Messier 17

Discovered by Philippe Loys de Cheseaux in 1745-46.
Independently rediscovered by Charles Messier on June 3, 1764

Messier: M17.

June 3, 1764. 17. 18h 07m 03s (271d 45' 48") -16d 14' 44"
A train of light without stars, of 5 or 6 minutes in extent, in the shape of a spindle, & a little like that in Andromeda's belt [M31] but of a very faint light; there are two telescopic stars nearby & placed parallel to the equator. In a good sky one observes this nebula very well in an ordinary telescope of 3.5-foot [FL]. Seen again 22 March 1781. (diam. 5')

[Mem. Acad. for 1771, p. 442-443 (first Messier catalog)]
In the same night [June 3 to 4, 1764], I have discovered at little distance of the cluster of stars of which I just have told, a train of light of five or six minutes of arc in extension, in the shape of a spindle, & in almost the same [shape] as that in the girdle of Andromeda [M31]; but of a very faint light, not containing any star; one can see two of them nearby which are telescopic & placed parallel to the Equator: in a good sky one perceives very well that nebula with an ordinary [non-achromatic] refractor of 3 feet & a half [FL]. I have determined its position in right ascension of 271d 45' 48", & its declination of 16d 14' 44" south.
[p. 456] 1764.Jun.3. RA: 271.45.48, Dec: 16.14.44.A, Diam: 0. 5. Train of light without stars, little distant from the preceding star cluster.

De Chéseaux: De Ch. No. 20.

Finally, another nebula, which has never been observed. It is of a completely different shape than the others: It has perfectly the form of a ray, or of the tail of a comet, of 7' length and 2' broadth; its sides are exactly parallel and rather well terminated, as are its two ends. Its middle is whiter than the borders; I have found its RA for this year as 271d 32' 35" and its southern declination as 16d 15' 6". It has an angle [PA] of 50 deg with the meridian.

Bode: Bode 54.

A nebula.

William Herschel

[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 M17] ..

[Unpublished Observations of Messier's Nebulae and Clusters. Scientific Papers, Vol. 2, p. 652]
1783, July 31. A very singular nebula; it seems to be the link to join the nebula in Orion to others, for this is not without a possibility of being stars. I think a great deal more of light and a much higher power would be of service.
1784, June 22 (Sw. 231). A wonderful nebula. Very much extended, with a hook on the preceding [Western] side; the nebulosity of the milky kind; several stars visible in it, but they seem to have no connection with the nebula, which is far more distant. I saw it only through short intervals of flying clouds and haziness; but the extent of the light including the hook is above 10'. I suspect besides, that on the following [Eastern] side it goes on much farther and diffuses itself towards the north and south. It is not of equal brightness throughout and has one or more places where the milky nebulosity seems to degenerate into the resolvable [mottled] kind; such a one is that just following the hook towards the north. Should this be confirmed on a very fine night, it would bring on the step between these two nebulosities which is at present wanting, and would lead us to surmise that this nebula is a stupendous stratum of immensely distant fixed stars, some of whose branches come near enough to us to be visible as a resolvable nebulosity, while the rest runs on to so great a distance as only to appear under the milky form.

John Herschel (1833): h 2008.

h 2008 = M17.
Sweep 163 (July 19, 1828)
RA 18h 10m 44.2s, NPD 106d 17' 55" (1830.0) [Right Ascension and North Polar Distance]
The principle star in the preceding are of a horse-shoe-like portion of the nebula M17. See fig. 35.

Sweep 274 (July 27, 1830)
RA 18h 10m 46.8s, NPD 106d 14' 5" (1830.0)
The small insulated, resolvable knot in the preceding, strait branch of the nebula.

Sweep 358 (July 30, 1831)
RA 18h 10m 51.8s, NPD 106d 14' 19" (1830.0)
The same knot. See description of this neb in the Appendix. See also figure.

