The Caldwell Objects

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Barnard's Galaxy
NGC 6822
Type: Irregular Barred
Dwarf Galaxy (IBm)
Con: Sagittarius
RA: 19 h 44.9 m
Dec: -14° 48'
Mag: 8.8; 7.9
(O'Meara)
Diam: 15.0'
SB: 14.8
Dist: 2.3 million light-years
Disc: Edward Emerson
Barnard, 1884
HERSCHEL: None.
GC: None.
NGC (original): Very faint, large, extended, diffused
NGC 6822 IN SAGITTARIUS IS ARGUABLY the
most celebrated and important deep-sky
discovery made by Edward Emerson Barnard —
one of history's greatest visual astronomers.
Barnard swept up this large and elusive glow in
1884 with the 5-inch Byrne refractor at Van -
derbilt University Observatory. At the time
Barnard had no idea of the nebula's extra-galactic
nature. Sadly, he would pass away in 1923 — just
one year before Edwin Hubble would use the
famous 100-inch reflector atop Mount Wilson to
identify several Cepheid variables in it. When
Hubble worked out the distances to these stars,
he realized that NGC 6822, like the Andromeda
"Nebula," is not part of our Milky Way but a selfcontained
stellar system far beyond. Barnard's
Galaxy (as NGC 6822 would soon become
known) had emerged from the stellar foreground
of the Milky Way to stand out boldly as an
independent galaxy — a small
The Caldwell Objects
NGC 2000.0: Very faint, very small, extended, diffused; the
same as IC 4895.
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but important member of our Local Group.
The photographs Hubble took with the 100-inch
resolved NGC 6822 to its core, allowing him to
identify numerous variable stars, clusters, and
nebulae. Ironically, Hubble's visual impression of
the object through the same telescope was much
different. Hubble wrote that NGC 6822 was
"fairly conspicuous" at low power in a 4-inch
finderscope but "barely discernible at the primary
focus of the 100-inch." So a bigger aperture isn't
necessarily always better. Indeed, observations of
the object made with other large telescopes led to
some confusion. For instance, compare the NGC
2000.0 description with the original NGC description
tabulated above. In the former the 15' x
15' galaxy is described as being "very small," not
"large" as in the latter; it is also identified as IC
4895 there. In a 1925 Astrophysical Journal article,
Hubble describes why:
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