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RA: 08h 13m 42s
Dec: −05° 45′ 0″
Ch: MSA:810, U2:275, SA:12
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 13r
Mag: B=6.11, V=5.8
This open cluster in Hydra was long believed to be a "missing" Messier object until astronomer Owen Gingrich linked it with NGC 2548.
Discovered by Caroline Herschel.
Synonyms: H VI-022
Recorded on December 7, 1786 by William Herschel with an 18.7-inch f/13 speculum telescope. He called it "a beautiful cluster of much compressed stars, considerably rich, 10 or 12' diameter. C.H. [Caroline Herschel] discovered it in 1783." In the Appendix to the 1912 'Scientific Papers of Sir William Herschel' M48 is discussed: "1790, March 5, Looked for the 48 of the Connoissance des Temps, but found that it does not exist in the place mentioned by Wollaston. I looked with the Sweeper .. and found a parcel of coarsely scattered stars, not deserving the name of a cluster; which on account of their being too far from each other could not be seen clustering in my 20 ft telescope. They are scattered over a place near 2 degrees in extent."
Trumpler (Lick Obs Bul, Vol 14, No. 420) gives the diameter as 30' and the class as 1 2 r.
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.
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Raab, S. (1922) A research on open clusters. Lund Medd. Astron. Obs. Ser. II, 28, 1.
Discussed, based of F-A plates.
Bailey, S.I. (1908) A catalogue of bright stars and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.
"A Catalogue of Estimated Parallaxes of 112 Nebulae, Open clusters and Star Groups", Vol 36 (4), p 107-115.
"irregular; well defined." He gives the approx. diameter as 42 arcmin.
The RNGC (Sulentic and Tifft 1973) notes that this is a 5.5 mag open cluster.
Listed by the Herschel Club, described as "large, bright nucleus with similar mag among stars. 8-inch, 48x."
Hartung notes: "A large field is needed for this bright open cluster, at least 30' across; the stars are numerous with many pairs, triplets and small groups which make a fine effect. Near the centre is a delicate close pair."
Kenneth Glynn Jones notes that many people can the see the cluster's glow with the naked eye.
Tom Lorenzin, in the electronic version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "5.8M; 40' x 25' extent; not so round, not so firm, not so fully packed (not a kilbasa!); uneven distribution of knots and strings; good binocular object!."
Houston notes that it has "a diameter about equal to that of the Moon and it can just be seen by the unaided eye when the sky conditions are right. My 5-inch apogee scope at 20x offers an excellent view of the cluster as it brings out a thinly scattered blanket of background stars."
WDS: cen pair prob = ADS 6672: m9.6,9.7; 6".8; pa207 (1960).
naked eye - faint patch, forming triangle w/zeta and triple of 1,c,2 Hya.
BS, 29Apr1992, TSP.
- mod f patch, almost consp once spotted. BS, 15Apr1993, Anderson
7x35mm - res cl elong SE-NW, fairly lg. about 20 *s res w/mod concen and many
widely-spaced outliers. two or three brtr *s aligned appox N-S at
center make "nuc". BS, 29Apr1992, TSP.
6cm - nice cl for sm scopes. well res w/60 *s. br *s run N-S through center
w/two or three pairs in it. center therefore appears elong. nicely
concen, though too loose to show it well.
7cm - br lg rich cl @ 30x w/consp string NE-SW through center. 20x shows that
outliers to N quad are prob in fld. concen, well-def part of cl 40'
diam w/broad concen except for dense cen string. 50x shows ~120 *s in
40' area. best overall view @ 30x. BS, 15Apr1993, Anderson Mesa.
15cm - lg, loose cl of 50 *s m8+ in 40' diam. tight circlet of *s twd center.
no cen condens. BS, 28Dec1970, FtL.
- fine 1.2deg fld. cl 45' diam but many outliers to N to 40' radius.
about 130 *s of m8+. nr center among brtr *s is nice faint pair: m11.5,
12; 7"; pa230. a few other pairs incl vun= one on N side. BS, 20Mar1988,
25cm - lg, br. 40' diam w/sev br pairs nr center. *s stragle to NW, size
60'x40'. 100 *s, m9+.
