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Antares, () also known by its Bayer designation Alpha Scorpii (abbreviated to α Scorpii or α Sco), is the fifteenth brightest star in the nighttime sky and the brightest star in the constellation Scorpius, and is often referred to as "the heart of the scorpion". Along with Aldebaran, Regulus, and Fomalhaut, Antares comprises the group known as the 'Royal stars of Persia'. It is one of the four brightest stars near the ecliptic. Distinctly reddish when viewed with the unaided eye, Antares is a red supergiant of spectral type M0.5Iab and is one of the largest and most luminous observable stars. It is a slow irregular variable star with the quoted magnitude of +0.96. Antares is the brightest, most massive, and most evolved stellar member of the nearest OB association (the Scorpius-Centaurus Association). Antares is a member of the Upper Scorpius subgroup of the Scorpius-Centaurus Association, which contains thousands of stars with mean age 11 million years at a distance of approximately 145 parsecs (470 light years).〔 ==Properties== Antares is a supergiant star with a stellar classification of M0.5Iab.〔 With a radius that is approximately 883 times that of the Sun,〔 if placed in the center of our Solar System, its outer surface would lie between the orbits of Mars and Jupiter. Based upon parallax measurements, Antares is approximately from the Earth.〔 Its visual luminosity is about 10,000 times that of the Sun, but because the star radiates a considerable part of its energy in the infrared part of the spectrum, the bolometric luminosity equals roughly 65,000 times that of the Sun. The mass of the star has been calculated to be in the range of 15 to 18 solar masses. A recent analysis comparing the effective temperature and luminosity of Antares to theoretical evolutionary tracks for massive stars which include rotation and mass loss yielded a mass of approximately 17 solar masses and age of 12 million years old. The size of Antares may be calculated using its parallax and angular diameter. The parallax angle is given in the box to the right, and the angular diameter is known from lunar occultation measurements (41.3 ± 0.1 mas). This implies a radius of 890 ± 150 solar radii at this distance. By analysing its radial velocity from its spectrum, Pugh and colleagues calculated a period of 5.93 ± 0.01 years and considered whether this change was orbital or pulsational. If the latter, then the radius of the star changes by 165 ± 22 solar radii (19% ± 4%). However, if this were the case, Antares' brightness would vary by a greater amount. Antares is a type ''LC'' slow irregular variable star, whose apparent magnitude slowly varies from +0.6 to +1.6. Antares is visible in the sky all night around May 31 of each year, when the star is at opposition to the Sun. At this time, Antares rises at dusk and sets at dawn as seen at the equator. For approximately two to three weeks on either side of November 30, Antares is not visible in the night sky, because it is near conjunction with the Sun;〔 ((2009, ) (2010, ) (2011) )〕 this period of invisibility is longer in the Northern Hemisphere than in the Southern Hemisphere, since the star's declination is significantly south of the celestial equator. 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「Antares」の詳細全文を読む スポンサード リンク
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