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RA: 19h 55m 18s
Dec: +12° 07′ 36″
Ch: MSA:1243, U2:207, SA:16
Ref: SIMBAD, DAML02
Type: open cluster
Mag: B=?, V=10
NGC 6840 and NGC 6843 are two sparce clusters found by JH. N6840 has two groups of seven stars (separated by about 5 arcmin) in its core, surrounded by about 5-6 others. The stars are of fairly equal brightness, all being around 11th to 12th magnitude, and cover an area of 10 arcmin by 8 arcmin. N6843 is poorer with only around a dozen stars, again 11th to 12th magnitude, scattered over a smaller area.
Both are superposed on rich Milky Way backgrounds, so I'm not surprised that they did not stand out enough to be identified for RNGC. In fact, neither may be a real cluster, but proper motions and photometry could tell us that.
Synonyms: H VIII-019
Discovered in 1784 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a cluster of coarsely scattered large stars, not rich."
The RNGC (Sulentic and Tifft 1973) notes that this is a nonexistent object. Their coded description reads NOCL S.
16-inch f/10 SCT (127x 290x)
Only with a low power eyepiece could I make out a grouping if we can call it one. It appears as a few magnitude 11-13 stars in a very elongated shape from north-east to south-west in a relatively straight line that is somewhat outstanding.
The Messier objects
The Bennett objects
The Caldwell list
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