Messier 22

Discovered by Abraham Ihle in 1665.

Messier: M22.

June 5, 1764. 22. 18h 21m 55s (275d 28' 39") -24d 06' 11"
Nebula, below the ecliptic, between the head and the bow of Sagittarius, near a star of 7th magnitude, 25 Sagittarii, according to Flamsteed, this nebula is round, it doesn't contain any star, & one can see it very well in an ordinary telescope of 3.5-foot [FL]; the star Lambda Sagittarii served for determination [of its position]. Abraham Ihle, a German, discovered it in 1665, while observing Saturn. M. Le Gentil observed it in 1747, & he made an engraving of it. Memoirs of the Academy, year 1759, page 470. Seen again March 22, 1781; it is reported in the English Atlas. (diam. 6')

[Mem. Acad. for 1771, p. 444 (first Messier catalog)]
In the same night of June 5 to 6, 1764, I have observed a nebula situated a bit below the ecliptic, between the head & the bow of Sagittarius, near the star of seventh magnitude, the twenty-fifth of that constellation, according to the catalog of Flamsteed. That nebula didn't appear to me to contain any star, although I have examined it with a good Gregorian telescope which magnified 104 times: it is round, & one sees it very well with an ordinary [non-achromatic] refractor of 3 feet & a half; its diameter is about 6 minutes of arc. I have determined its position by comparing with the star Lambda Sagittarii: its right ascension has been concluded as 275d 28' 39", & its declination as 24d 6' 11". It was Abraham Ihle, a German, who discovered this nebula in 1665, when observing Saturn. M. le Gentil has examined it also, & he has made an engraving of the configuration in the volume of the Memoirs of the Academy, for the year 1759, page 470. He observed it on August 29, 1747, under good weather, with a refractor of 18 feet length: He also observed it on July 17, & on other days. "It always appeared to me," he says, "very irregular in its figur, hair & distributing in space of rays of light all over its diameter."
[p. 456] 1764.Jun.5. RA: 275.28.39, Dec: 24. 6.11.A, Diam: 0. 6. Nebula without stars, between the bow & the head of Sagittarius.

Halley (1716): No. 3, Nebula in Sagittarius

[in Phil. Trans. XXIX, 390 (1716)]
The third is near the Ecliptick between the Head and Bow of Sagittarius, not far from the Point of the Winter Solstice. This it seems was found in the Year 1665 by a German Gentleman M.J. Abraham Ihle, whilst he attended the Motion of Saturn then near its aphelion. This is small but very luminous, and emits a Ray like the former. Its Place at this time is [Capricorn] 4 deg 1/2 with about half a Degree South Lat.

De Chéseaux: De Ch. No. 17.

A third, discovered by Abraham Ihle, between the head and the bow of Sagittarius, for which I found the RA of 275d 14' 10" and the southern declination of 24d 5' 30". It is 5' in diameter, it is round, of reddish color, instead of the yellowish of the Andromeda Nebula and the transparent of that in Orion.

Lacaille: Lac. I.12.

18:21:19, -24:05:00.
It resembles the preceding [Lac I.11, probably not M69].
[1763] Observed on April 6, 1752

Fortin

1774. [Position marked on Chart 9 and Chart 20.]

1795. [Position marked on Chart 9 and Chart 20.]

Bode: Bode 57.

A rather vivid nebula.

Koehler: Koehler No. 1

In the bow of Sagittarius, longitude 9s 5d 10' [275d 10']; approximate latitude 1d 0' south.

William Herschel

[PT 1800, p. 73-74. Reprinted in: Scientific Papers, Vol. 2, p. 45]
July 4, 1783. I viewed the nebula between Flamsteed's 25 and 26 Sagittarii, discovered by Abraham Ihle, in 1665 [M 22 = NGC 6656].
"With a small 20-feet Newtonian telescope, power 200, it is all resolved into stars, that are very small and close. There must be some hundreds of them. With 350, I see the stars very plainly; but the nebula is too low in this latitude for such a power."
July 12, 1784. I viewed the same nebula with a large 20-feet Newtonian reflector, power 157. "A most beautiful extensive cluster of stars, of various magnitudes, very compressed in the middle, and about 8' in diameter, besides the scattered ones, which do fill the extent of the field of view [This field, by the passage of an equatorial star, was 15'3"]: the large stars are red; the small ones are pale red. R.A. 18h 23' 39"; P.D. 114d 7'."
The penetrating power of the first instrument was 39, that of the latter 61; but, from the observations, it is plain how much superior the effect of the latter was to that of the former, notwithstanding the magnifying power was so much in favour of the instrument with the small penetrating power.

[PT 1818, p. 441. Reprinted in: Scientific Papers, Vol. 2, p. 597]
The 22nd of the Connoissance. [M 22 = NGC 6656]
"1783, 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, 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' 0"; the greatest condensation is about 4'0"."
By the observation of the 10 feet telescope, the profundity of this cluster must be nearly of the 344th order. It is near the following branch of the milky way.

John Herschel (1833): h 2015.

h 2015 = M22.
Sweep 30 (July 1, 1826)
RA 18h 25m 59.1s, NPD 114d 1m 16s (1830.0) [Right Ascension and North Polar Distance]
A magnificient globular cluster; gbM but not to a nucleus. The stars from 12 to 20 m. Those 12m are equally scattered over it, but those of 20m form the central mass.
A magnificient globular cluster; gradually brighter toward the middle, but not to a nucleus. The stars from 12 to 20m. Those of 12m are equally scattered over it, but those of 20m form the central mass.

