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RA: 18h 31m 42s
Dec: −19° 07′ 0″
Ch: MSA:1367, U2:340, SA:22
Ref: SIMBAD, Collinder (1931), DAML02, Archinal&Hynes (2003)
Type: open cluster, 33m
Mag: B=5.29, V=4.6
IC 4725 = M 25. This is also one of Solon Bailey's clusters, though he did not make the identity with M25 -- that was left to Dreyer. I've given positions for the core of the cluster, and also for a much larger, more extended "halo" which is probably the object recorded by Bailey.
Bode thought the cluster somewhat nebulous, and Rev. Webb (1893) called it "coarse and brilliant." Smythe wrote of it as "a loose cluster of large and small stars; the gathering portion of the group attains an arched form and is thickly strewn in the south where a pretty knot of minute glimmers occupies the centre, with much star-dust around."
It was discovered by de Cheseaux in 1746, and then by Messier in 1764, who called it "a cluster of small stars... the stars seen with difficulty in a 3.5-foot telescope. No nebulosity seen... diam 10'."
In the Appendix to the 1912 'Scientific Papers of Sir William Herschel' this object is described as "1783, July 30, 20 feet telescope, Very large stars and some small ones; I counted 70, and there are many more within no considerable extent."
"cluster, fairly condensed; diam 25'; 50 stars; mags 9-12."
Bailey, S.I. (1908) A catalogue of bright stars and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Mel 204: An open cluster of fairly bright stars. Resembles NGC 6494. Not in NGC; noted by Bailey. Possibly this is NGC 6647.
Mel 204: Discussed, Based on F-A plates.
"A Catalogue of Estimated Parallaxes of 112 Nebulae, Open clusters and Star Groups", Vol 36 (4), p 107-115.
Mel 204: "open cluster fairly bright stars; like NGC 6494l contains U Sagittarii." He gives the approx. diameter as 50 arcmin.
(Lick Obs Bul, Vol 14, No. 420) gives the diameter as 35' and the class as 4 3 r.
M25 is "a scattered galactic star cluster, a bright but not especially rich aggregation containing about 50 stars brighter than 12th magnitude, and perhaps several dozen fainter members."
writes of it as a "spectacular open cluster ... a rich congregation of stars, both bright and faint, scatters without apparent form across the field."
Lorenzin, in the electronic version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "6M; 20' diameter; 35-plus 6 thru 10M vari-colored members; sparse and unimpressive."
Coe, observing with a 13" f/5.6, notes: "(M 25) Very bright, very large, pretty rich and somewhat compressed. I counted 43 members at 60X, I could pick out 11 stars involved using the 11X80 finder. U SGR is a nice orange variable star on the west side of this cluster. There is a dark area of missing stars in the very center of the cluster."
An easy binocular object, it seems to consist mainly of 6 or so brighter stars embedded in a mass of fainter ones. In 11x80 binoculars, the starfield surrounding this cluster enhances the beauty of the object. With M25 in the centre of the field, the surrounding stars seem to form a spiral arch which spans two degrees across. The spiral starts at a pair of reasonably close, dim stars one degree due east of the cluster. From this pair it curves to the northwest for 1 degree, and then turns back towards the open cluster, forming a logarithmic curve which winds tightly into M25.
30/04/93: Observing with a 6-inch f/8.6 Newtonian at 52x, this cluster is coarse, bright and very very large - with outliers it fills a one-degree field comfortably; the central part is just under a degree across. The most condensed part is about 10' across. My overall impression is that of 2 short, parallel, irregular rows of stars, SW-NE, separated by a dark band. The tips of each tow are joined by a ragged looping line of stars, rather like the outline of a squat snow-man. I estimate the Trumpler class as II 3 R. The most condensed part of the cluster appears as 2 distinct, parallel bands of stars, divided by a broad dark strip, running SW to NE. The NW band of stars is more populous, containing in the centre a 9th mag red beacon, flanked on each side by a 10th mag star. To the SW of the red star is a small parcel of stars. The SE band is merely four 9..11th mag stars arranged linearly, flanking the dark strip. Apart from these two bands, there are about 25 stars down to 10th mag scattered about. Those to the NW seem to form an irregular, ragged loop - starting NE, looping North and joining up in the NW. The SE loop encompasses a somewhat smaller space. Using a higher power (186x) clearly shows the parcel of stars as a V-shaped grouping of 5 stars arranged to point southwest.
1995 May 26, 03:00. 11x80 binoculars. A neat cluster. Has two much brighter members, both appear reddish. These two stars form the eye of a log spiral of stars, radiating outwards in a clock-wise sense. The cluster is coarse, spread-out and made up of large and small stars. It is readily seen.
12-inch f/10 SCT (76x, 218x)
This open cluster show a few groupings of faint stars. The part to the north is richer and display a string shape. The middle is broken down with a few faint stars just to the south of it in a vertical line from east to west. The south grouping contain about 6 faint stars in a tri angle shape. A lovely cluster to sketch. The lovely outstanding 6.4 u Sagittari display a light orange colour.
2008 May 06, 23:40
Walmer, Port Elizabeth
2.5-inch f/7.6 refractor (EP: 12.5mm 56x 30arcmin fov)
Conditions: Thin, hardly visible cirrus cloud over the area.
Size=32arcmin, V=4.6. Similar in appearance to Ptelmy's cluster; a large well-populated cluster with about 30 stars featuring a red/orange cast central prominent star M6.6. The remaining prominent stars range from M6.0-M7.4. All reasonably similar in birghtness forming the skeleton of the cluster, another orange/red star in the southwest part of the cluster M6.0, the remainder of the stars are all bluish/white. Coarse stars are of the 8th mag. Concentration of ten stars M6.6 to M9.1 in the western region of the belt running east-west in the centre of the cluster. Cluster is well spaced in the remaining areas with starless patches. Location was made less challenging by two field stars in close proximity to the cluster: 19arcmin south-southwest M4.5 HD 170433 a red/orange star and 31arcmin south M4.0 HD 170680.
Instrument:12-inch Dobsonian Reflector Telescope.
Sky Conditions:The fainter parts of the Milky Way are barely visible on the horizon.
Transparency of the Sky:Haziness only visible on the horizon.
Seeing:Atmosphere stable with little interference.
Object Type:Open Cluster.
First Impression:This object looks like an open cluster.
Chart Number:No.12(Extract taken out of "Atlas of the Night Sky").
Size:26mm Eyepiece:Field Of View:57'/9= 6.3'.
20mm Eyepiece:Field Of View:50'/8= 6.2'.
6.3'+ 6.2'= 12.5'.
Size in Arc Minutes:6.2'.
Open Cluster is 6.2'* 3.1'.
Brightness Profile:The central outskirts of this cluster grows brighter compared to the far outskirts of this cluster.
Challenge Rating:Very Easy.
The stars in this open cluster is well detached and this cluster is large because I have counted 180 stars within a fixed diameter.The stars range in brightness from magnitude 5 to 6. In overall most of the stars are nearly the same brightness as each other.The stars are however slightly concentrated towards each other.I have found a Cepheid variable star U Sgr which can range in brightness from magnitude 6.3-7.1.
Observing site: Little Tycho Observatory
[18h 31m 36s, -19° 15' 0"] A large, loose cluster of 6-12mv stars.
The Messier objects
The Bennett objects
The Caldwell list
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