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Lacaille I.12

Lacaille I.12, Messier 22, NGC 6656, Cl Melotte 208, C 1833-239, GCl 99, Bennett 114, h 2015, h 3753, GC 4424

RA: 18h 36m 24.21s
Dec: −23° 54′ 12.2″

Con: Sagittarius
Ch: MSA:1391, U2:340, SA:22

Ref: SIMBAD, SEDS

(reference key)

Type: globular cluster

Mag: B=7.16, V=6.17

Size: 32′
PA: ?

Image gallery

Sketches  (1)

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Photos  (3)

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Historical observations

Lacaille (1755)

Lacaille included it in his 1755 catalogue as Class I No. 12. In his half-an-inch 8x telescope he saw it as "a small comet nucleus."

Messier, Charles

Messier in 1764 described it as a "round nebula without stars, near 25 Sagittarii".

William Herschel (c.1784)

In the Philosophical Transactions, 1818, William Herschel wrote: "7 feet telescope. 460 has not light enough to show it; with 227 I see it very imperfectly. 1801, 10 feet telescope, with 600 it is a cluster of stars. 1783, small 20 feet telescope, with 350 power all resolved into stars. 1784, 20 feet telescope, an extensive cluster of stars. 1810, large 10 feet telescope, the stars are condensed in the middle, the diameter is 8', the greatest condensation is about 4'."

John Herschel (1847) Cape Observations

Observed by Sir John Herschel at the Cape of Good Hope with an 18-inch f/13 speculum telescope. He recorded it as "globular, vB, vL, vm comp, vgvmbM, 7' diameter. The stars are of two magnitudes, viz 15..16m and 12m; and what is very remarkable, the largest of these latter are visibly reddish; one in particular, the largest of all (= 12-11m) S.f. the middle, is decidedly a ruddy star, and so I think are all the other large ones." On a second occassion he called it "globular, fine, v rich, vm comp, gmbM, but not to a nucleus; diam in RA = 35.5 seconds; consists of stars of two sizes, 11 and 15m, with none intermediate, as if consisted of 2 layers, or one shell over another. A noble object."

John Herschel called it "a magnificent globular star cluster; gradually brighter in the middle but not to a nucleus. All the stars of two sizes: 10 and 11 mag, and 15 mag., as if one shell over another... larger ones ruddy."

Published comments

Melotte, P.J. (1915)

A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.

Burnham's Celestial Handbook

Discovery of this superb globular cluster is "usually credited to the obscure German astronomer Abraham Ihle in 1665; virtually nothing appears to be known about Ihle, however, and it has even been suggested that the name is a misprint for Hill", according to Burnham. He goes on to quote Smythe: ".. Hevelius, however, appears to have noticed it previous to 1665." Halley mentions it in 1716, and LeGentil observed it in 1747 in a telescope of 18-foot focal length, wherein it was seen as "very irregular, long-haired, and spreading some kind of rays of light all around its diameter".

Burnham's following comment deserves to be quoted in full:

"It has always seemed to the author of this book that J.R.R. Tolkein, in his delightful fantasy The Hobbit, unwittingly created an exquisite description of M22 when he spoke of the fabulous jewel called the "Arkenstone of Thrain": 'It was as if a globe had been filled with moonlight and hung before them in a net woven of the glint of frosty stars..."

Admiral Smythe spoke of it as "a fine globular cluster: consists of very minute and thickly condensed particles of light with a group of small stars preceding by 3 min. somewhat in a crucial form."

Doig, P. (1925)

Journal BAA, 36, Nov, p58

B parts nearly 15' diameter ... h;s impression of redness of the brighter stars is borne out by Shjapley's photogrpahic investigations of colour index in globular star clusters. Although some of the compoennts are vsiible with telescopes of modesrate dimensions, it is only the giants that are thuis seen.

Duncan, J.C. (1920)

Duncan, J. C. (1920) Bright nebulae and star clusters in Sagittarius and Scutum photographed with the 60-inch reflector. Astrophys. J., 51, 4-12.

Vorontsov-Velyaminov, B. (1925/1926)

Vorontsov-Velyaminov, B. "Integral magnitudes of south star clusters", Astron. Nach. 228, 325. Comparing the brightness of the cluster with the extrafocal images of stars, he estimates the magnitudes as 6.00

Harris, W.E. (1997)

RA 18 36 24.2 (2000) Dec -23 54 12 Integrated V magnitude 5.10 Central surface brightness, V magnitudes per square arcsecond 17.32 Integrated spectral type F5- Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 1.31 Core radius in arcmin 1.42. ["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) ]

Sulentic & Tifft (1973)

The RNGC (Sulentic and Tifft 1973) notes that this is a 6.5 mag globular cluster.

