Discovered by Charles Messier on June 5, 1764.
[from the description of M21:] The nearest neighboring known star to these two clusters is 11 Sagittarii, 7 mag, according to Flamsteed. The stars of both these clusters are of 8-9 magnitude, enveloped in nebulosity.
[Mem. Acad. for 1771, p. 443 (first Messier catalog)]
In the same night [June 5 to 6, 1764] I have determined the position of two clusters of stars which are close to each other, a bit above the Ecliptic, between the bow of Sagittarius & the right foot of Ophiuchus: the known star closest to these two clusters is the 11th of the constellation Sagittarius, of seventh magnitude, after the catalog of Flamsteed: the stars of these clusters are, from the eighth to the nineth magnitude, environed with nebulosities. I have determined their positions. The right ascension of the first cluster, 267d 4' 5", its declination 22d 59' 10" south. The right ascension of the second, 267d 31' 35"; its declination, 22d 31' 25" south.
[p. 456] 1764.Jun.5 RA: 267. 4. 5, Dec: 22.59.10.A. Cluster of stars a little above the Ecliptic, between the bow of Sagittarius & the right foot of Ophiuchus.
IV.41. May 26, 1785.
"A double st[ar]. with extended nebulosity of different intensity. About the double st[ar]. is a black opening[,] resembling the neb[ula]. in Orion in miniature."
[1811: PT Vol. 1811, p. 226-336; here p. 278]
3. Of Nebulosities joined to Nebulae.
The nature of diffused nebulosities is such that we often see it joined to real nebulae; for instance of this kind we have the following fourteen objects [including H IV.41 = M20] ..
Of treble, quadruple, and sextuple Nebulae.
If it was supposed that double nebulae at some distance from each other would frequently be seen, it will now on the contrary be admitted that an expectation of finding a great number of attracting centers in a nebulosity of no great extent is not so probable; and accordingly observation has shewn that greater combinations of nebular than those of the foregoing article [Of double Nebulae at a greater Distance..] are less frequently to be seen. The following list however contains 20 treble, 5 quadruple, and 1 sextuple nebulae of this sort. (*) See treble nebulae. [including H V.10 = M20].
Among the treble nebulae there is one, namely H V.10 [M20], of which the nebulosity is not yet separated. "Three nebulae seem to join faintly together, forming a kind of triangle; the middle of which is less nebulous, or perhaps free of nebulosity; in the middle of the triangle is a double star of the 2nd or 3rd class; more faint nebulosities are following [to the East]."
[Unpublished Observations of Messier's Nebulae and Clusters.
Scientific Papers, Vol. 2, p. 652]
1783, May 3. Two nebulae close together, both resolvable into stars; the preceding however leaves some doubt, though I suppose a higher power and more light would confirm the conjecture. 10 feet, power 350: the instrument will not bear a higher power in this low altitude.
Sweep 32 (July 9, 1826)
RA 17h 51m 64.4s, NPD 113d 0m 41s (1830.0)
A careful drawing taken, but the neb is not clear from twilight and clouds. (N.B. This drawing is unfortunately lost, and that engraved in fig. 80 is constructed from much less elaborate sketches, aided by memory.)
Sweep 30 (July 1, 1826)
RA 17h 51m 64.3s, NPD 113d 0m 6s (1830.0)
vL; trifid, three nebulae with a vacuity in the midst, in which is centrally situated the double star Sh 379, neb == 7' in extent. A most remarkable object.
very large; trifid, three nebulae with a vacuity in the midst, in which is centrally situated the double star Sh 379, the nebula is 7' in extent. A most remarkable object.
Sweep 31 (July 7, 1826)
RA 17h 51m 64.3s, NPD 113d 0m 43s (1830.0)
Seen in its place, but clouds prevented observation.
Sweep 588 (May 24, 1835)
RA 17h 52m 6.6s, NPD 113d 1m 32s (1830.0)
One of the most remarkable nebulae, and must be very carefully delineated. It is very large, and has many outlying portions and sinuses. See fig. 2, Pl. II.
[Drawing on Plate I in Mem.R.A.S. XXXIII (33)]
Vol. VIII of the Annals of the Observatory of Harvard College, which was received at Birr Castle in the summer 1877, contains lithographs from drawings by Mr. Touvelot of the following Nebulae: GC 116 [M 31] (Pl. 33), 1179 [M 42] (Pl. 24, Woodbury type), 4230 [M 13] and 4294 [M92] (Pl. 25), 4355 [M20] (Pl. 32), 4447 [M57] (Pl. 34), 4532 [M27] (Pl. 35).
Last Modification: February 20, 2005