June 1, 2004: Astronomers using NASA's Hubble Space Telescope have helped settle a mystery that has puzzled scientists concerning the exact distance to the famous nearby star cluster known as the Pleiades, or the Seven Sisters. The Pleiades cluster, named by the ancient Greeks, is easily seen as a small grouping of stars lying near the shoulder of Taurus, the Bull, in the winter sky. Although it might be expected that the distance to this well-studied cluster would be well established, there has been an ongoing controversy among astronomers about its distance for the past seven years.See the rest:
It is a group of anywhere from several hundred to a million or more stars. Star clusters come in two types: open clusters and globular clusters. In general, stars in a cluster were born at the same time out of the same cloud of interstellar gas.
The Pleiades is an open cluster, which contains up to several thousand stars distributed in a region a few light-years across. Cluster stars are more spaced out than in globular clusters. Open clusters are found only in the disks of galaxies and often contain young stars.
Calculating accurate measurements to nearby stars is crucial in obtaining accurate distances to faraway objects. Astronomers have only one direct means for gauging distances to stars, called the parallax method. With current telescopes, this method gives accurate results only for distances up to about 500 light-years. Distances beyond that limit must be determined by indirect methods, based on comparing the brightness of distant stars with those of nearer ones of the same type, and making the assumption that both objects have the same intrinsic, or true, brightness. Astronomers can build up a "distance ladder," based on ever-farther objects, ultimately leading to the use of supernovae as "standard candles" for the most distant reaches of the universe.