M45 - The Pleiades, a.k.a. The Seven Sisters, is one of the closest open clusters to Planet Earth. This bright, blue bundle of stars can be seen with the naked eye on a clear night and has historically taken on various meanings by different cultures and traditions. The cluster is dominated by hot blue and extremely luminous stars that have formed within the last 100 million years. The brightest stars in this cluster are surrounded by molecular dust that was leftover from the formation of these giants. The Pleiades are a prominent sight in winter in the Northern Hemisphere and have been known since antiquity to cultures all around the world. Astronomers have generally found that the Pleiades are about 135 parsecs away from Earth. The cluster contains over 1,000 statistically confirmed members and is dominated by young, hot blue stars, up to 14 of which can be seen with the naked eye depending on local observing conditions. Ages for the Pleiades have been estimated between 75 and 150 million years and the cluster is slowly moving in the direction of the feet of what is currently the constellation of Orion. Astronomers estimate that the cluster will survive for about another 250 million years, after which it will disperse due to gravitational interactions with its galactic neighborhood. Under ideal observing conditions, some hint of nebulosity may be seen around the cluster, and this shows up in long-exposure photographs, like the attached photo I took last Sunday. It is a reflection nebula, caused by dust reflecting the blue light of the hot, young stars. Analyzing deep-infrared images obtained by the Spitzer Space Telescope and Gemini North telescope, astronomers discovered that one of the cluster's stars – HD 23514, which has a mass and luminosity a bit greater than that of the Sun, is surrounded by an extraordinary number of hot dust particles. This could be evidence for planet formation around HD 23514.