Bailey, S.I. (1908)

"!! globular cluster, fairly condensed"

Bailey, S.I. (1908) A catalogue of bright stars and nebulae. Ann.Harv.Coll.Obs., 60(8), 199.

Remarks, p.218: "a globular cluster somewhat resembling omega Centauri, NGC 5139. it contains 16 known variables"

Modern observations

Harrington, Phil (1986)

Harrington, P. (1986) An observer's guide to globular clusters. Sky&Telescope, Aug, 198.

..ranks as one of the heavens show pieces. 8inch will display many of the clusters 11th mag stars right across a fairly loose core. .. not perfectly round, and its east-west bulge can even be glimpsed in 20x80 binocs.

Hartung, E.J. (1968) Astron.Obj.South.Tel

M22 is one of the easiest globulars to resolve as the brightest members are 11th mag and within easy reach of an 8". Indeed, Hartung says a "3-inch shows the brighter ones quite plainly". Shapley found that this globular had an elliptical elongation in PA 25 degrees; there were 30% more stars along the major axis than along the minor axis. Hartung says the clusters "broad centre is about 7' across and the scattered outliers extend to 15'; it is a most beautiful object in a fine starry field..." On long-exposure photographs the overexposed nucleus appears irregularly round, and quite distinct from the outliers. Visually, this globular does not gradually grow dimmer towards the outside, but is very well concentrated with hardly any dimming to the outer edges -it is "all nucleus" This central concentration is irregular, with the stars forming streaked patterns.

Moore, S. (1992)

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 superb object and easily resolved to the centre. Gives the appearance of having three faint fingers of stars protruding from the W edge of the cluster."

Bortle, John (1976)

John Bortle (Webb Society Quarterly Journal, January 1976) using 10x50 binoculars, estimates the visual magnitude as 5.9.

Head, Marilyn

"10 Easy Globs!" by Marilyn Head (105 Owen Street, Newton, Wellington, Aotearoa / New Zealand; mhead@clear.net.nz)

"... the stars are more easily resolved. Indeed on one memorable night, the red and yellow stars in M22 reminded me far more of a jewel box than John Herschel's choice for that epithet - it was absolutely beautiful!"

Tom Lorenzin

Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "6M; 18' diameter; very open and uncondensed for a GLOB; well resolved 12M thru 13M stars against unresolved, diffuse glow; GLOB N6642 1 degree to WNW."

Ware, Donald J

Donald J. Ware:"Probably the finest globular cluster easily seen by observers at temperate northern latitudes. This cluster is about 15-20' in diameter, and is fairly easily resolved to its center. Many stars are seen in this rather loosely gathered globular cluster. This is a"must see" object."

Gramer, Lew (IAAC)

Observer: Lew Gramer; Your skills: Intermediate; Date and UT of Observation: 1997-07-4/5, 03:40 UT; Location: Savoy, MA, USA (42N, elev 700m); Site classification: rural; Limiting magnitude: 7.1 (zenith); Seeing: 5 of 10 - mediocre, increasing cumulus; Moon up: no; Instrument: Naked eye, 50mm Simmons binoculars; Magnification: 1x, 7x; Filters used: None; Object: M22, M28; Category: Globular clusters; Constellation: Sgr; Data: mags 5.2, 6.9 sizes 24', 11'; RA/DE: 18h30m -24o;

Description: M22 was barely spotted with the naked eye, in spite of its low altitude, 2o NE of lambda Sgr amid the background blur. M22 even in binoculars was a suprisingly LARGE, glittering ball of haze, with stellarings all the way around its edges, especially to the S and SW. Haze seemed to spray out from it in cluttered streamers to N, S, and W, merging with a pretty background of field stars & Milky Way haze. A yellowish star of about mag 8 was noted on its NE edge. Visible in the same binocular field with M22 were the much fainter globular M28, and the bright yellow star lambda Sgr. Intermediate between M22 and lambda was an apparent open cluster (no catalog #), a pretty clustering of stars mags 6 to 10. Closer still to lambda, the field stars appeared to attenuate somewhat. Then about 1/4 field NW of lambda, M28 was just visible as a spot of haze, showing loose concentration and no other detail.

