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Ursa Minor (Little Bear) is a constellation in the northern sky. In North America, it is also known as the Little Dipper since its seven main stars appear to form a ladle shape (diagram pictured). One of 88 modern constellations, it was also one of 48 listed by 2nd-century astronomer Ptolemy. Polaris, its brightest star, is currently less than one degree away from the north celestial pole. Because this position stays nearly fixed as the Earth rotates, the star has been important for navigation, particularly by mariners. Polaris is a yellow-white supergiant and the brightest Cepheid variable star, ranging in apparent magnitude (m) from 1.97 to 2.00. Beta Ursae Minoris, also known as Kochab, has swollen and cooled to become an orange giant with a slightly fainter m of 2.08. Ursa Minor also contains an isolated neutron star—Calvera—and H1504+65, the hottest known white dwarf, with a surface temperature of 200,000 K. Planets have been detected orbiting four of its stars, including Kochab. (Full article...)