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Type: asterism?, p
Mag: B=?, V=?
Size: 2′ x 1′
NGC 5998 is probably not a cluster, but it is close to WH's position, and matches his description. It is so clearly seen on the IIIa-J film that I'm a bit surprised that both RNGC and ESO list it as not found. Still, the relevant information is not in NGC; WH's description reads, in full, "A cluster of very small stars, pretty rich, 6 arcmin long, 4 arcmin broad; in the form of a parallelogram." The parallelogram encloses about two dozen stars, half of which are in GSC. The center of the figure is about 2 arcmin northeast of WH's place, but that is well within his usual error for clusters.
Synonyms: H VII-029
Discovered in 1786 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a cluster of vS stars, pretty rich, 6' long, 4' broad, in the form of a parallelogram."
The RNGC (Sulentic and Tifft 1973) notes that this is a nonexistent object. Their coded description reads NOCL S.
At this years Texas Star Party I observed the "non-existent" open star cluster NGC 5998 in Scorpius. Using an 18" f/5 reflector at 163X ( 30' true field ) in choppy seeing, I found a detached scatter of nine 13th to 14th magnitude stars in a loose arrangement spanning about 3 arc minutes across. The immediate surrounding field appeared bland, making this cluster ( asterism? ) obvious.
According to Brent Archinal's "The "Non-Existent" Star Clusters of the RNGC" , William Herschel observed this cluster only once ( on April 30, 1786 ). Herschel described a "cluster of very small stars, pretty large, pretty rich, in the form of a parallelogram"- which betters my observation by a long shot- but I'm confident that this is the "missing" cluster... The position given in Sinnot's " NGC 2000.0" is 15 49.4 -28 36 - within a minute or so of the position of my detached group of stars.
Alldays (22.50S, 20.12E, 770m).
12-inch f/10 SCT (95x, 218x)
About 8 very faint 13magnitude stars in a slightly elongated N-S tight grouping. Very busy faint star field. In a way it looks like the big dipper or Delphinius shape.
The Messier objects
The Bennett objects
The Caldwell list
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