Messier 39

Perhaps noted by Aristotle about 325 BC.
Perhaps seen by Le Gentil in 1750.
Discovered by Charles Messier on October 24, 1764.

Messier: M39.

October 24, 1764. 39. 21h 23m 49s (320d 57' 10") +47d 25' 00"
Cluster of stars near the tail of the Swan; one can see them with an ordinary telescope of 3.5 feet [FL]. (diam. 1d 00')

[Mem. Acad. for 1771, p. 450 (first Messier catalog)]
In the night of October 24 to 25, 1764, I observed a cluster of stars near the tail of Cygnus: One distinguishes them with an ordinary (nonachromatic) refractor of 3 and a half feet [FL]; they don't contain any nebulosity; its extension can occupy a degree of arc. I have compared it with the star Alpha Cygni, & I have found its position in right ascension of 320d 57' 10", & its declination of 47d 25' 0" north.
[p. 458] 1764.Oct.24. RA: 320.57.10, Dec: 47.25. 0.B, Diam: 1. 0. Cluster of stars near the tail of Cygnus: it doesn't contain any nebulosity.

Bode: Bode 75.

A star cluster.
On October 27 [1774], I found in a triangle west and east with the two stars Pi at the tail of Cygnus a small star cluster, the position of which relative to the given stars I determined with the heliometer, as shown in the 6th figure.

William Herschel:

[Unpublished Observations of Messier's Nebulae and Clusters. Scientific Papers, Vol. 2, p. 654]
1788, Sept. 27 (Sw. 866). Consists of such large and straggling stars that I could not tell where it began nor where it ended. It cannot be called a cluster.

John Herschel (1833): h 2126.

h 2126 = M39.
Sweep 209 (September 14, 1829)
RA 21h 26m 7.8s, NPD 42d 18' 52" (1830.0) [Right Ascension and North Polar Distance]
A * 7m, one of a large loose cluster of stars 7 .... 10m; very coarsely scattered, and filling many fields.
A star of 7th mag [position taken], one of a large loose cluster of stars of 7th to 10th magnitude; very coarsely scattered, and filling many fields [of view of JH's telescope].

Smyth: DCCLXXXVIII [788]. M39.

DCCLXXXVIII. 39 M. Cygni.
AR 21h 26m 29s, Dec N 47d 43'.8
Mean Epoch of Observation: 1836.72 [Sep 1836]
A loose cluster, or rather splashy galaxy field of stars, in a very rich visinity between the Swan's tail and the Lizard, due south of Beta Cephei, and east-north-east of Deneb [Alpha Cygni]. This was picked up by Messier in 1764, with his 3 1/2 foot telescope, and registered as being a degree in diameter. Among them there are several pairs, of which a couple were slightly estimated; the first being the brightest star (7m) and its comes, and the second a pretty pair of 10th-magnitudes:

    First pair.  Pos. 26d 0' (w l)  Dist 85".0 (w l)  } Ep. 1836.72
    Second pair.      12d 0' (w l)        8".0 (w l)  }
  

John Herschel, General Catalogue: GC 4681.

GC 4681 = h 2126 = M39.
RA 21h 27m 12.6s, NPD 42d 10' 58.0" (1860.0) [Right Ascension and North Polar Distance]
Cl; vL; vP; vlC; st 7...10 3 observations by W. & J. Herschel.
Cluster; very large; very poor; very little compressed; stars between 7th and 10th magnitude.

Dreyer: NGC 7092.

NGC 7092 = GC 4681 = h 2126; M 39.
RA 21h 27m 13s, NPD 42d 11.0' (1860.0) [Right Ascension and North Polar Distance]
Cl, vL, vP, vlC, st 7...10; = M39
Cluster, very large, very poor, very little compressed, stars between 7th and 10th magnitude.