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(20 Tauri). The Pleiades, the Seven Sisters star cluster (one of two naked eye clusters that belong to Taurus, the other the Hyades), twinkle high in northern hemisphere autumn and winter skies, while shining closer to the horizon in the skies of southern hemisphere spring and summer. Maia, a proper name, is one of the seven mythical daughters of Atlas and Pleione. Shining at bright third magnitude (3.87) from a distance of 385 light years, she ranks fourth brightest after Alcyone, Atlas, and Electra. Except for Alcyone (Eta Tauri), the Pleiades' stars carry only Flamsteed numbers, Maia number 20 in the west-to-east parade of numbered naked-eye stars within the celestial Bull. A blue-white class B (B8) giant star, Maia radiates 660 times more energy than does the Sun from a warm surface with a rather uncertain temperature of 12,600 Kelvin. Its radius of 5 1/2 times that of the Sun gives it true giant status, although the giants in these hotter stars are nowhere near as large as their cooler orange cousins like Arcturus and Aldebaran (which lies in front of the Hyades). As a giant, Maia either has shut down its internal hydrogen fusion or will do so very shortly, its mass of a bit over four times that of the Sun giving the star a destiny as a massive white dwarf. Like the other stars of the cluster, Maia is involved with the Pleiades reflection nebula that peaks around Merope. Maia appears to be a relatively slow rotator, and as such has a fairly quiet atmosphere. As a result, different kinds of atoms drift downward under the pull of gravity, whereas others are lofted upward by radiation, the effects making Maia one of the "mercury-manganese stars," in which these two and other chemical elements are greatly enhanced (manganese in Maia up by a factor of 160 compared with hydrogen). The star also has a bit of a curious history. Fifty years ago, the great astronomer Otto Struve suggested that Maia was slightly variable, with a period of a few hours. It thence became the prototype of a whole class of "Maia variables" that included Pherkad (Gamma Ursae Minoris) and that were in an otherwise stable realm of temperature and luminosity. Astronomers have argued since then about the reality of the class. Only recently has the issue been put to rest, when the prototype (and some others) were found to be stable and not varying at all (though others in the purported class do vary for other reasons)