Jakiel, Rich [s.a.a.]

From: jakiel@crl.com (Jennifer B. Jakiel)

Newsgroups: sci.astro.amateur

Subject: Ultimate Challenge: A PN in M22

Date: 29 Aug 1996 19:26:33 -0700

Last year at this time, I had asked if anyone had observed the exceedingly difficult planetary nebula in M22 known as IRAS 18333-2357. A number of seasoned observers have attempted to observe this object and as far as I know - there are no confirmed sightings. Last year I tried to observe this object with 18 and 20-inch scopes at high magnification and with UHC and O III filters but with no success.

The Challenge:

A positive sighting of faint PN IRAS 18333-2357 near the heart of M22.

Stats on the PN:

RA 18hr 33' 20.3"

DEC -23 degrees 57' 52"

size ~ 10" x 7"

Mag(v) ~ 15 (it may be considerably fainter..)

Viewing tips: Large aperture withexcellent optics are a must. I suggest at least 18 to 20" as a minimum. Magification must be *high* - at least 250 -300+, and seeing should be v. good or better. Apertures as large as 25-inches have been used with inconclusive results. This object is located close to the center of the giant globular and a clear separation from nearby stars is *difficult*.

The PN has a very good response to O III emissions, and using an UHC or esp. a H-Beta will be a waste of time. Megastar (and other programs) are highly useful in plotting postion as they should show the brighter stars in the globular.

It is good practice to try for Pease 1 (K 648) in M15 first. It is considerably brighter, though only ~ 1" across and responds well to filters and the "blink method". If you can't find Pease 1, don't bother with this other nasty!

Some refs:

Borkowski and Harrington, 1991. AJ 379 168

Gillet et al.,1989. ApJ 338 862

Please add coments to this thread on observation attempts, and good luck in hunting!

- Rich Jakiel

P.S....I plan to tackle this nasty once again down in the dark skies of Chiefland, Fla in October.

Steve Coe

Steve Coe, observing with a 13" f/5.6, notes: "(M 22) Very bright, very large, very rich, very compressed and much brighter in the middle at 135X. This magnificent globular has a blazing core and many streamers and coils of stars which make their way outward through the cluster. It is second only to Omega Centauri and 47 Tucana when it comes to globulars. I only got a short glimpse at 47 Tuc when I was in Austalia, but we got to study Omega Centauri near the zenith with a 12.5" f/6. M22 isn't quite that spectacular, but it is a close second."

[amastro] Observation of GJJC 1 in M 22

] Remember when Pease 1, the planetary nebula in M15, was considered an

] exotic find? More recently, amateurs took to hunting for GJJC-1, which

] resides in M22. I've still not seen that one, or know anybody who has. A

] paper published in late 1997 presents two more planetary nebulae in

] globular clusters.

Tom (and others) -

Bob Bunge and I were able to make an observation of GJJC 1 in 1997 (on August 3) using the Rupp Observatory (Mansfield, Ohio) 79-cm (31-inch) f/7 reflector. Gillett, et al., in their discovery paper, describe a pair of stars at the center of this planetary, with one of the components being the likely central star. This is shown on their illustration (figure 1a) as a single object. We were able to observe this as a slightly out-of-round object at 343x and 780x. It was found by locating the variable star ``V8'', as indicated on Plate I of Evans (MNRAS, 171, pp. 647-657, 1975), and then using the Gillett, et al. chart. A UHC nebula filter resulted in this pair becoming invisible. However, with no filter, moving one's eye on and off the merged pair showed an obvious ``blinking'' effect, which did not occur for nearby stars of the same brightness. This essentially confirmed that the central part of the planetary nebula - or at least its unusual ionizing star - was indeed observed. It is odd that Gillett, et al. do not report a similar blinking effect visually, but perhaps the brightness of the two stars overpowered this effect in the 3 meter telescope.

I attempted to repeat this observation in May at the TSP, using both Jay McNeil's 16-inch and Larry Mitchell's 36-inch. The stellar looking "double" was easily located in both 'scopes, but this time I could detect no obvious blinking effect (although as I recall Jay may have seen such an effect using a filter - perhaps he'd care to comment here). The difference, I suspect, is that the seeing at the TSP was very poor. As I recall it was quite good when observing with the Rupp reflector. This may explain why the object has been considered difficult to see and why Gillett, et al. didn't see it in the 3-meter - having good seeing in a large telescope is a relatively rare event.

