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Object description
NGC 6522 and NGC 6528 - 2 Globular Clusters in the Constellation Sagittarius

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.

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.

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