined loose scattering of stars, in a patch 9' to 12' across. Also, what resembles a still coarse cluster is almost tangent to the northwest." John Herschel mentions a red star in the cluster; this star is visual mag 10.2, and 28 of the stars in the cluster are brighter than mag 15.7.
Listed by the Herschel Club, described as "Counted 50 stars situated within this grouping. Very large and scattered. 8-inch, 48x."
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "9M; 8' diameter; 50-plus 11M and dimmer members; rich, faint and compressed."
6cm - nice & sm. 10-15 *s res against hazy bkgrnd. two brtst *s nr center in
15cm - sm mod f cl of 30 *s in a 10' area. only partially res @ 101x w/lg
surrounding haze 25' diam. fairly centrall condensed. BS, 2Jul1971, FtL.
- mod br fairly rich cl well detached from fld @ 50x, where it is
partially res with mod br haziness in core. 80x/140x: 6'-7' diam w/irreg
border, partic due to stragglers W & NW. brtst *s m11, lots coming in
around m13.5, lending to hazy/gran texture in 2'.5 core even @ 140x.
equal pair to W side outside cl. BS, 21Jun1991, Anderson Mesa.
25cm - med-sm and evenly concen. 10' diam w/40 *s. about a doz brtr members.
nice @ 90x.
30cm - 50 *s in sl concen cl. greatest concen on SE side, outliers spreading
N & W. more sharply bounded on NE to SE side. 15' N is a dk hole 25'
The Messier objects
The Bennett objects
The Caldwell list
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