The Pleiades catalogued as M45 by Charles Messier (also known as "The Seven Sisters" or "Subaru" in Japanese) is one of the nearest star clusters and easily recognizable without optical aid. The open star cluster is part of the constellation Taurus, The Bull, and therefore best visible during winter months in the northern hemisphere and during summer months downunder.
The Pleiades spanning over nearly four full moon widths are a rewarding view in low-power, wide-field binoculars, such as 7x50 or 10x50 optics. They are also used for measuring eye sight. Your eyes are in good condition if you recognize 7 stars, namely the "seven sisters": Alcyone, Atlas, Electra, Maia, Merope, Taygeta and Pleione - so the saying goes.
Since the Pleiades are located near the ecliptic they are often occulted by the moon and the planets. The image at the right whitnesses such an event occurred on April 1, 2004.
The cluster is believed to contain over 3000 stars, most of them blueish in color with high surface temperatures and an estimated average age of just 115 million years, in a distance of approximately 440 light-years. Being more massive and larger in diameter, the brightest stars outshine the sun several hundred times in luminosity.
Though not surprising for a star cluster, some stars are relatively close to each other. For instance, the distance between Maia and Merope spans over a mere 2.8 light-years (the nearest star to our sun is 4.4 light-years away).
Explore the Pleiades with a pair of binoculars. But behold, you will not see the entire glory with nebulosity and colors as on the photo at the top, which is the result of longer exposure. Your eyes are not capable of accumulating light like film or CCDs. A realistic and typical image of the Pleiades through binoculars is shown at the left. The darker the observation site, the more stars are revealed in the given field of view.