Sweep 33 (July 24, 1826)
NPD 106d 15' 48":: (1830.0)
A most curious object, not unlike the nebula in Orion (as it used to be figured, like a Greek capital Omega.) There is in it a resolvable portion or knot distinctly separated from and insulated in the rest as if it had absorbed the nebula near it. (A figure carefully drawn.) (The P.D. inaccurate, being much past merid.)

Sweep 48 (August 6, 1823)
NPD 106d 15' 27":: (1830.0)
A large extended nebula. Its form is that of a Greek Omega with the left (or following) base-line turned upwards. The curved (or horse-shoe) part is very F, and has many stars in it. The preceding base-line hardly visible. The following, which is the principle branch, occupies nearly half the field (7 1/2'.) Its light is not equable, but blotty. Strong twilight.

[Appendix]

[Figure on Plate XII, Figure 35, No. 2008, M. 17, RA 18h 10m 45s, NPD 106d 15']

Fig. 35. Mess. 17. - The figure of this nebula is nearly that of the Greek capital Omega, somewhat distorted and very unequally bright. It is remarkable that this is the form usually attributed to the great nebula in Orion, though in that nebula I confess I can discern no resemblence whatever to the Greek letter. Messier perceived only the bright preceding branch of the nebula now in question, without any of the attached convolutions which were first noticed by my Father. The chief peculiarities which I have observed in it are, 1st, the resolvable knot in the following portion of the bright branch, which is in a considerable degree insulated from the surrounding nebula; strongly suggesting the idea of an absorption of nebulous matter; and 2ndly, the much feebler and smaller knot in the north preceding end of the same branch, where the nebula makes a sudden bend at an acute angle. With a view to a more exact representation of this curious nebula, I have at different times taken micrometrical measures of the relative places of the stars in and near it, by which, when laid down on the chart, its limits may be traced and identified, as I hope soon to have better opportunity to do than its low situation in this latitudes will permit.

Smyth: DCXLV [645]. M17

DCXLV. 17 M. Clypei Sobieskii [now Sagittarii].
AR 18h 11m 23s, Dec S 16d 15'.8
Mean epoch of the Observation: 1836.68 [August 1836].
[with a drawing]
The horse-shoe, or Greek-omega Omega, nebula, just below Sobieski's shield; discovered by M. Messier in 1764, and registered as a train of light without stars, about 5' or 6' in extent. As with the two preceding objects [M16 and M18], its place hangs upon Mu Sagittarii, from which it bears north-by-east, about 5deg distant, in the line towards Epsilon Aquilae. In my telescope charged with a moderate [magnification] eye-piece, this curious nebula is well seen, though not to the extent of convolution figured by Sir John Herschel. A magnificient, arched, and irresolvable luminosity occupies more than one third of the area, in a splendid group of stars, among which are Nos. 38 and 43, Hora XVIII. of Piazzi; they are principally from the 9th to the 12th magnitudes, reaching more or less all over the field, somewhat in the accompanying form.

John Herschel (1847)

[Figure 1 on plate II]

Lord Rosse

John Herschel, General Catalogue: GC 4403.

GC 4403 = h 2008 = M17.
RA 18h 12m 33.1s, NPD 106d 13' 36.0" (1860.0) [Right Ascension and North Polar Distance]
!!!; B; eL; eiF; 2-hooked. 9 observations by W. & J. Herschel.
Magnificient; bright; extremely large; of extremely irregular shape; hooked like a "2" [number/digit "2"].
Remark: Figures in P.T. 33 [JH 1833], plate iv, fig. 35; C.G.H. [JH 1847], plate ii, fig. 1; Lam. [Dr. Lamont's "Oeffentliche Vorlesung über Nebelflecken", Munich 1837], plate i, fig 10; M.A.A. [Mr. Mason's Memoirs in vol. vii of the Transactions of the American Academy], plate vi, fig. 1.

