Al di la della Luna; Beyond the Moon; Astrophotography; Astrofotografia; Danilo Pivato
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The Analysis of Frame
M 75; NGC 6864; Gcl 116; C 2003-120; BD-22 5331; GCRV 12454; --- Globular Cluster in Sagittarius - [field: 0,45° x 0,67°] --- Mag. Limite: --.-^ - -.-^ - Fonte: SDSS   - Object Coordinates RAJ2000.0:  20h 06m 04.841s - Dec J2000.0: -21° 55' 20.14" [SIMBAD] - Magnitudine: 08.61^ (r); 08.26^ (v); --.--^ (b); --- Surface Brightness: --.-^ - Object Size:  6.8' x 6.8' - - Position Angle: --° - Object alassification: I ; Redshift: z(~):  -0.000631
Ammasso globulare non tanto esteso apparentemente (diametro 6,8' x 6,8') - si suppone sia gigantesco - individuabile in una zona della costellazione del Sagittario povera di stelle luminos -, 8° circa SO di b Capricorni, presso il confine orientale della costellazione del Sagittarius. E' tra gli ammassi globulari più compatti e concentrati che si conoscono ed anche tra i più distanti fra quelli catalogati da C. Messier. Fu scoperto da Pierre Méchain il 27 agosto 1780 e incluso nel catalogo di nebulose e ammassi stellari di Charles Messier lo stesso anno; quest'ultimo la descrisse come una "nebulosa senza stelle tra Sagittarius e la testa del Capricorno". Il primo a risolverlo in stelle fu William Herschel, assieme a numerosi altri ammassi globulari Distante 67500 anni luce attualmente (2021) si conoscono 38 stelle variabili RR Lyrae, 62 candidate Blue Stragglers. Dalle ultime ricerche M75 sembra aver fatto parte di Gaia Sausage, i resti ipotizzati di una galassia nana che si è fusa con la nostra Via Lattea (C., Myeong, G.; et al. (August 2018), "The Sausage Globular Clusters", The Astrophysical Journal Letters863)
History of Observation and description of the M75:

Discovered by Pierre Méchain on August 27, 1780.

Charles Messier: October 18, 1780. 75. 19h 53m 10s (298d 17' 24") -22d 32' 23"
Méchain: (298d 17' 30") -22d 32' 00"
"Nebula without star, between Sagittarius & the head of Capricorn; seen by M. Méchain on August 27 & 28, 1780. M. Messier looked for it on the following October 5, & on October 18, compared it [i.e., its position] with the star 4 Capricorni, of sixth magnitude, according to Flamsteed: it seemed to M. Messier to be composed of nothing but very small [faint] stars, containing nebulosity: M. Méchain reported it as a nebula without stars. M. Messier saw it on October 5; but the Moon being above the horizon, & it was not until the 18th of the same month that he was able to judge about its form & determine its position."

Frederick William Herschel: [PT 1814, p. 279; SP2 p. 538]
Connoiss. 75 [M 75 = NGC 6864] is "A globular cluster of stars, and is a miniature of the third [M 3]."

[PT 1818, p. 448-449; SP2 p. 600]
The 75th of the Connoissance. [M 75 = NGC 6864]
"1799, 7 feet finder. It is just but visible."
"1799, 7 feet telescope. There is not the least appearance of its consisting of stars, but it resembles other clusters of this kind, when they are seen with low space-penetrating and magnifying powers."
"1810, 10 feet telescope. With 71 it is small and cometic."
"1784, 1785, 20 feet Newtonian. Easily resolvable; some of the stars are visible."
"1810, 20 feet, front view. It is a globular cluster."
"1799, 1810, large 10 feet. Its diameter with 171 is 1' 48"; with 220 it is 2' 0"."
By the observation of the 20 feet Newtonian telescope, the profundity of this cluster must be of the 743d order.

John Frederick William Herschel: h 2064 = M75.
Sweep 369 (September 3, 1831)
RA 19h 56m 2.5s, NPD 112d 23' 31" (1830.0) [Right Ascension and North Polar Distance]
vB; R; vsvmbM; 2'; a bright R ball 15" diam, in an atmosphere 2'; 320 does not show the stars but makes it more resolvable.
very bright; round; very ssuddenly very much brighter toward the middle; 2' [diameter]; a bright round ball of 15" diameter, in an atmosphere of 2'; [magnification] 320 does not show the stars but makes it more resolvable [mottled].

Sweep 298 (September 22, 1830)
RA 19h 56m 2.7s, NPD 112d 23' 38" (1830.0) [Right Ascension and North Polar Distance]
pB; R; psvmbM; r; 90".
pretty bright; round; pretty ssuddenly very much brighter toward the middle; round; 90" [diameter].

Sweep 275 (July 28, 1830)
RA 19h 56m 2.9s, NPD 112d 24' 10" (1830.0) [Right Ascension and North Polar Distance]
Not B; S; R; psbM; 2' diam; r, but not resolved. An insignificant object.
Not bright; small; round; pretty suddenly brighter toward the middle; 2' diameter; mottled, but not resolved. An insignificant object.

William Henry Smyth: DCCXXX [730]. M75. DCCXXX. 75 M. Sagittarii.
AR 19h 56m 38s, Dec S 22d 22'.0
Mean Epoch of Observation: 1834.62 [Aug 1834]
A globular cluster in the space between the left arm of Sagittarius and the head of Capricorn, and 7deg 1/2 degrees to the south-south-west of Beta Capricorni. It is a lucid white mass among some glimpse stars, with a large [bright] one in the nf [north following, NE] verge field. It was discovered by Pierre Mechain in 1780, who considered it as a nebula without stars; but Messier viewed it as a mass of very small stars, which opinion, on an object which at best is rather faint, was bold. In 1784, it was resolved by William Herschel's 20-foot Newtonian, and, on being gauged, was assigned a profundity of the 734th order. No wonder that this miniature of 3 Messier [M3] (No. CCCCXCII [492]) should be pale to gaze.

John Herschel, General Catalogue: GC 4543 = h 2064 = M75.
RA 19h 57m 49.1s, NPD 112d 18' 47.5" (1860.0). [Right Ascension and North Polar Distance]
Glob. Cl.; B; pL; R; vmbMBN; rr. 10 observations by W. & J. Herschel.
Globular cluster; bright; pretty large; round; very much brighter to the middle where there is a bright nucleus; partially resolved/some stars seen.

John Louis Emil Dreyer: NGC 6864 = GC 4543 = h 2064; Méchain, M 75.
RA 19h 57m 49s, NPD 112d 19.0' (1860.0). [Right Ascension and North Polar Distance]
Glob. Cl., B, pL, R, vmbMBN, rr; = M75
Globular cluster, bright, pretty large, round, very much brighter to the middle where there is a bright nucleus, partially resolved/some stars seen.

Heber Doust Curtis: [Descriptions of 762 Nebulae and Clusters photographed with the Crossley Reflector. Publ. Lick Obs., No. 13, Part I, p. 9-42]
NGC 6864, RA=20: 0.2, Dec=-22:12. M. 75. Bright compact globular cluster 2' in diameter. Greatly condensed at center. 9 s.n.

Since: 01/01/2004
Since: 01/11/2010