Antares (α Scorpii, α Sco, Alpha Scorpii) is a red supergiant star in the Milky Way galaxy and the sixteenth brightest star in the nighttime sky. (It is sometimes listed as 15th brightest, if the two brighter components of the Capella quadruple star system are counted as one star.) Along with Aldebaran, Spica, and Regulus it is one of the four brightest stars near the ecliptic. It is the brightest star in the constellation Scorpius, and is often referred to as "the heart of the scorpion". Antares is a slow variable star with an average magnitude of +1.09.[3]
Antares is a supergiant star with a stellar classification of M1.5Iab-b.[3] It has a radius of approximately 883 times that of the Sun;[6] if it were 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 550 light-years (170 parsecs) from the Earth.[1] 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 is calculated to be 15 to 18 solar masses.[10]
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).[11] This leads to a radius of 822 ± 80 solar radii.[clarification needed]
Antares is a type LC slow irregular variable star, whose apparent magnitude slowly varies from +0.88 to +1.16.[4]
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. 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;[12] 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.
Excerpt from Wikipedia.