Huggins

[Phil. Trans. Roy. Soc., Vol. 156 (1866), p. 381-397; here p. 385]
[No. [GC] 4403, 2008 h. 17 M. R.A. 18h 12m 33s. N.P.D. 106d 13' 36". Remarkable object. Bright; extremely large; extremely irregular figure; 2-hooked.]
Sir John Herschel observes of this nebula, "A most curious object, not unlike the nebula in Orion (as it used to be figured like a Greek capital Omega). There is in it a resolvable portion (*) or knot distinctly separated from and insulated in the rest, as if it had absorbed the nebula near it. Its form is like the Greek Omega, with the left (or following [Eastern]) base-line turned upwards. The curved or horseshoe part is very faint, and has many stars in it; the preceding [Western] base-line hardly visible. Its light is not equable, bot blotty" [JH 1833].
Lord Oxmantown [Rosse] informs me that in the observations of this nebula at Birr Castle there is no mention of resolvability; and that "the central part to the right of star Alpha consists of bunches or patches of bright nebulosity, with fainter nebulosity intervening."
The spectrum of this nebula indicates that it possesses a gaseous constitution. One bright line only was seen, occupying in the spectrum apparently the same position as the brightest lines of nitrogen. When the slit was made as narrow as the intensity of the light would permit, this bright line was not so well defined as the corresponding line in some of the other nebulae under similar ocnditions of the slit, but remains nebulous at the edges.
When the brightest position of the nebula containing the nucleus or "bright knot" was brought upon the slit, in addition to the bright line a faint narrow continuous spectrum was seen.
The bright knot appeared in my telescope smaller and more condensed than it is represented in the drawings of Sir John Herschel.

---

(*) "Mr. Mason declares the upper and larger knot to be irresolvable by his telescope (a reflector of 12 inches aperture and 14 feet focal length). In this particular my observations of 1835 and 1837 so far agree, that its resolvability is not mentioned in words or indicated in the diagrams made on those observations." - Sir John Herschel, `Results of Astronomical Observations at the Cape of Good Hope,' p. 7 and pl. 2, fig. 1.

Lassell

[Memoirs of the Royal Astronomical Society, Vol. XXXVI (36)]
[Drawing on Plate II, Fig. 33]

Dreyer (1877)

GC 4403, h 2008 [M 17] (Omega Nebula). Drawing in Lassell, Plate II, Fig. 33.
Two drawings of this Nebula, by Trouvolot and Holden, are found in Professor Holden's interesting Paper on supposed Changes in the Nebula M. 17 (American Journal of Science and Arts, vol. XI., May 1876). Compare Wash. Obs., 1874, Plate VI.

Dreyer: NGC 6618.

NGC 6618 = GC 4403 = h 2008; M 17.
RA 18h 12m 42s, NPD 106d 13.9' (1860.0) [Right Ascension and North Polar Distance]
!!!, B, eL, eiF, 2 hooked; = M17
Magnificient, bright, extremely large, of extremely irregular shape, hooked like a "2" [number/digit "2"].
Remark: Figures in P.T. 33 [JH 1833], plate XII, fig. 35; C.G.H. [JH 1847], plate II, fig. 1; Lam. [Lamont, Ueber die Nebelflecken, Munich, 1837], plate I, fig 10; Mason [Mason and Smith, Transactions of American Philosophical Society, vol. vii], plate VI, fig. 1; Lass 2 [Lassell, Memoirs R.A.S. vol. xxxvi], plate VII, fig. 33; Wash [Holden and Trouvelot, Washington Observations, 1874, App. I], plate VI, fig. 3; Holden, Trouvelot [Amer. Journ. 1876], p. 348; Le Saeur [Proc. R.S. xviii], plate I; Ld R [Observations of Nebulae and Star Clusters at Birr Castle, 1848-78 (Transactions Royal Dublin Society, vol. ii. 1880)], plate VI.

Curtis

[Descriptions of 762 Nebulae ans Clusters photographed with the Crossley Reflector. Publ. Lick Obs., No. 13, Part I, p. 9-42]
NGC 6618, RA=18:15.0, Dec=-16:13. [Publ. Lick Obs.] Vol. VIII, Plate 58. M. 17; the ``Horse Shoe'' or ``Omega'' Nebula. Very bright, very large nebulosity, showing a wealth of detail, filling an area about 26'x20'. 0 s.n.