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NGC 6451 (14,737 of 18,816)


oc gc pln bn dn gx gxcl ast aka lost




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Tom Thumb Cluster

NGC 6451, Cl Collinder 352, C 1747-302, Cl VDBH 250, Tom Thumb Cluster, VI 13, h 3707, GC 4335

RA: 17h 50m 42s
Dec: −30° 13′ 0″

Con: Scorpius
Ch: MSA:1415, U2:377, SA:22

Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)

(reference key)

Type: open cluster, 12rn

Mag: B=?, V=8.2

Size: 7′
PA: ?

Historical observations

William Herschel (c.1784)

Synonyms: H VI-013

Discovered in 1785 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a cluster of small and pretty compressed stars of several magnitudes, 5' or 6' diameter, not very rich."

John Herschel (1847) Cape Observations

Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "pretty rich, irregularly round, stars 13m, a cluster with a great black cut acorss it; 6' diameter, with many outliers." On a second occassion he called it "a remarkable cluster, divided into two by a broad vacant straight band, irregularly round, 8' diameter, stars 12..15m, See fig 6, Plate V." He also mentions this cluster in his comment on NGC 5128: "On the other hand we have, in the completely resolved cluster,[NGC 6451], an object which, removed to such a distance as to appear nebulous, would present a considerably approach to it in point of general aspect."

Published comments

Trumpler, R.J. (1928)

Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 6' and the class as 2 2 m.

Raab, S. (1922)

Raab, S. (1922) A research on open clusters. Lund Medd. Astron. Obs. Ser. II, 28, 1.

Discussed, based of F-A plates.

Sulentic & Tifft (1973)

(Sulentic and Tifft 1973) notes that this is a 8.5 mag open cluster.

Photo index

Photo Index by Jim Lucyk: Sky&Tel. 7/69 p58 (drawing by J. Herschel).

Melotte, P.J. (1915)

A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.

Modern observations

Walter Scott Houston (1969)

Houston, W.S. (1969) Deep-sky Wonders: NGC 6451. Sky&Telescope, July, 58.

discusses this object and its surroundings; Gerald B. Fifer's "keyhole" in Scorpius; sketch by Fifer and h.

Tom Lorenzin

Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "9M; 6' diameter; fairly large, rich and compressed; 50-plus 10 thru 13M members."

Steve Coe

Steve Coe, observing with a 17.5" f/4.5 at 100X, notes: "Bright, pretty large, pretty rich, compressed open cluster at 165X. It is bright enough that it can be seen in the 8X50 finder. It includes a close triple star which appears nebulous at low powers and is resolved at 320X. I estimated 50 members in the cluster and it includes a dark lane almost down the middle of the cluster.

Contemporary observations

Auke Slotegraaf


Observing with a 6-inch f/8.6 Newtonian at 52x, the cluster shows half a dozen or so 9..10m stars forming a dim, irregular grouping. There is either much unresolved haze inbetween the stars, or the optics are dewed.

Magda Streicher

(no date)

Alldays (22.50S, 20.12E, 770m).

12-inch f/10 SCT (95x, 218x)

Faint slightly round haze and care many faint stars involved. The cluster is sharp define towards the NW spraying out towards SE. A relatively long string can be seen hanging on the cluster on the west of the field of view. It looks like a double star towards the middle section.

Favourite lists

Lacaille's catalogue

The Messier objects

Dunlop's catalogue

The Bennett objects

The Caldwell list

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