M45: The Pleiades Star Cluster

Explanation: Perhaps the most famous star cluster on the sky , the Pleiades can be seen without binoculars from even the depths of a light-polluted city . Also known as the Seven Sisters and M45 , the Pleiades is one of the brightest and closest open clusters . The Pleiades contains over 3000 stars, is about 400 light years away , and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the brighter cluster stars . Low mass, faint, brown dwarfs have also been found in the Pleiades . ( Editors' note: The prominent diffraction spikes are caused by the telescope itself and may be either distracting or provide aesthetic enhancement, depending on your point of view.)