I should add though, that in any of this observing, I was not able to detect the 12" or so diameter ring of the planetary itself.

Anyway, perhaps others out there with large aperture 'scopes can try observing this when they get a night of exceptional seeing and report their results.

Regards, Brent

[amastro] Re: Observation of GJJC 1 in M 22

Hi all,

Indeed, I am certain that I made a positive observation of GJJC 1 a few years back using similar apeture, power, and technique as described earlier by Brent A. A brief outline of the observation can be found on Doug Snyder's truly awesome PN website at blackskies.com. There is a great deal of general info concerning this particular PN located at this site also.

Jay McNeil

Contemporary observations

Auke Slotegraaf

1982

A 15.5-inch at 220 power clearly shows this; a dark starless lane, starting at the north-eastern edge of the nucleus, cuts across the northern quarter of the nucleus, creating the impression that the nucleus is roughly triangular in shape, with one apex pointing due west. Just south-east from this apex, to the south-west, extends a brief chain of stars, and a more spread-out chain radiates outwards from the southern point of the triangular nucleus. The angular appearance of the nucleus has been glimpsed with a 4.5-inch reflector at 45 power. The 15.5-inch at 220 power resolves this spectacular, large, pretty bright cluster easily, showing an unresolved central triangular nucleus containing some red stars. The apex of the triangular nucleus points inwards to the heart of the cluster, with the base of the triangle making up the edge. The two prominent star chains radiate out from the centre, parallel to the two sides of the triangle. With a 260x eyepiece, the appearance of a triangular core and two arms is still evident, but the 220x eyepiece showed a dark lane between the arms and the body of the triangle, whereas with the 260x eyepiece this impression is lost as stars are now seen in these lanes. The cluster bears magnification well, but at 260x I would describe it as a dense open cluster since it now appears very spread out, the stars scattered around the field. At 650x the arms dissolve into little clumpings of stars, but the triangular core defies resolution.

1997 October 27

1997 October 27: Jonkershoek, seeing 3, transparency 3, sky darkness 4, lim.mag. at south pole 6.0 (naked eye), 10.7 (binoculars). 11x80 tripod-mounted. "A brilliant cluster, flanked neatly by a right-angled triangle (containing a brilliant orange star 24 Sgr) and a parallelogram. With averted vision, the cluster appears to span about 10' of sky.

1993 April 30

30/04/93: Observing with a 6-inch f/8.6 Newtonian at 52x, this cluster is vL, vB and has a broad centre. The cluster has a drift time of at least 22 seconds (5') and appears mottled. At 104x small stars appear scattered across the main unresolved mass. I estimated its diameter at about 8' (fitting 3.5 times into the 12.5mm eyepiece field.)

1989

Lambda Sagittarius can be used to locate this fine object. As seen with 11x80 binoculars, Lambda is a bright reddish colour. It is flanked by two pretty bright 90 triangles of stars, one about two degrees to the northeast, another a degree south. The northeastern triangle has two slightly fainter stars inside its boundary. Just to the northeast of this triangle lies the large, 5th magnitude globular M 22. If one seeks out more geometric shapes in this area, one could say that M 22 also is flanked by two geometric figures; to its southwest is the afore mentioned triangle, whilst to the northeast lies a small parallelogram of four stars.

Magda Streicher

(no date)

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

Very large, round, beautiful, full field very bright star cluster. Spread out in trails and curves to a more elongated fringy edge. Faint compressed core, with some dark lane structure.

(no date)

12-inch f/10 SCT (EP: 2-inch 32mm SW 95x 42' fov; 2-inch 14mm UW 218x 23' fov)

One of the closest and most magnificent objects in the Milky Way that can be seen with the naked eye. Beautiful large, round, full field spectacular sight! Spread out in a multitude of stars, trails and curves to a more oval fringy edge (95x). Darker lines visible in the outer northern fringe. Faint compressed, wide core shows off a mass of faint star splinters. I presume the oval appearance might be attributed to stars that are densely grouped to the north that breaks up the round appearance. Brighter stars can be seen on the western periphery. Discovered in 1747 by Ihle.

Gary Lillis

2008 May 11

2008 May 11, 22:20

Walmer, Port Elizabeth

2.5-inch f/7.6 refractor (EP: 25mm 28x 45arcmin fov, 12.5mm 56x 30arcmin fov)

Conditions: Unstable, partly cloudy cumulus and strings of cirrus, becoming stable.

