star in the Pleiades, thought to be typical of the shell stars, so called because in their rapid rotation they throw off shells of gas. In 1938 sudden changes in the spectrum of Pleione were attributed to the ejection of a gaseous shell, which by 1952 had apparently dissipated. Pleione is a blue-white star of about the fifth magnitude. Some astronomers conjecture that it may have been brighter in the past; it would then have made a seventh bright star in the Pleiades cluster, which is named for seven mythological sisters.