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Crux is a constellation located in the southern sky in a bright portion of the Milky Way, and is the smallest but one of the most distinctive of the 88 modern constellations. Its name is Latin for cross, and it is dominated by a cross-shaped or kite-like asterism that is commonly known as the Southern Cross. Predominating the asterism is the most southerly and brightest star—the blue-white Alpha Crucis or Acrux—followed by four other stars, descending in clockwise order by magnitude: Beta, Gamma (one of the closest red giants to Earth), Delta and Epsilon Crucis. Many of these brighter stars are members of the Scorpius–Centaurus Association, a large but loose group of hot blue-white stars that appear to share common origins and motion across the southern Milky Way. Two star systems have been found to have planets. The constellation also contains four Cepheid variables visible to the naked eye under optimum conditions. Crux also contains the bright and colourful open cluster known Jewel Box (NGC 4755), and to the southwest, the extensive dark nebula known as the Coalsack Nebula. ==History== Crux was known to the Ancient Greeks due to the fact that it can be seen from southern Egypt; Ptolemy, who regarded it as part of the constellation Centaurus.〔Pasachoff, (''Stars and Planets'' ), 2006, p. 144.〕 It was entirely visible as far north as Britain in the fourth millennium BC. However, the precession of the equinoxes gradually lowered its stars below the European horizon, and they were eventually forgotten by the inhabitants of northern latitudes. By AD 400, most of the constellation never rose above the horizon for Athenians. The 15th-century Venetian navigator Alvise Cadamosto made note of what was probably the Southern Cross on exiting the Gambia River in 1455, calling it the ''carro dell'ostro'' ("southern chariot"). However, Cadamosto's accompanying diagram was inaccurate.〔"We likewise observed...due south by compass, a constellation of six large bright stars, in the figure of a cross in this form...we conjectured this to be the southern chariot, but could not expect to observe the principal star, as we had not yet lost sight of the north pole." A. Cadamosto ''Navigatione'', written c.1465 (1550 Ramusio edition, (p.116r ); 1811 Kerr edition (p.244 )). However, note a the manuscript of Cadamosto's notebook has not survived, only the printed version, and the errors in the diagram may be due to the printer's decision.〕〔Dekker, Elly (1990). ''Annals of Science'', vol. 47, pp. 530–533.〕 Historians generally credit João Faras - astronomer and physician of King Manuel I of Portugal who accompanied Pedro Álvares Cabral in the discovery of Brazil in 1500 - for being the first European to depict it correctly. Faras sketched and described the constellation (calling it "Las Guardas") in a letter written on the beaches of Brazil on May 1, 1500, to the Portuguese monarch.〔Dekker, Elly (1990). ''Annals of Science'', vol. 47, pp. 533–535.〕 Explorer Amerigo Vespucci seems to have observed not only the Southern Cross but also the neighboring Coalsack Nebula on his second voyage in 1501–02.〔Dekker, Elly (1990). ''Annals of Science'', vol. 47, pp. 535–543.〕 Another early modern description clearly describing Crux as a separate constellation is attributed to Andreas Corsali, an Italian navigator who from 1515 to 1517 sailed to China and the East Indies in an expedition sponsored by King Manuel I. In 1516, Corsali wrote a letter to the monarch describing his observations of the southern sky, which included a rather crude map of the stars around the south celestial pole including the Southern Cross and the two Magellanic Clouds seen in an external orientation, as on a globe.〔Dekker, Elly (1990). ''Annals of Science'', vol. 47, pp. 545–548.〕 Emery Molyneux and Petrus Plancius have also been cited as the first uranographers to distinguish Crux as a separate constellation; their representations date from 1592, the former depicting it on his celestial globe and the latter in one of the small celestial maps on his large wall map. Both authors, however, depended on unreliable sources and placed Crux in the wrong position. Crux was first shown in its correct position on the celestial globes of Petrus Plancius and Jodocus Hondius in 1598 and 1600. Its stars were first catalogued separately from Centaurus by Frederick de Houtman in 1603.〔(【引用サイトリンク】 title=Ian Ridpath’s Star Tales – Crux )〕 Later adopters of the constellation included Jakob Bartsch in 1624 and Augustin Royer in 1679. Royer is sometimes wrongly cited as initially distinguishing Crux. 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「Crux」の詳細全文を読む スポンサード リンク
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