The brilliant stars seen in this image are members of the popular open star cluster known as the Pleiades, or Seven Sisters. The Hubble Space Telescope's Fine Guidance Sensors refined the distance to the Pleiades at about 440 light-years. The Fine Guidance Sensors are at the periphery of Hubble's field-of-view. They trace a circumference that is approximately the angular size of the Moon on the sky. They are overlaid on this image to give a scale to Hubble's very narrow view on the heavens.
Hubble Fine Guidance Sensors measured slight changes in the apparent positions of three stars within the cluster when viewed from different sides of Earth's orbit. Astronomers took their measurements six months apart over a 2 1/2-year period. About 1,000 stars comprise the cluster, located in the constellation Taurus.
The color-composite image of the Pleiades star cluster was taken by the Palomar 48-inch Schmidt telescope. The image is from the second Palomar Observatory Sky Survey, and is part of the Digitized Sky Survey. The Pleiades photo was made from three separate images taken in red, green, and blue filters. The separate images were taken between Nov. 5, 1986 and Sept. 11, 1996.