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RA: 19h 53m 46.11s
Dec: +18° 46′ 42.3″
Ch: MSA:1219, U2:162, SA:8
Ref: SIMBAD, Collinder (1931), SEDS
Type: globular cluster
Mag: B=7.91, V=6.1
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NGC 6838 = M 71 may also be NGC 6839, which see -- but probably not.
In the Philosophical Transactions, 1818, William Herschel wrote: "1794, 7 feet telescope. With 120 and 160 power the stars of it become just visible. 1783, 1799, 1807, 20 feet telescope. A cluster of stars of an irregular figure. 1784, 1799, 1807, 20 feet telescope. It is situated in the milky way, and the stars are probably in the extent of it; it is however considerably condensed; about 3' diameter. 1805, large 10 feet telescope. An irregular cluster of very small stars, 2' 35 seconds in diameter."
Doig, P. (1925) Notes on the nebulae and clusters in Webb's 'Celestial Objects for Common Telescopes' (Sixth edition, Vol.ii). Part IV. M.N.R.A.S., 36(2), 58.
Charlier, C V L (1931) "Stellar clusters and related celestial phaenomena", Lund Annals 2, 14, No. 19. Charlier examined prints from the Franklink-Adams atlas, and notes: ". . . by J Herschel described as a mass of closely packed stars, irregular or triangular . . . On the FAC the triangular form observed by J H well visible, but perhaps due to foreign stars projected on the cluster." He notes that although Melotte calls it a globular, the NGC calls it an ordinary cluster, and it is not named in Bailey's catalogue of globular cluster published in H.A. 76.
This is a rich star cluster of the rare intermediate type between open clusters and globulars. In a very small instrument it is a 9th magnitude glow some 7' across. A larger telescope, or perhaps just a higher power, resolves it into a swarm of tiny stars. Burnham notes that this cluster "was probably first observed by Koehler at Dresden about the year 1775, but may have been noted by de Cheseaux as early as 1746. In June 1780 it was rediscovered by Mechain, which prompted Messier to search for it later that year; he found it "very faint... it contains no star... The least light extinguishes it... diam 3.5'... it was reported on the chart of the comet of 1779..." The NGC describes is as a very large and very rich cluster, which is pretty much compressed, consisting of stars of 11..16 magnitude. Webb wrote of it as "large and dim, hazy to low power with 3.7 inch; yielding to a cloud of faint stars to higher powers... Interesting specimen of the process of nebular resolution. About 1 S.p. M71 is a beautiful low-power field containing pair and triple group, all about 8 or 9 mag..." This last comment most probably refers to the well spread out open cluster Harvard 20, also called Collinder 408. Isaac Roberts, pioneering 19th century astrophotographer who discovered the spiral nature of M31, used a 20-inch reflector to photograph the cluster in the 1890's. He decided that M71 was a spiral: ".. the surrounding region densely crowded with stars down to about mag 17... arranged in remarkable curves and lines which are very suggestive of having been produced by the effects of spiral movements." Burnham states that six red M-type giants are known in the cluster, one of which is the irregular variable Z Sagittae. Four of the six lie near the eastern edge of the cluster, the remaining two towards the south.
A study by W. W. Morgan of Yerkes Observatory indicates this globular cluster to have a spectral type of G2.
RA 19 53 46.1 (2000) Dec +18 46 42 Integrated V magnitude 8.19 Central surface brightness, V magnitudes per square arcsecond 19.22 Integrated spectral type G1 Central concentration, c = log(r_total/r_core); a 'c' denotes a core-collapsed cluster 1.15 Core radius in arcmin .63. ["Catalog Of Parameters For Milky Way Globular Clusters", compiled by William E. Harris, McMaster University. (Revised: May 15, 1997; from http://www.physics.mcmaster.ca/Globular.html; Harris, W.E. 1996, AJ, 112, 1487) ]
The RNGC (Sulentic and Tifft 1973) notes that this is a 8.5 mag globular cluster.
A catalogue of star clusters shown on Franklin-Adams chart plates. Mem.R.A.S., 60(5), 175-186.
Houston notes that "on a good night an 8-inch telescope can resolve stars right to its centre."
John Bortle (Webb Society Quarterly Journal, January 1976) using 10x50 binoculars, estimates the visual magnitude as 8.0.
AJ Crayon, using an 8" f/6 Newtonian, notes: "(M 71) is a globular cluster. It is faint and stellar in an 8X50 finder. In the 8" it is 15' 9m, 12 stars resolved against haze of unresolved stars, most of resolved ones in eastern half with a trail to the west, at 115X."