Size=24arcmin, V=5.1. Quite large, dim, just visibile. Small concentration toward the nucleus M9 visible at 28x. Globular is partially visible through 16x32 binoculars. Resolvability at times appears granular along with a small bar on the outer edge running southeast-northwest towards the nucleus, but could be an optical effect. NGC 6656 dims into background but to a degree is noticeable, not completely invisible. NGC 6656 has a 16arcmin halo with a 4arcmin nucleus. There are a fair number of field stars around NGC 6656 about five stars include 24 Sgr HD 17115 west 30arcmin M6.3-M8 and four stars east 33arcmin M5.9-M8.6.

Chris Vermeulen

2006 May 06

2006/5/6, 23h02

West Village, Krugersdorp

Sky Conditions: Moderate light pollution; Full Moon

Quality of Observation: Moderate

6" Dobsonian 25mm eyepiece

Description & Sketch: Although detectable with the naked eye M22 is not always easy to find due to its low location on the horizon and the ambient glow of city light attributes to the challenge in finding this object. With a 48x magnification it appeared circular and the dense core is probably the reason for its brightness. Stars in the core are clearly packed very tightly together as they could not be distinguished. It seemed like a huge bright ball in the centre of the object, and towards the outer edges of M22 there is very little fuzziness or cloudiness, as it seems to dissolve into the darkness rather suddenly. Maybe under better viewing conditions the cloudiness might appear visible. Furthermore in the outer edge it seemed there were a number of yellow-orange coloured stars as wells as white to white-blue coloured stars.

Richard Ford

2015, June, 21st

Location:Perdeberg.

Time:12:35am.

Sky Conditions:The fainter parts of the Milky Way are barely visible.Haziness only visible on the horizon.Atmosphere stable with little interference.

Instrument:12-inch Dobsonian.

This globular cluster has the shape of a large frozen out of focus snowball where the stars in this cluster is well resolved and that the stars in M22 are strongly concentrated towards each other as a tight halo of soft light.The nucleus of this globular cluster is loosely concentrated and that there is a large agglomeration of stars sprinkling out from this globular cluster.This globular cluster measures 8.2'x 5.8'.Chart No.329,NSOG Vol.2.

2010 July 3rd , Saturday

Location:Perdeberg.

Time:10:00pm.

Telescope:12"-inch Dobsonian Reflector Telescope.

Eyepieces:26mm super wide angle eyepiece.

20mm ultra wide angle eyepiece.

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.

Limiting Magnitude:4.5.

First Impression:Globular Cluster.

Location:Sagittarius.

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'.

8.1'+ 8.3'=16.4'.

16.4/2=8.2'.

Size in Arc Minutes:8.2'.

Size of nucleus vs.halo:7/8.2'=0.8'.

6/8.2'=0.7'.

0.8'+0.7'=1.5'.

1.5'/2=0.7'.

Size of Halo:0.7'.

Ratio:1:5.

Major Axis:8.2'.

8.2'/5=1.6'.

Minor Axis:1.6'.

Globular Cluster is 8.2'*1.6'.

Brightness:Extremely Bright.

Brightness Profile:High Surface Brightness.

Challenge Rating:An awesome sight under an extremely dark sky site under a very large telescope.

Description

-----------

This globular cluster is well resolved into a large agglomeration of bright stars slightly concentrated towards the center.This cluster is well defined and has an oval shape where the bright stars on the outskirts of this globular cluster is radiating slightly away from each other.This cluster has a uniform appearance of bright stars that is resolvable on the outskirts.It is actually concentrated as a large swarm of stars where I have found plenty of empty starless patches on the outskirts of this cluster.

Carol Botha

2010 -07 - 17

Location: Betty's Bay

Time: 22:00

Telescope: 12" Dobsonian f4,9. Eyepiece 15mm. FOV- 36'

Sky conditions: Seeing3/5 (gibbous Moon)

Apparent size:14'x 14'

Actual dimensions: 20 x20 (Cartes Du Ciel)

Object description:

Globular cluster in Sagittarius.

A whopper of a fuzzy patch of light in the finderscope!

Many stars resolved with strings of bright stars seemingly shooting from the core in all directions like a fireworks display.

The core does not appear brighter to the center.

Intriguing is the fact that in my sketch the nebulosity stretches beyond the fuzzy ball towards the SW, yet I did not describe this in my written obs. This will definitely have to be followed up in better seeing conditions.

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