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M45 is an open star cluster located in the constellation of Taurus, the Bull. It is about 440 light years from our solar system. This open cluster, also known as the Pleiades and the Seven Sisters, contains at least 500 stars. The blue nebula that appears to surround this star cluster is a reflection nebula. Light from the stars in the cluster shines through and reflects off a cold cloud of gas and dust in space.

The distance to the Pleiades was recently accurately measured with the Palomar Testbed Interferometer.

The cluster is an easy object to see even without a telescope. In 1769 Charles Messier made it the forty fifth object, M45, of his famous catalog.

This image is a composite from two black and white images taken with the Palomar Observatory's 48-inch (1.2-meter) Samuel Oschin Telescope as a part of the Second Palomar Observatory Sky Survey ( POSS II). The images were recorded on two glass photographic plates - one sensitive to red light and the other to blue. The plates were scanned and color combined to produce the image seen here.

The Samuel Oschin Telescope was used to generate the Second Palomar Observatory Sky Survey POSS II and the Digital Palomar Observatory Sky Survey DPOSS. Plates for the POSS II survey were donated by the Eastman Kodak Corporation.

The POSS II survey was enabled by grants from the Alfred P. Sloan Foundation, the National Geographic Society, and the National Science Foundation. Partial funding for the DPOSS survey was provided by the Norris Foundation.
Plates were scanned at the Space Telescope Science Institute, and the results catalogued at Caltech.

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