Sweep 275 (July 28, 1830)
RA 18h 25m 61.2s, NPD 114d 1m 11s (1830.0)
A superb, v m comp, R cluster. Stars 11..15m; not very well defined. Rather more comp to the n f side than at centre; admirably seen in twilight.
A superb, very much compressed, round cluster. Stars of 11th to 15th magnitude; not very well defined. Rather more compressed to the north following [NE] side than at the centre; admirably seen in twilight.

Smyth: DCLIV [654]. M22.

DCLIV. 22 M. Sagittarii.
AR 18h 26m 25s, Dec S 24d 01'.4
Mean Epoch of Observation: 1835.57 [Jul 1835]
[with drawing]
A fine globular cluster, outlying that astral stream, the Via Lactea [Milky Way], in the space between the Archer's head and bow, not far from the point of the winter solstice, and midway between Mu and Sigma Sagittarii. It consists of very minute and thicky condensed particles of light, with a group of small stars preceding by 3m, somewhat in a crucial form. Halley ascribes the discovery of this in 1665, to Abraham Ihle, the German; but it has been thought this name should have been Abraham Hill, who was one of the first council of the Royal Society, and was wont to dabble with astronomy [This thought is probably spurious]. Hevelius, however, appears to have noticed it previous to 1665, so that neither Ihle nor Hill can be supported [Evidence for this appearance is low, in particular as Ihle and Hevelius were probably in good contact].
In August, 1747, it was carefully drawn by Le Gentil, as seen with an 18-foot telescope, which drawing appears in the Mémoires de l'Académie for 1759. In this figure three stars accompany the cluster, and he remarks that two years afterwards he did not see the preceding and central one: I, however, saw it very plainly in 1835. In the description he says, "Elle m'a toujours parue tres-irrégulière dans sa figure, chevelue, et rependant des espèces de rayons de lumière tout autout de son diamètre." This passage, I quote, "as in duty bound;" but from familiarity with the object itself, I cannot say that I clearly understand how or why his telescope exhibited these "espèces de rayons." Messier, who registered it in 1764, says nothing about them, merely observing that it is a nebula without a star, of a round form; and Sir William Herschel, who first resolved it, merely describes it as a circular cluster, with an estimated profundity of the 344th order. Sir John Herschel recommends it as a capital test for trying the space-penetrating power of a telescope.
This object is a fine specimen of the compression on which the nebula-theory is built. The globular systems of stars appear thicker in the middle than they would do if these stars were all at equal distances from each other; they must, therefore, be condensed toward the centre. That the stars should be accidentally disposed is too improbable a supposition to be admitted; whence Sir William Herschel supposes that they are thus brought together by their mutual attractions, and that the gradual condensation towards the centre must be received as proof of a central power of such kind.

John Herschel (1847): h 3753.

h 3753 = M. 22 = h. 2015.
Sweep 793 (June 27, 1837)
RA 18h 26m 4.1s, NPD 114d 2m 13s (1830.0) [Right Ascension and North Polar Distance]
Glob. Cl.; v B; v L; v m comp; v g v m b M; 7' diam. The stars are of two magnitudes, viz., 15..16 m, and 12 m; and what is very remarkable, the largest of these latter are visibly reddish; one in particular, the largest of all (= 12.11 m) s f the middle, is decidedly a ruddy *, and so I think are all the other large ones.
Globular Cluster; very bright; very large; very much compressed; very gradually very much bbrighter toward the middle; 7' diameter. The stars are of two magnitudes, viz., 15..16 m, and 12 m; and what is very remarkable, the largest of these latter are visibly reddish; one in particular, the largest of all (of 12 or 11 m) south following the middle, is decidedly a ruddy star, and so I think are all the other large ones.

Sweep 474 (July 29, 1834)
RA 18h 26m 4.6s, NPD 114d 2m 7s (1830.0)
Glob. Cl.; fine; v rich; v m comp; g m b M, but not to a nucleus; diam in RA = 35.5s; consists of stars of two sizes, 11 and 15, with none intermediate, as if it consists of two layers, or one shell over another. A noble object. [N.B. - Comparing this place with h 2015, a suspicion of proper motion arises.]
Globular Cluster; fine; very rich; very much compressed; gradually much bbrighter toward the middle, but not to a nucleus; diameter in RA = 35.5s [8.9']; consists of stars of two sizes, 11 and 15mag, with none intermediate, as if it consists of two layers, or one shell over another. A noble object.
[the conjecture in the "N.B." is not true - hf]

John Herschel, General Catalogue: GC 4424.

GC 4424 = h 2015 = h 3753 = M22.
RA 18h 27m 52.1s, NPD 114d 0' 25.8" (1860.0) [Right Ascension and North Polar Distance]
!!; Glob. Cl.; vB; vL; R; vRi; vmC; st 11...15 10 observations by W. & J. Herschel.
Very remarkable; globular cluster; very bright; very large; round; very rich; very much compressed; stars from 11th to 15th magnitude.

Dreyer: NGC 6656.

NGC 6656 = GC 4424 = h 2015 = h 3753; J.A. Ihle 1665, M 22, Lac I.12.
RA 18h 27m 51s, NPD 114d 1.0' (1860.0) [Right Ascension and North Polar Distance]
!!, Glob. Cl., vB, vL, R, vRi, vmC, st 11...15; = M22
Very remarkable, globular cluster, very bright, very large, round, very rich, very much compressed, stars from 11th to 15th magnitude.

Curtis

[Descriptions of 762 Nebulae and Clusters photographed with the Crossley Reflector. Publ. Lick Obs., No. 13, Part I, p. 9-42]
NGC 6656, RA=18:30.3, Dec=-23:59. M. 22. A beautiful globular cluster, 12' or more in diameter. 0 s.n.