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Cassiopeia is a constellation in the northern sky, named after the vain queen Cassiopeia in Greek mythology, who boasted about her unrivalled beauty. Cassiopeia was one of the 48 constellations listed by the 2nd-century Greek astronomer Ptolemy, and it remains one of the 88 modern constellations today. It is easily recognizable due to its distinctive 'M' shape when in upper culmination but in higher northern locations when near lower culminations in spring and summer it has a 'W' shape, formed by five bright stars. It is bordered by Andromeda to the south, Perseus to the southeast, and Cepheus to the north. It is opposite the Big Dipper. In northern locations above 34ºN latitude it is visible year-round and in the (sub)tropics it can be seen at its clearest from September to early November in its characteristic 'M' shape. Even in low southern latitudes below 25ºS is can be seen low in the North. ==Notable features== The four brightest stars of Cassiopeia are all brighter than the third magnitude. * Alpha Cassiopeiae, traditionally called ''Shedir'' (from the Arabic ''Al Sadr'', "the breast"), is a double star. The primary is an orange-hued giant of magnitude 2.2, 229 light-years from Earth. The secondary is widely separated from the primary and is of magnitude 8.9. * Beta Cassiopeiae, or ''Caph'' (meaning "hand"), is a white-hued star of magnitude 2.3, 54 light-years from Earth. 16th-century Arabian astronomer Al Tizini gave this star the name ''Al Sanam al Nakah'', (The Camel's Hump), referring to the contemporaneous Persian figure.〔Richard H. Allen (1889) Star Names, p. 146 (see also http://www.constellationsofwords.com/stars/Caph.html).〕 * The two other notably bright stars in Cassiopeia are both variable stars. Gamma Cassiopeiae is a shell star, a type of variable star that has a very high rate of rotation. This causes the star to be somewhat unstable and periodically eject rings of material. Gamma Cassiopeiae has a minimum magnitude of 3.0 and a maximum magnitude of 1.6; it is currently approximately magnitude 2.2. * Delta Cassiopeiae, also known as "Ruchbah" or "Rukbat," meaning "knee," is an Algol-type eclipsing variable star. It varies by 0.1 magnitudes around magnitude 2.7; its period is 2 years and 1 month. Ruchbah appears to have a blue-white hue and it is 99 light-years from Earth. There are several dimmer single stars in Cassiopeia. Epsilon Cassiopeiae is a blue-white hued star of magnitude 3.3, 442 light-years from Earth. Rho Cassiopeiae is a semi-regular pulsating variable yellow-hued supergiant star, among the most luminous stars in the galaxy with a luminosity of approximately 500,000 solar luminosities. It has a minimum magnitude of 6.2 and a maximum magnitude of 4.1; its period is approximately 320 days. Rho Cassiopeiae is about 10,000 light-years from Earth. Cassiopeia possesses several dimmer double stars and binary stars. Eta Cassiopeiae is a binary star with a period of 480 years. The primary is a yellow-hued star of magnitude 3.5 and the secondary is a red-hued star of magnitude 7.5. The system is 19 light-years from Earth. Iota Cassiopeiae is a triple star 142 light-years from Earth. The primary is a white-hued star of magnitude 4.5, the secondary is a yellow-hued star of magnitude 6.9, and the tertiary is a star of magnitude 8.4. The primary and secondary are close together but the primary and tertiary are widely separated. Sigma Cassiopeiae is a binary star 1500 light-years from Earth. It has a green-hued primary of magnitude 5.0 and a blue-hued secondary of magnitude 7.3. Psi Cassiopeiae is a triple star 193 light-years from Earth. The primary is an orange-hued giant star of magnitude 4.7 and the secondary is a close pair of stars that appears to be of magnitude 9.0. 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「Cassiopeia (constellation)」の詳細全文を読む スポンサード リンク
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