Globular clusters NGC 6522 and NGC 6528 in Sagittarius - Baade's Window around NGC 6522...

Globular clusters NGC 6522 and NGC 6528 in Sagittarius - Baade's Window around NGC 6522 - NGC 6522 (right) and NGC 6528 (left) are two clusters located about 25,000 years ago - light from Earth towards the center of our galaxy. Photo obtained with Siding Spring's 3.9m telescope. Around the nucleus 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 1940s, Walter Baade, working at Mt Wilson in the USA, identified a region with a line of sight close to the Galactic centre. This direction has the minimum of obscuration and it was here, in the 'window' around the globular cluster NGC 6522 (center of the image) 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