AAO image reference AAT 93a. « Previous || Next »
Top left is NE. Image width is about 50 arc min
Image and text © 2000-2010, Australian Astronomical Observatory, photograph by David Malin.
Around the inner part of the Milky Way swirl vast numbers of relatively faint, old, yellow stars. They are seen overhead on southern winter nights as the brightest part of the Milky Way, the star clouds of Sagittarius. The Galactic centre is itself obscured by dust clouds at visible wavelengths, but in the late 1940s, Walter Baade, working at Mt Wilson Observatory in California, identified a relatively clear region with a line of sight that passed within 4 degrees of Galactic centre. In this direction the obscuration is fairly small and uniform, which accounts for the uniformity of the star field.
It was in this direction, in a 'window' of about 30 arc minutes across around the globular cluster NGC 6522 (centre), that he was able to determine the first reliable distance to the centre of the Galaxy. Modern measurements place it at about 25,000 light years away, slightly greater than Baade's result, which was published in 1951. The fainter globular cluster at the eastern (left) edge of Baade's Window is NGC 6528.
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