The Pleiades or M45 is an open star cluster 444 ly from Earth in the constellation of Taurus. It has been known since antiquity as it's one of the closest and most obvious cluster to the naked eye in the night sky. The cluster is dominated by blue middle-aged, hot B-type stars that are extremely luminous and have formed within the last 100 million years.
The dust that forms a faint reflection nebulosity around the brightest stars are not remnants from the formation of cluster, which would have dispersed by radiation pressure. Instead it's now know to be an unrelated dust cloud in the interstellar medium, through which the stars are currently passing.
The cluster contains over 1,000 statistically confirmed members, it's core radius is about 8 light years and the tidal radius is about 43 ly. The total mass contained in the cluster is estimated to be circa 800 solar masses. The cluster also contains many brown dwarfs, which are not heavy enough for nuclear fusion reactions to start in their cores and become proper stars.
The name of the Pleiades comes from Ancient Greek. It probably derives from plein ("to sail") because of the cluster's importance in delimiting the sailing season in the Mediterranean Sea.
Galileo Galilei was the first known astronomer to view the Pleiades through a telescope. He thereby discovered that the cluster contains many stars too dim to be seen with the naked eye. He published his observations, including a sketch of the Pleiades showing 36 stars, in his treatise Sidereus Nuncius in March 1610.
Charles Messier measured the position of the cluster and included it as M45 in his catalogue published in 1771.
INSTRUMENT Canon EF 70-200mm F/2.8 II
CAMERA Canon EOS 60Da
MOUNT Vixen Sphinx
GUIDING Lacerta MGen Autoguider
EXPOSURE TIME 148x5min iso 800
LOCATION Kékestető, Ágasvár, Zselic Starpark
