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RA: 19h 11m 12.06s
Dec: +01° 01′ 49.7″
Ch: MSA:1293, U2:251, SA:16
Ref: SIMBAD, SEDS
Type: globular cluster
Mag: B=11.37, V=9.78
This 9th magnitude 7' globular cluster was discovered by Hind on March 30, 1845. It is described in the NGC as "pretty bright, pretty large, very gradually a little brighter in the middle." Dreyer notes that it was suspected of variability, but concludes that there is no reason for thinking it variable, as the cluster "has little or no condensation, which probably makes its appearance more depending on the state of the atmosphere than would otherwise be the case."
RA 19 11 12.1 (2000) Dec +01 01 50 Integrated V magnitude 8.88 Central surface brightness, V magnitudes per square arcsecond 18.79 Integrated spectral type G5 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 1.59 Core radius in arcmin .33. ["Catalog Of Parameters For Milky Way Globular Clusters", compiled by William E. Harris, McMaster University. (Revised: May 15, 1997; from http://www.physics.mcmaster.ca/Globular.html; Harris, W.E. 1996, AJ, 112, 1487) ]
The RNGC (Sulentic and Tifft 1973) notes that this is a 11.0 mag globular cluster.
Included in a list of doubtful objects;. A faint, sparse loose cluster in a rich region.
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Steve Coe, in "SACNEWS On-line for September 1996", observing with a 13-inch, notes: NGC 6760 is a nice globular cluster. I saw it as bright, pretty large, round and somewhat brighter middle at 100X. I resolved 4 stars at 270X, but the globular is grainy at all powers. I estimate its magnitude as 10.5, size as 5 arc minutes. This cluster is located at 19 hr 11.2 min and +01 02.
Hartung notes that "it is about 2' across with little central condensation and some very faint stars can be made out with 30cm, while 15cm shows only a dim round haze."
Sanford notes that this "small globular cluster (2') .. is located a little less than 2 west of 23 Aquilae, and is about 11th magnitude. It is obscured by the dust of the Galaxy to a considerable extent."
Steve Coe, using a 13" f/5.6, notes: "Bright, pretty large, round, somewhat brighter middle at 100X. I resolved 4 stars at 270X, but the globular is grainy at all powers. I estimate its' magnitude as 10.5, size as 5 arc minutes."
AJ Crayon, using an 8" f/6 Newtonian, notes: "is a globular cluster that is 10m and 3' at 120x. It has a 13m star 1' to the nortwest.
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "11M; 2' diameter; round glow with little brighter center; not resolved at any power."
On this same night, I was surveying some objects in Aquila, including a couple that Brian mentioned. I noted that NGC 6760 (which Brian described using the 70mm Pronto) was easily visible in my 11x80mm finderscope. Through the 20-inch at 250x from a not-so-dark site near San Diego, it appeared 4' across with very broad concentration. I only noted several dozen stars resolved across the face. The brightest stars in NGC 6760 (from http://www.ngcic.com/papers/gcdata.htm) are tabulated as V=15.6. I had the same impression of NGC 6755 as a non-cluster. I saw about 60 stars mostly in two groups of widely varying brigtness between 10th and 14th magnitude. The northern group may be Cz 39. Centered in the southern grouping is a tiny clump of five 12th-magnitude stars about in an area 30" across.
Aquila as a whole is interesting. The western half of the constellation is nothing but Milky Way planetaries and clusters, some of which are impressive. East of a line that connects Altair to Lambda Aquilae, these give way to very distant galaxies. In fact, there is nothing in this half of Aquila that would qualify as a showpiece on anybody's list.
Arizona Sky Pages
Subject: [amastro] Dwarfs in a dwarf telescope
I spent a bit more time last night (5 Sep UT) casting about with the Pronto at Anderson Mesa on another excellent post-monsoonal night. Among the targets were some low-surface-brightness Local Group dwarf galaxies: in decreasing order of brightness NGC 6822, IC 1613, and the Wolf-Lundmark-Melotte galaxy. At about mag. 9 and mean surface brightness about mag. 14.5/square arcmin, NGC 6822 was readily spotted at 30x. IC 1613, a magnitude fainter, was a marginal object, and WLM, somewhat fainter still by the specs, was apparently a bit too faint and I couldn't reliably see it. I'd like to try WLM again perhaps from a more southerly location.