30cm - 100 *s in 40' diam. br *s in center run N-S. many pairs, loose (too
"This is a fine open cluster over one half of a degree in diameter, and easily seen in binoculars. It is composed primarily of fairly bright stars, loosely concentrated to the center. I estimated about 75 stars in the area."
Steve Coe, observing with a 17.5" f/4.5 at 100X, notes: "Somewhat scattered, Very Bright, can be seen naked eye, 12 stars are resolved in 8X50 finder, many chains of stars, little compressed, 7 *'s near center form an arch or boomerang shape. One * 9 mag orange at 60X. AZ city-- just naked eye, 12 stars in 11X80. 13" 60X (38mm Erfle)--bright, very large, pretty rich, little compressed, stars 9 to 13th mag. No fuzzy background, seems all stars are resolved. There are several chains and bright members. 61 stars counted in cluster.
Steve Coe (1992, The Deep-Sky Observer, Webb Society, Issue 1) observing with a 17.5-inch f/4.5 at 100x notes: "somewhat scattered, very bright, can be seen naked eye, 12 stars are resolved in 8x50 finder, many chains of stars, little compressed, 7 stars near centre form an arch or boomerang shape. One star 9th mag orange at 60x . . In my 5-inch binoculars, its shape appears distinctly triangular."
Danie Cronje, observing with 10x50 binoculars, calls it "quite large, quite bright. Individual stars can be resolved. Quite a large number of stars. In the middle of the cluster there is a brighter bar/wedge that stands out with averted vision. Quite beautiful."
This cluster is easy to find with hand-held 11x80 binoculars. It appears as a very delicate object, a matte cloud of starlight.
After hunting the faint galaxies in this region with a 10-inch f/5 with a 40mm eyepiece, it makes a pleasant change to happen upon this nice cluster. The shape defies definite classification, although it does appear to form a broad triangle lying northwest to southeast. I estimate at least 50-60 stars here. The cluster is pretty well spread out, the members forming no clear groupings other than a wedge-shaped knot of 13 stars in the cluster centre. This triangular asterism lies northeast to southwest, pointing towards the northeast.
(8-inch Meade, 18mm Super-Wide Angle eyepiece, 36' fov)
Very large, bright loose open expanded cluster. Stars forms circles and come together in pairs and triplets. Near the center to the north east of this cluster stars packet together. Mixed magnitude stars.
Alldays (22.50S, 20.12E, 770m).
12-inch f/10 SCT (76x, 95x, 218x)
Before my thoughts get out of hand let's continue to NGC 2548 (M48) and the constellation Hydra. Again, Caroline and Messier, independently discover this large, bright and loosely expanded cluster displaying circles, pairs and triplets. A prominent uneven string of stars runs through the cluster in an N to S direction (95x). Middle more condensed. High power bring out numerous outliers that mingle with the field.
2008 March 14, 20:20
Walmer, Port Elizabeth
2.5-inch f/7.6 refractor (EP: 12.5mm 56x 30arcmin fov)
Conditions: Unstable, Moon first quarter.
Size=55arcmin, V=5.8. Faint cluster, about 25 stars come into focus, of relatively equal brightness M8 to M9.5 (25mm eyepiece). Small dense chain running north-to-south M9.1 with bright glow of unresolved stars – focal point of cluster. Averted vision reveals dense chain about a magnitude brighter. NGC 2548 is a very big cluter, with dark empty spaces, and no prominent stars, however stars are well grouped in the 30arcmin field of view M8 to M9.5. Proved to be difficult to find, not visible through binoculars (8x20 and 16x32). Except for a few faint field stars, cluster is well detached: 28arcmin south two field stars M7.6 and M7.6, 20arcmin east three stars running south-to-north M7.2-M7.3.
Observing site: Little Tycho Observatory
[8h 13m 48s, -5° 48' 0"] This would be stunning in a dark sky, as it is, it's a nice washed out cluster of 30 8-10 mv stars with at least that many fainter ones close by.
Observing site: Little Tycho Observatory
[8h 13m 48s, -5° 48' 0"] A large, loose cluster, best at low power.
Observing site: Little Tycho Observatory
[8h 13m 48s, -5° 48' 0"] Appears sparse in these light polluted skies. There appear to be quite a few doubles in this cluster.
The Messier objects
The Bennett objects
The Caldwell list
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