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NGC 6991 (18,784 of 18,816)


oc gc pln bn dn gx gxcl ast aka lost




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NGC 6991

NGC 6991, VIII 76, h 2091, GC 4615

History and Accurate Positions for the NGC/IC Objects (Corwin 2004)

NGC 6991. WH and JH saw two different clusters; JH mistakenly included them in GC under a single number. Dreyer, of course, followed GC for the NGC. I've included both in the table, so you get to choose which one you want. Here are the stories to help you along:

WH describes his object as "A star 6 m surrounded by considerable stars forming a brilliant scattered cluster; the large star not in the middle, but following." His position is a couple of arcmin south of the bright star, but there is no mistaking the group that he saw. There is also some nebulosity on the preceding side of the cluster, but it is faint enough that neither of the Herschels saw it.

JH has two observations of his cluster, which is smaller, fainter, perhaps a bit richer, and southwest of his father's. The first reads, "A star 11 m. The last of that magnitude in an irregular triangular cluster 6' diameter; poor and straggling." His second, from his next sweep, says simply, "A star 9 m; the largest of a cluster." His positions point pretty accurately to the stars he mentions, and his cluster is just as clear as his father's. But -- just as clearly -- the two clusters are not the same.

Choose one if you wish. I'll take both.

Historical observations

William Herschel (c.1784)

Synonyms: H VIII-076

Discovered in 1788 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a star 6th mag surrounded by many considerable stars, forming a brilliant scattered cluster of large stars, not in the middle, but following."

Published comments

Sulentic & Tifft (1973)

The RNGC (Sulentic and Tifft 1973) notes that this is a open cluster.

Modern observations

Brian Skiff

15cm - no cl at U2000 location. BS, 17Jun1991, Anderson Mesa.

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