Steve Coe, observing with a 13" f/5.6, notes: "(M 71) This compact star cluster has been called an open and a globular. It is bright, pretty large, very rich and much compressed at 135X. At 165X on a good night, I can see an arrowhead shape to the cluster and count 56 stars across the mottled face of this cluster. The cluster is easy to pick out of the Milky Way with the 11 X 80 finder. I have observed this object in several large scopes and it is always difficult to determine where the cluster stops and the backround stars begin. In the Lines' 20" f/6 at 150X and in the Lowell Observatory 24" Clark refractor at 380X this very compact cluster was fascinating. There are many curving lines of stars with dark lanes between them. Camp 613 13" 7/10-- seen in 11X80, 100X--bright, pretty large, rich, very much compressed, somewhat brighter middle, 21 stars resolved of mags 11..., located in a rich field of view. 330X--53 stars counted, arrowhead shape points east, several close double stars involved, averted vision reallys fills in stars. All the stars are white, with several nice pairs, about half the stars counted are seen with averted vision only."
Observer: Steve Coe; Your skills: Advanced (many years); Date/time of observation: 22 June 98; Location of site: Strawberry, Arizona USA (Lat +34, Elev 7000 ft); Site classification: Rural; Sky darkness: 9 1-10 Scale (10 best); Seeing: 8 1-10 Seeing Scale (10 best); Moon presence: None - moon not in sky; Instrument: 13" f/5.6 Newt on Bigfoot German EQ mount; Magnification: 100X, 220X, 440X; Filter(s): none; Object(s): M 71;
Description: The bright globular is seen in the 11X80 finder: it is easy in a rich Milky Way field of view. At 100X in the 13" it is bright, large, much compressed, rich and has 14 stars resolved in a triangular shape. Moving up to 220X resolves 28 stars across a silvery surface of unresolved stars, the 12th mag star in the center is a double of equal magnitude. At 440X there are 57 stars seen and the double in the middle is split nicely. At this high power on a superb night in the Arizona mountains, it seems that this is all that the 13" will show on this object, a lovely compressed ball of stars afloat in a rich Milky Way field of view. --
Tom Lorenzin, in the e-version of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing", notes: "9M; 6' diameter; oddly shaped; not round! many 12M and dimmer stars resolved against glow of diffuse background; sparse and dim cluster H-20 (9.6M; 8' diameter) 30' SSW."
Donald J. Ware:"This globular cluster is about 6' in diameter, and show many stars resolved across its face. The shape is intriguing, as it is arrowhead or chevron shaped, pointing to the west. Binoculars show a faint unresolved patch of light in an interesting field."
Alldays (22.50S, 20.12E, 770m).
12-inch f/10 SCT (95x, 218x)
Faint stars overlaid this globular which had the looks of a cluster, soft haze brighter to the middle. The N-NE is much busier, with faint string of stars running out into the field of view. Slightly elongated in a E-W direction. Dark patches can be seen with care. Lovely double star on the western edge of the cluster. A handful of brighter stars can be seen just to the west in the field of view. More or less 50 same magnitude stars.
16-inch f/10 SCT (127x, 290x)
Very much the looks of a cluster, very different in the cluster class. Elongated in a N-S direction and faint stars show a sort of 'S' on this globular misty surface. The south end seems slightly more busy in faint starlight.
Instrument:12"Dobsonian Reflector Telescope.
Sky Conditions:Dark moon and stars magnitude 6 and fainter are barely visible with the naked eye.
Transparency of the Sky:The most clear sky possible.
Seeing:Excellent clean sky,limited star flickering and brilliant objects.
First Impression:Globular Cluster.
Chart Number:No.12(Extract taken out of "Atlas of the Night Sky").
Size:26mm Eyepiece:Field of View:57'/9=6.3'.
20mm Eyepiece:Field of View:50'/8=6.2'.
Size in Arc Minutes:6.2'.
Size of nucleus vs.halo:9/6.2'=1.4'.
Size of halo:1.3'.
Globular Cluster is 6.2'*1.5'.
Brightness Profile:Medium Surface Brightness.
Challenge Rating:Fairly easy to observe this globular cluster in a very dark sky.
By making a careful observation of this globular cluster the stars are partially resolved.All the stars in this globular cluster are spherically concentrated towards each other.This globular cluster looks like an irregular snowball in appearance of bright stars.In this globular cluster I have found some chain of stars.I have also noted some starless patches around the outskirts of this globular cluster.
The Messier objects
The Bennett objects
The Caldwell list
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