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Ursa Minor (Latin: "Smaller She-Bear", contrasting with Ursa Major), also known as the Little Bear, is a constellation in the northern sky. Like the Great Bear, the tail of the Little Bear may also be seen as the handle of a ladle, hence the name Little Dipper. It was one of the 48 constellations listed by the 2nd-century astronomer Ptolemy, and remains one of the 88 modern constellations. Ursa Minor has traditionally been important for navigation, particularly by mariners, due to Polaris being the North Star. Polaris, the brightest star in the constellation, is a yellow-white supergiant and the brightest Cepheid variable star in the night sky, ranging from apparent magnitude 1.97 to 2.00. Beta Ursae Minoris, also known as Kochab, is an aging star that has swollen and cooled to become an orange giant with an apparent magnitude of 2.08, only slightly fainter than Polaris. Kochab and magnitude 3 Gamma Ursae Minoris have been called the "guardians of the pole star".〔 Planets have been detected orbiting four of the stars, including Kochab. The constellation also contains an isolated neutron star—Calvera—and H1504+65, the hottest white dwarf yet discovered with a surface temperature of 200,000 K. ==History and mythology== In the Babylonian star catalogues, Ursa Minor was known as MAR.GID.DA.AN.NA, the Wagon of Heaven, Damkianna. It appeared on a pair of tablets containing canonical star lists that were compiled around 1000 BC, the MUL.APIN, and was one of the "Stars of Enlil"—that is, the northern sky. The possible origin of its name was its appearing to rotate like a wheel around the north celestial pole. The first mention of Ursa Minor in Greek texts was by philosopher Thales of Miletus in the 6th century BC. He pointed out that it was a more accurate guide to finding true north than Ursa Major. This knowledge had reportedly come from the Phoenicians in the eastern Mediterranean, and the constellation bore the term ''Phoenikē''. Homer had previously only referred to one "bear", raising the question of what he saw the stars of Ursa Minor as, or whether they were recognised at all. Ursa Minor and Ursa Major were related by the Greeks to the myth of Callisto and her son Arcas, both placed in the sky by Zeus.〔 However, in a variant of the story, in which it is Boötes that represents Arcas, Ursa Minor represents a dog. This is the older tradition, which explains both the length of the tail and the obsolete alternate name of ''Cynosura'' (the dog's tail) for Polaris, the North Star. Cynosura is also described as a nurse of Zeus, honoured by the god with a place in the sky.〔 An alternate myth tells of two bears that saved Zeus from his murderous father Cronus by hiding him on Mount Ida. Later Zeus set them in the sky, but their tails grew long from being swung by the god. Because Ursa Minor consists of seven stars, the Latin word for "North" (i.e. where Polaris points) is ''septentrio'', from ''septem'' (seven) and ''triones'' (oxen), from seven oxen driving a plow, which the seven stars also resemble. This name has also been attached to the main stars of Ursa Major.〔 Ursa Minor has traditionally been important for navigation, particularly by mariners, due to Polaris being the North Star. Polaris is less than one degree away from the north celestial pole (hence the alternative name Pole Star) so its position in the sky is largely unaffected by the rotation of the Earth. From any point in the Northern Hemisphere the direction to Polaris is always north and its angular altitude is roughly equal to the latitude. In Inuit astronomy, the three brightest stars—Polaris, Kochab and Pherkad—were known as ''Nuutuittut'' "never moving", though the term is more frequently used in the singular to refer to Polaris alone. The Pole Star was too high in the sky at far northern latitudes to be of use in navigation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ursa Minor」の詳細全文を読む スポンサード リンク
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