Messier 50

Probably discovered by G.D. Cassini 1711.
Discovered independently by Charles Messier on April 5, 1772.

Messier: M50.

April 5, 1772. 50. 6h 51m 50s (102d 57' 28") -7d 57' 42"
"Cluster of small stars, more or less brilliant, above the right loins of the Unicorn, above the star Theta of the ear of Canis Major, & near a star of 7th magnitude. It was while observing the Comet of 1772 that M. Messier observed this cluster. He has reported it on the chart of that comet, on which its trace has been drawn. Mem. Acad. 1772."

[Objects discovered by others, not found by Messier: Cassini; appendix to Messier Catalog of 1780 and 1781]
M. de Cassini [Jacques Cassini, Cassini II] reported in his Elements of Astronomy, p. 79, that his father [G.D. Cassini] discovered a nebula in the area between Canis Major and Canis Minor and which was one of the finest to be seen in the telescope.
M. Messier looked several times for this nebula in a serene sky, without being able to find it, and he presumes it might have been a comet just becoming visible or disappearing, for nothing resembles a nebula more than a comet which is just becoming visible in an instrument.
[Actually, this was probably M50. See below.]

[Mem. Acad., 1777, p. 345-359, on the comet of 1772 (Messier's 13th, discovered by Montaigne, actually comet 3D/Biela); here p. 349]
[April 5, 1772] I determined, in the same evening, the position of a cluster of small starsplaced between the star Theta in the earof Canis Major, & the right loins of Monoceros; I compared this cluster with the telescopic star, determined on April 3, & this one with a star of the seventh magnitude which was near the cluster. The positions are reported in the second table.
[p. 351] RA: 102.57.28, Dec: 7.57.41.A. Star cluster.
[The position of M50 is given in the chart on Pl. VI, facing p. 352]

Cassini

[Jacques Cassini, 1740. Élémens d'astronomie. Here p. 79. 1740elas.book.....C]
One can assemble the number of these [nebulous] stars, which is in Cancer, in the Head of Sagittarius, & one other which my father [G.D. Cassini] has discovered in the space which is between Canis Major & Canis Minor, which is one of the most beautiful which one can see with the [refractor] telescope.

Bode: Bode 16.

"A star cluster on a nebula."
"On December 2 [1774], I wanted to look up the nebulous star which Mr. Cassini is said to have seen between the Large and the Small Dog [CMi and CMa], and of which I could nowhere find a closer description of its position. Eventually I found in this area, north of the stars Theta, Mu and Gamma at the head of CMa, or below the belly of Mon, a small cluster on a nebulous ground, with which 4 small stars to the west form the shape shown in the 9th figure. Its separation from the star Theta is 4deg 10' and from Gamma 7deg 29', after my measurements. I suppose that this may perhaps be the Cassinian nebulous star."

William Herschel

[Unpublished Observations of Messier's Nebulae and Clusters. Scientific Papers, Vol. 2, p. 657]
1785, March 4 (Sw. 377). A very brilliant cluster of large [bright] stars, considerably compressed and rich, above 20' in diameter, the stars of various sizes [magnitudes], visible in the finder.

John Herschel (1833): h 425.

h 425 = M50.
Sweep 16 (February 13, 1826)
RA 6h 54m 42.2s, NPD 98d 5' 19":: (1830.0) [Right Ascension and North Polar Distance]
Rich; comp; fills field; stars 10...15m; place of a * 10m in middle - a fine cluster.
Rich; compressed; fills field; stars of 10th to 15th magnitude; place [given is that] of a star of 10th magnitude in the middle [of the cluster] - a fine cluster.

Sweep 135 (March 13, 1828)
RA 6h 54m 45.5s, NPD 98d 6' 55" (1830.0)
A L rather straggling cl 10..12' diam; st 11....15 m. The largest in M, taken.
A large rather straggling cluster, 10 to 12' diameter; stars of 11th to 15th magnitude. The largest in the middle, taken [for position measurement].

Sweep 318 (January 8, 1831)
RA 6h 54m 46.6s, NPD 98d 6' 58" (1830.0)
Superb cl; fills whole field; irreg R; stars 11...15 m; not comp in M; straggling stars extend over a circle 30' in diameter.
Superb cluster; fills whole field; irregularly round; stars of 11th to 15th magnitude; not compressed in the middle; straggling stars extend over a circle 30' in diameter.

Sweep 136 (March 14, 1828)
RA 6h 54m 49.4s, NPD 98d 6' 2" (1830.0)
A fine v L sc cl; has a red star 8.9 m to s of the more compressed part.
A fine very large scattered cluster; has a red star of 8 or 9 mag to south of the more compressed part.

Smyth: CCLXXIV [274]. M50.

CCLXXIV. 50 M. Monocerotis.
AR 6h 55m 11s, Dec S 8d 06'.7
Mean Epoch of Observation: 1833.25 [April 1833]
Position 170d.0 (w 1), Distance 5".0 (w 1)
A delicate and close double star in a cluster of the Via Lactea [Milky Way], on the Unicorn's right shoulder. A [mag] 8 and B 13, both pale white. This is an irregularly round and very rich mass, occupying with its numerous outliers more than the field, and composed of stars from the 8th to the 16th magnitudes; and there are certain spots of splendour which indicate minute masses beyond the power of my telescope. The most decidedpoints are, a red star towards the southern verge, and a pretty little equilateral triangle of 10th sizers, just below, or north of it. The double star here noted was carefully estimated under a full knowledge of the vertical and parallel lines of the field of view: this was made triple by H. [John Herschel], whose 2357 of the Fifth Series it is; but he must be mistaken in calling it Struve 748, which is Theta Orionis. It is sufficiently conspicuous as a double star, and though I perceive an infinitesimal point exactly om the vertical of A, I cannot ascertain whether it is H.'s C.
This superb object was discovered by Messier in 1771 [actually 1772], and registered "a mass of small stars more or less brilliant." It is 9deg north-north-east of Sirius, and rather more than one-third of the distance between that star and Procyon.

John Herschel, General Catalogue: GC 1483.

GC 1483 = h 425 = M50.
RA 6h 56m 12.5s, NPD 98d 8' 46.5" (1860.0). [Right Ascension and North Polar Distance]
! Cl; vL; Ri; pC; E; st 12...16 8 observations by W. & J. Herschel.
Remarkable cluster; very large; rich; pretty compressed; extended; stars from 12th to 16th magnitude.

Dreyer: NGC 2323.

NGC 2323 = GC 1483 = h 425; M 50.
RA 6h 56m 13s, NPD 98d 8.8' (1860.0). [Right Ascension and North Polar Distance]
! Cl, vL, Ri, pC, E, st 12...16; = M50
Remarkable cluster, very large, rich, pretty compressed, extended, stars from 12th to 16th magnitude.