In the field with NGC 6822 is the bright planetary NGC 6818. Since this was substellar at 30x, I estimated its brightness (without filters) with respect to the mag. 8 star west (HD 186107) as about 0.6 mag. fainter. This star has V=8.1, but is quite red, B-V=1.7, so assuming the 0.2(B-V) factor to get visual magnitudes, the planetary comes out right at mv=9.0, perhaps slightly brighter than Marling's mv=9.3. One might also make an estimate wrt the fainter star east (HD 186368, V=9.5/B-V=0.3), since its color is more neutral.
I also looked at NGC 6760 in Aquila. This was comfortably faint for the Pronto. The halo reaches roughly to a relatively bright star on the NE side of this cluster. This is mentioned by Luginbuhl & Skiff as mag. 10.5, but is actually mag. 12 or 12.5 (Kepple & Sanner also wrong.) This star was used by several 19th century observers (Winnecke, Lord Rosse, Bigourdan) as an astrometric reference; Bigourdan also calls it mag. 12 or 12.2 in two of his four observations.
While poking around near NGC 6760, I came across what appeared to be a large "absorption hole" starcloud and a tiny fuzzy knot half a degree north of it. After refinding it from 6760 with atlas in hand, I was surprised to learn that these were NGC 6755 (starcloud) and NGC 6756 (knot). NGC 6755, although a nice object at 30x, has what is to me a distinctly non-open-cluster appearance (luminosity function not right)---I'd be willing to bet this is nothing more than a starcloud. NGC 6756 was inscrutable, simply too small and faint for the Pronto at 60x.
15cm - easily found N of circlet @ 30x. 120x: round, 1'.5 diam. some gran with
three of four *s N. HM, Roof.
- 190x: 2' diam, gran at best. m11.5 * on NE side. BS, 3Sep1981, Anderson
- consp diff cl @ 50x. 3' diam, even concen @ 165x. a few m12-13+ fld *s
give impression of partial res. BS, 14May1988, TSP.
25cm - oval elong N-S @ 180x, 3'.5x2'.5, core 2'. NE is m10 *. gran to partially
res. nearby fld has few *s. BS, Roof.
- elong in pa75, consp m12.5 fld * is in pa45. circlet of brtr *s crudely
def. fld N has few f *s. BS, 20Aug1979, Slate Mtn.
- 190x: 3'.5 diam, brtr part 2' across. broad concen. some m13 *s over it.
partially res, much haze. N edge of cl more well def, giving impression
of E-W elong. BS, 3Sep1981, Anderson Mesa.
30cm - core broad, round. star 1' E. 2'.5 diam overall. a few outliers. NE 1'.5
is m9 *. CBL, Roof.
Instrument:12-inch Dobsonian Reflector Telescope.
Sky Conditions:The fainter parts of the Milky Way are barely visible with the naked eye.
Transparency Of The Sky:Haziness only visible on the horizon.
Seeing:Atmosphere stable with little interference.
Object Type:Globular Cluster.
First Impression:This object looks like a globular cluster.
Chart Number:No.12(Extract taken out of "Atlas of the Night Sky").
Size:26mm Eyepiece:Field Of View:57'/12= 4.7'.
20mm Eyepiece:Field Of View:50'/11= 4.5'.
4.7'+ 4.5'= 9.2'.
Size In Arc Minutes:4.6'(Nucleus).
Globular Cluster is 4.6'* 1.5'.
Brightness Profile:Towards the central nucleus of this globular cluster it grows slightly brighter compared to the far outskirts of it.
The stars in this globular cluster are unresolved and that this cluster looks like a very faint snowball.The stars in this globular cluster are too faint to show any resolution and that this cluster is centrally concentrated as a tight halo towards each other.
The Messier objects
The Bennett objects
The Caldwell list
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