Celestial hemisphere:  Southern  ·  Constellation: Sagittarius (Sgr)  ·  Contains:  Barnard's Galaxy  ·  NGC 6822
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NGC 6822 - Barnard Galaxy - three nights - 11 hours of subs :-), Daniel Nobre
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NGC 6822 - Barnard Galaxy - three nights - 11 hours of subs :-)

Getting plate-solving status, please wait...
NGC 6822 - Barnard Galaxy - three nights - 11 hours of subs :-), Daniel Nobre
Powered byPixInsight

NGC 6822 - Barnard Galaxy - three nights - 11 hours of subs :-)

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Well, its one of my images that I never could it would be possible from my own place - its the faint Barnard Galaxy, 1.6 Million LY away, that I think its a very curious galaxy...

July 21th, 22th and 24th...

hope you enjoy! :-)

...here is some history from Rich Jakiel - https://www.astronomy-mall.com/Adventures.In.Deep.Space/barnard.htm

Barnard's Galaxy or NGC 6822 is a small irregular galaxy only 14 degrees east of the galactic plane in the constellation of Sagittarius. A member of the Local Group of Galaxies, it is quite similar to the Small Magellanic Cloud in composition and structure. Though it has a fairly low surface brightness, NGC 6822 is one of the easiest galaxies to resolve. Numerous H II regions and bright supergiant stars can be resolved with only a 20cm telescope equipped with a CCD camera. Several large H II regions and the brightest stars are visible in large aperture telescopes under dark skies.

Today the galaxy is under intense scrutiny and has been the subject of numerous papers over the last thirty years. However the past observational history has been much more colorful. The low surface brightness of the galaxy itself combined with the relatively bright H II regions has lead to a great deal of confusion over its identity during the late 19th to early 20th centuries. The unique observational history of Barnard's Galaxy will be covered in much more detail in the next section of the paper.

Historical Observations

1) Early Work

The early observations of NGC 6822 are quite interesting and rather confused, representative of conditions under which the object was observed. NGC 6822 is a large, low surface brightness object and is best viewed at low magnification for maximum contrast of field. Barnard's early observations certainly reflect the challenging nature of this object. Barnard first observed the galaxy on August 17, 1884 with a 5-inch refractor. He described the object as.. "an excessively faint nebula" and "it is some 2' in diameter, and is very diffuse and even in its light" (Barnard, 1884). He later determined its position with a 6-inch equatorial and noted it was "seen with difficulty", while in the 5-inch at 30x it was "quite distinct". In 1885, he examined it again with a 6-inch refractor and a "comet" eyepiece. The wide field boosted the visibility of the galaxy, and Barnard made a most unusual observation (Hubble, 1925):

It certainly seems much larger and much denser than last year and I certainly think it has increased in density and size since that time...If it had always been as large and bright as now, I cannot conceive how it could have been missed by observers when examining G.C. 4510 (the bright planetary nebula NGC 6818, which is about 40' north preceding). Probably this is a variable nebula.

The problems associated with observing NGC 6822 will plague many observers over the next 40 years. Hubble in 1925 writes: NGC 6822 is fairly conspicuous in a short 4-inch finder...but is barely discernible at the primary focus of the 100-inch (Hubble, 1925; Burnham, 1977). Large refractors with their restrictive field of view were particularly ill-suited for the study of this low contrast object. The 26-inch at Leander McCormick Observatory completely missed the galaxy, instead the two brightest H II regions located on the north end of the galaxy were observed. The brighter of the two diffuse nebulae was assumed to be NGC 6822, while the fainter received the designation of IC 1308 (Hubble, 1925).

Even photography did not quickly resolve the discrepancies between Barnard's original observations and those made with much larger telescopes. Max Wolf at the Heidelberg Observatory photographed the region in 1906 and 1907. Wolf, using the 16-inch Bruce Camera and the 28.5-inch Walz Reflector identified the two largest diffuse nebulae as NGC 6822 and IC 1308. Wolf also noted a dense region of small clusters and nebulae (Wolf, 1907; Hubble, 1925). The "new" object was actually the main bar of the galaxy, now well resolved into stars and nebulae. It received the designation of IC 4895, and once again Barnard's original observations were overlooked. It took 15 years before Perrine (1922) of the Cordoba Observatory, Argentina, finally resolved the discrepancies in identification and interpretation. Perrine correctly identified that the diffuse nebulae and Wolf's group of small clusters were all part of the same system. He was the first to recognize its true nature as an extragalactic system. Perrine properly classified NGC 6822 as a Magellenic Cloud-type object. This helped cleared the way for Edwin Hubble's groundbreaking work in 1925.

2) Hubble's 1925 Paper

Edwin Hubble's 1925 paper: N.G.C. 6822, A Remote Stellar System remains as one of the great classical studies of the early 20th century. The galaxy's resemblance to the Magellenic Clouds led to intensive study by the large reflectors of the time. He conducted a detailed survey of the structure and stellar population of this system. Hubble discovered 15 variable stars (11 Cepheids), measured the distribution of stars down to magnitude 19.4, and described five "diffuse nebulae" (giant H II regions) plus determine the absolute magnitude of the entire system.

Hubble's discovery of eleven Cepheid variables was one of the most important milestones in galactic astronomy. Using the Cepheid Period-Luminosity relationship, Barnard's Galaxy became the first system beyond the Magellenic Clouds to have its distance determined (Hubble will soon follow suit with M31 and M33). He derived a distance of 214,000 parsecs, or over 700,000 light years, far beyond Harlow Shapley's 300,000 light years as the size of known universe. In one paper, Hubble resolved the "Great Debate" of 1920 between Curtis and Shapley over the scale of the universe and the nature of the "spiral nebulae". It soon became clear that all spiral nebulae were galaxies far beyond our own.

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NGC 6822 - Barnard Galaxy - three nights - 11 hours of subs :-), Daniel Nobre