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The open cluster NGC 6520 and Barnard 86 in the
constellation Sagittarius |
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Short Object description:
Our image shows the bright open star cluster NGC 6520
and its strange neighbor Barnard 86, a dark cloud that reminds us of the
silhouette of a gecko. The cosmic couple stands against the background of
millions of stars in the brightest part of our Milky Way. The stars of the
Milky Way in this region of the sky are so densely crowded that there is hardly
any dark sky left between them.
This part of the constellation
Sagittarius is home to one of the most densely populated star fields in the
entire sky - the great Sagittarius star cloud. The multitude of bright stars
create a dramatic contrast to black dark clouds like Barnard 86 in the center
of this image, taken with our 12.5 inch Planewave Astrograph. |
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Barnard
86, a so-called Bok globule, was described by his discoverer Edward Emerson
Barnard as a "drop of ink on a bright star background". Barnard was an American
astronomer who, among numerous other contributions to science, discovered and
photographed a large number of comets, dark clouds and a Jupiter moon. As an
exceptionally gifted visual observer and astrophotographer, Barnard was the
first to make long time exposures to study dark clouds. Barnard included the
object in his
catalogue of dark nebulae in 1905.
Barnard 86 lies
in front of the star field when viewed from Earth. The small grains of dust
that make up the cold and dense dark cloud absorb the light of the stars behind
it and it appears opaque. Presumably we can see here the remains of the
molecular cloud which collapsed to form the nearby star cluster NGC 6520. The
few stars that seem to stand in the middle of Barnard 86 are in reality in the
foreground, between us and the dark cloud.
As a young open cluster of
stars, NGC 6520 contains many hot stars. Its blue-white glow reveals its
low age. Usually open star clusters consist of several thousand stars that have
formed at the same time and are therefore of the same age. They usually stay
together for only a comparatively short time - a few hundred million years -
before slowly drifting apart. The age of the stars in NGC 6520 is estimated to
be "only" 150 million years. Together with Barnard 86, the star cluster stands
at a distance of almost 2000 light years from our solar system. NGC 6520 was
discovered on 24 May 1784 by Friedrich Wilhelm Herschel.
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Click here or the thumbnail image for a comparison with the
size of the Moon. |
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