Galaxies

16 03 2009

On a typical night, looking into the sky, you can see somewhere between 500 and 6000 stars, depending on how dark your night sky is. If you live in a reasonably dark area, you may be lucky enough to see a faint, diffuse band stretching across the sky, from horizon to horizon. This band, known as the Milky Way, is the plane of our home galaxy.

It was Galileo who discovered that this band consisted of an almost uncountable number of stars, after he turned his telescope to the sky. Prior to this, it was believed that the Milky Way was a ‘cloud’ that spanned the entire sky.

360-degree photographic panorama of the Milky Way. (Digital Sky LLC)

360-degree photographic panorama of the Milky Way. (Digital Sky LLC)

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Clusters

20 01 2009

Star clusters are groups of stars that are gravitationally bound. Two distinct types of star cluster can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars, while open clusters generally contain less than a few hundred members, and are often very young. Open clusters become disrupted over time by the gravitational influence of giant molecular clouds as they move through the galaxy, but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound; they are then known as a stellar association, sometimes also referred to as a moving group. Read the rest of this entry »