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| The German-American astronomer Walter Baade selected for study a region of the crowded star fields in Sagittarius where he believed the Galactic dust obscuration was both uniform and minimal. He used this line of sight to establish the distance of the unseen Galactic centre, using variable stars as his yardstick. He found it to be about 30 000 light years away. This part of the sky, around the globular cluster NGC 6522, is now known as Baade's window. The brightest star in the photograph is gamma Sagittarii, a deep yellow, naked eye star of about third magnitude. It is in the foreground at a distance of about 100 light years. |