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RA: 06h 28m 1.1s
Dec: −04° 50′ 51″
Ch: MSA:275, U2:227, SA:11
Ref: SIMBAD, Collinder (1931), DAML02, NGC/IC, Archinal&Hynes (2003)
Type: open cluster, 32p
Mag: B=?, V=4.2
Synonyms: H VIII-025
Discovered in 1785 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "The 10 Monocerotis surrounded by many bright stars."
Journal BAA, 35, Sep, p159.
A wide double star, yellow and orange, in elegant group.
Doig, P. (1925) Notes on the nebulae and clusters in Webb's 'Celestial Objects for Common Telescopes' (Sixth edition, Vol.ii). Part II. M.N.R.A.S., 35(8), 280.
The RNGC (Sulentic and Tifft 1973) notes that this is a 4.0 mag open cluster.
Houston calls this a "sprawling open cluster . . It contains about a score of stars spread across a Moon's diameter of sky. Since it shines with the combined light of a single 4th mag star, it can be glimpsed with the naked eye and is a beautiful object for binoculars. As the magnification increases, however, the cluster begins to disappear for lack of contrast with the background sky. As little at 50x with a 3-inch scope will soften the view a lot."
Listed by the Herschel Club, described as "naked eye object, very large, 20' in size, very striking stars, all bright with one blue-white star outstanding, seems to resemble a miniature Triangulum or Andromeda n appearance. 6-inch, 48x."
Ken Reeves, in "SACNEWS On-line for March 1997", observing with a 10-inch f/4.5 scope, notes: "NGC 2232 (06 26.6 -04 45) This is a confusing cluster, I saw about 20 stars including a bright central star, very bright, very large, pretty poor and not at all condensed. The brightest stars form a V shape pointing to the N. It is hard to tell what is the cluster as there are some other groups in the area, however this group is the most obvious and is at the location indicated in Uranometria 2000. Also with the background so rich, it is hard to tell where the cluster ends."
Steve Coe (Glendale, Arizona, USA) observing with a 13.1-inch f/5.6 reflector, writes in The Webb Society Nebulae and Clusters Section Report No. 11, January 1993: "Bright, very large, not compressed. Not rich when seen at x100. This scattered group of 22 stars includes 10 Mon."
Tom Lorenzin, in the electronic version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "4M; 30' diameter; sparse group including 5M star 10 MON; 20-plus 6 thru 8M members."
Steve Coe, observing with a 13" f/5.6, notes: "is bright, very large, not compressed and not rich at 100X. It is a scattered group of 22 stars including 10 Mon."
(8-inch Meade, 18mm Super-Wide Angle eyepiece, 36' fov)
Large, faint cluster. Stars form irregular wires to a half moon shape from northeast to northwest with a bright star to the north in this cluster.
Alldays (22.50S, 20.12E, 770m).
12-inch f/10 SCT (76x, 218x)
Large cluster, outstanding against the background star field. Stars form irregular wires to a half moon shape from N-S with the bright star Mon10 to the north in this cluster. Slightly elongated in this direction as well. The blue-white 10Mon show the way north with a member draping down south for more than 25' N-S. Fainter member dotted the western field of view. Lovely handful of stars quite open feeling.
Observing site: Little Tycho Observatory
[6h 26m 36s, -4° 45' 0"] A huge cluster ~2° across, of ~20 bright (6-8 mv) stars.
The Messier objects
The Bennett objects
The Caldwell list
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