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RA: 19h 39m 59.4s
Dec: −30° 57′ 43.5″
Ch: MSA:1410, U2:379, SA:22
Ref: SIMBAD, SEDS
Type: globular cluster
Mag: B=8.12, V=7.42
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This globular was discovered by Lacaille and included in his 1755 catalogue as Class I No. 14. In his half-an-inch 8x telescope he saw it as being "like the obscured nucleus of a big comet."
Flammarion found it "plainly stellar... a huge agglomeration of stars uniformly distributed and immersed in a pale nebulosity. Diam. about 6' but a little elongated N-S This cluster should be admirable in the southern hemisphere; for us it is a little pale."
Messier could not find it in 1764 but succeeded in 1778, describing it as "a nebula which is a whitish spot; extending for 6' around the light is even and does not appear to contain a star."
In the Philosophical Transactions, 1818, William Herschel wrote: "1783, small 20 feet telescope. With 250 power fairly resolved into stars; I can count a great many of them, while others are too close to be distinguished separately. 1784, 1785, 20 feet telescope. A rich cluster of very compressed stars, irregularly round, about 8' long."
James Dunlop observed this object from Paramatta, New South Wales, and included it as No. 620 in his catalogue of 1827. Using a 9-inch f/12 telescope, he described it as "a beautiful, large round bright nebula, about 6' or 7' diameter, gradually condensed to the centre, easily resolvable."
Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "globular, pB, vL, R, vglbM, diam in RA 30 seconds; all resolved into separate stars 13..16m, not so comp M as to run together into a blaze or nipple." On a second occassion he called it "globular, a fine L, R, cluster, 6' diam, all clearly resolved into stars 11, 12, 13m, does not come up to a nipple."
Exploring the Southern Sky: A pictorial atlas from the European Southern Observatory. Springer-Verlag.
Scanned image on disk. [1987EtSS.........0L], plate 173.
Doig, P. (1925) Notes on the nebulae and clusters in Webb's 'Celestial Objects for Common Telescopes' (Sixth edition, Vol.ii). Part III. Southern Objects. M.N.R.A.S., 36(3), 91.
Bailey, examining a Bruce plate (Harvard Annals, Vol 72, No 2), describes it as "very remarkable, bright, globular cluster, pretty compressed, several hundred faint stars, diameter15'."
RA 19 39 59.4 (2000) Dec -30 57 44 Integrated V magnitude 6.32 Central surface brightness, V magnitudes per square arcsecond 19.13 Integrated spectral type F4 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster .76 Core radius in arcmin 2.83. ["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 7.0 mag globular cluster.
"! globular cluster, open"
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.
Burnham notes that "Early observers commented on the unusual openness of this cluster, and found the centre to be so little compressed that individual stars could be counted easily, with apparently blank sky in-between. This impression is due to the fact that only a relatively small percentage of the members exceed a brightness of 13th-14th magnitude, and the cluster does not begin to "fill in" until one reaches about 17th where a vast swarm of stars quite suddenly appears.
Harrington, P. (1986) An observer's guide to globular clusters. Sky&Telescope, Aug, 198.
.. the least condensed globular in Messiers catalgoue .. there are reports of it beign resolved with a 3inch bt this would seem a formidable task from midnorthern latitutdes. Low mag with a 8- or 10-inch separates many stars sprinkled across its nucleus. Such moderate-size scopes give the impression that M55 is very poorly populated. but most of its stars are 17th mag or fainter and not visible in average amateur telescvopes.
Gore, observing with a 3-inch refractor in India, saw "glimpses of stars in it with power 40X; it will not bear higher powers with this aperture".
It is easy to find in binoculars as a small faint haze, looking like a grossly unfocused star. In small telescopes, it appears as a 10' circular glow.
Hartung calls it "an open type of globular cluster nearly 10' across, irregularly round, rising only broadly towards the centre and beautifully resolved into stars scattered in a haze of fainter ones. Even 3-inch will show this to be a cloud of faint stars.
Stewart Moore (Fleet, Hampshire, UK), observing with a 12-inch f/5, writes in the The Webb Society Nebulae and Clusters Section Report No. 10, July 1992: "A difficult object to find. Visible as a uniform grey patch about 10' in diameter. Not resolved even at high power."
The mean blue magnitude of the 25 brightest stars, excluding the 5 brightest, is 13.68.
Steve Coe, observing with a 13" f/5.6, notes: "Bright, very large, irregularly round, very rich, somewhat compressed, little brighter in the middle. I counted 67 stars resolved at 165X. There are some dark lanes winding through the cluster."
