sponsored by psychohistorian.org
RA: 18h 03m 24s
Dec: −27° 53′ 0″
Ch: MSA:1415, U2:339, SA:22
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 12rn
Mag: B=?, V=7.6
Synonyms: H VII-007
Discovered in 1785 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a considerably rich but pretty compressed, scattered cluster of stars, a little more compressed in the middle."
Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "a pretty compact cluster class VII of stars 9..13m; irregularly scattered, diam 4'."
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 4.5' and the class as 2 3 m.
Raab, S. (1922) A research on open clusters. Lund Medd. Astron. Obs. Ser. II, 28, 1.
Discussed, based of F-A plates.
The RNGC (Sulentic and Tifft 1973) notes that this is a 7.5 mag open cluster.
Photo Index by Jim Lucyk: Sky&Tel. 8/86 p130, Astronomy mag. 11/84 p11, Deep Sky #3 Su83 p8, Astronomy mag. 9/87 p50.
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Harrington writes: "With persistence, NGC 6520 can be seen as a faint smudge through 7x binoculars. Although a 4-inch telescope at low magnification shows a little more, higher powers and larger apertures are needed to unveil the cluster's true nature - a rich school of faint stars swarming in the stream of the Milky Way. In all, tiny NGC 6520 holds 60 stars within a 6' area."
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "9M; 5' diameter; small and dense; 25-plus 9 thru 12M members; DK NEB B-86 on W edge; cluster N6540 is 30' due E."
Steve Coe, observing with a 13" f/5.6, notes: "Pretty bright, pretty large, pretty rich, compressed, 22 members at 165X. There is a nice orange star in the center. Dark nebula B86 is distinct on the west side and the dark nebula and the cluster are about the same size."
Alldays (22.50S, 20.12E, 770m).
12-inch f/10 SCT (95x, 218x)
The larger part of this cluster forms a tight round inner section 3', which displays a round figure with faint stars. In a way it reminds me of a buffolo with his hornes, both hornes going west one from the north the other from the south extending away from this grouping.
The Messier objects
The Bennett objects
The Caldwell list
DOCdb is still in beta-release.
Known issues, feature requests, and updates on bug fixes, are here:
Found a bug? Have a comment or suggestion to improve DOCdb? Please let us know!
DOCdb is a free online resource that exists to promote deep sky observing.
You could help by sharing your observations, writing an article, digitizing and proof-reading historical material, and more.
Everything on DOCdb.net is © 2004-2010 by Auke Slotegraaf, unless stated otherwise or if you can prove you have divine permission to use it. Before using material published here, please consult the Creative Commons Attribution-Non-Commercial-Share Alike 2.5 License. Some material on DOCdb is copyright the individual authors. If in doubt, don't reproduce. And that goes for having children, too. Please note that the recommended browser for DOCdb is Firefox 3.x. You may also get good results with K-Meleon. Good luck if you're using IE. A successful experience with other browsers, including Opera and Safari, may vary.