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NGC 6522 and NGC 6528 - 2 Globular Clusters in the
Constellation Sagittarius |
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Object description:
The two globular clusters NGC 6522 (right) and NGC
6528 (left) in the constellation Sagittarius are both about 25 000
light years away from Earth. NGC 6522 is assigned to concentration
class VI, NGC 6528 to class V, according to Shapley-Sawyer.
NGC 6528 appears slightly more yellow than NGC 6522 due to the slightly higher
interstellar absorption of the blue light components. Directly below NGC 6528
lies the dark cloud Barnard 298.
Both globular clusters lie near the
center of our Milky Way, in a small region of the sky called Baade's Window.
Walter Baade discovered in 1951 a region only about 1/4 square degree (apparent
full moon size), nearly free of interstellar gas and dust absorption, which -
viewed from Earth - allows a direct and unobstructed view of the stars of the
galactic center (bulge) about 30 000 light years away and their
investigation. |
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The
central coordinates of Baade's window are RA: 18 h 03 m 32.14 s and DE: -30 d
02 m 06.96 s. Outside this region observation is not possible due to absorption
by dust clouds.
Both star clusters were discovered by Friedrich Wilhelm
Herschel on June 24, 1784. A
scientific
publication from 2008 suggests that NGC 6522 might be the oldest (> 12
billion years) globular cluster in our Milky Way.
The bright star at the
bottom of the image is gamma Sagittarii (Alnasl), one of the main stars of the
constellation Sagittarius.
« Click here or the thumbnail to load a large annoted image
and a size comparison to the full moon. |
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All Images and all Content are ©
by Franz Hofmann + Wolfgang Paech |