Observer: Dave Mitsky; Your skills: Intermediate (some years); Date/time of observation: 06/19/98 05:40 UT; Location of site: ASH Naylor Observatory, Lewisberry, PA (Lat 40.1d N, 76.9d W, Elev 570'); Site classification: Exurban; Sky darkness: <5.0 Limiting magnitude; Seeing: 7 1-10 Seeing Scale (10 best); Moon presence: None - moon not in sky; Instrument: 17" f/15 equatorial classical Cassegrain; Magnification: 144x, 202x, 259x; Filter(s): None; Object(s): M55 (NGC 6809); Category: Globular cluster.; Class: 11; Constellation: Sagittarius; Data: mag 7.0 size 19.0'
Description: Located some 20,000 light years away, M55 is a very large and rich globular cluster that is about 81 light years in diameter. It is the least concentrated of the Messier globulars. M55's southerly location makes it a less imposing object in mid-northern latitudes than it is from southern climes. It was unresolved in the 5" f/5 finder scope. At 259x through the 17" M55 appeared as a large and "loose" globular that was roughly circular in shape. --
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "7M; 15' diameter; large and distinct though faint; resolved but grainily with 12M and dimmer members; little compressed center."
Location: Night Sky Caravan Farm, Bonnievale.
Date: 2016 Oct 30, Sunday.
Time: 22:25 SAST
Telescope: Little Martin (4-inch f/6.5 Celestron refractor)
45mm Celestron Plossl (15x): Very large swarm of almost invisible stars.
11mm Nagler Type6 (60x): Huge cluster in this field, very strongly mottled all across the disk.
Observing from Stellenbosch, 1983, I wrote: "This is an easy object to locate; I centered my 8x40 binoculars on Theta Sgr and moved downwards and I came across it. In my binos that night (rather hazy conditions) I noted it to be small and faint, looking more like a grossly unfocused star than a true globular. It reminds me of M4 as seen through thin clouds."
1997 July 9, Wednesday, 20:00 - 22:00 Jonkershoek. 11x80's tripod-mounted. Moderate conditions. Wow! A giant globular (at least 15' across) with a broad nucleus. Dominates the field of view.
Location: Campsite (South 23 16 East 29 26).
Sky conditions: Clear, steadiness good.
Instrument: Meade 8 inch, Super wide-angle, 18mm eyepiece; 36.2' fov
DSO Report N
Large, very clear bright, roundish globular cluster, gradually getting brighter to the middle with fringy edges. A haze of faint stars running out to the far edges. This cluster did not resemble the frosted look but instead a pale orange shade. About 15 arc minutes in size.
12-inch f/10 SCT (76x, 95x)
Could trace the 4 faint 13-magnitude stars on the south western edge in a sort of a line underline. Two thirds the way from W-E on the surface of the galaxy it is been broken off in haze with a small knot of haziness define it. It then slowly getting brighter and thicker again as it continues to the eastern edge. IC 1537 is well seen as a hazy out of focus uneven small patch. Two 9-magnitude star underline the galaxy below the south-western edge to high light the galaxy.
16-inch f/10 SCT (EP: 2-inch 40mm SW 102x 26' fov; 2-inch 32mm SW 127x 32' fov; 2-inch 14mm UW 290x 17' fov)
Breathtaking in its glory! Exhibited all the qualities, bright, large and round in form. With the 16" S/C and 101x magnification I can literally see through this open type of globular cluster. Mass of multitude stars. Getting slowly brighter to a soft roundish core. With averted vision it resembles sandpaper splintered in haziness. Around this globular the stars is been scattered to the far end of the field of view.
Sky Conditions:The fainter parts of the Milky Way are barely visible.Haziness only visible on the horizon.Atmosphere stable with little interference.
In this globular cluster the stars are very well resolved into 6th and 7th magnitude stars and that the stars in this cluster is slightly concentrated towards each other as a large diffuse mottled snowball.
In overall this globular cluster has an irregular appearance in contrast.This globular cluster measures 8.2'x 5.8'.Chart No:331,NSOG Vol.2.
Instrument:12-inch Dobsonian Reflector Telescope.
Sky Conditions:The fainter parts of the Milky Way are barely visible.
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.18(Extract taken out of "Atlas of the Night Sky").
Size:26mm Eyepiece:Field Of View:57'/7=8.1'.
20mm Eyepiece:Field Of View:50'/6=8.3'.
Size in Arc Minutes:8.2'(Nucleus).
Globular Cluster is 8.2'*4.1'.
Brightness Profile:From the central nucleus of this globular cluster it grows brighter than the outskirts.
Challenge Rating:Stunning Sight.
All the stars in this globular cluster are well resolved.By observing this cluster I have fount that the stars are slightly irregularly concentrated towards each other.In this cluster a bright chain of stars are seen radiating away from each other.I have also noted around the outskirts of this globular cluster there is some starless patches.
Telescope: 12” Dobsonian – f4,9. Eyepiece 15mm. FOV- 36’
Sky conditions: Seeing 3/5 (gibbous Moon)
Apparent size:18' x18'
Actual dimensions: 19' x19'(Cartes Du Ciel)
Globular cluster in Sagittarius
Roughly circular. Dim surface brightness overall.Edges diffuse. Nebulosity towards the S seems a bit brighter. Taking up half the fov
Slightly off center of the cluster, lines and arcs of bright stars form what looks like a sheriff’s badge/five pointed star with the brightest string of stars to the NW
The Messier objects
The Bennett objects
The Caldwell list
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