Thanks to James B. Kaler. These contents are the property of the author and are reproduced from original without the author's express consent because of fair use and valid educational purposes.
ANTARES
A brilliant jewel set within the Summer Milky Way, Antares guides us to one of the great constellations of the sky, the zodiac's Scorpius (or Scorpio), the celestial scorpion, one of the few constellations that actually looks like what it represents. Antares, gleaming redly at the scorpion's heart, has a color similar to Mars. Since it is found within the zodiac, which contains the apparent path of the Sun and planets, it is commonly mistaken for the red planet, a fact shown by its name, Antares, or "Ant-Ares," which means "like Mars," "Ares" being the Greek name for the god of war. This magnificent first magnitude star, shining opposite Betelgeuse, its counterpart in Orion, is the 13th brightest in the sky even though at a great distance of 600 light years, revealing that it is truly luminous, to the eye over 12,000 times brighter than the Sun. Because it is cool, only about 3400 degrees Kelvin at its surface, it radiates a considerable amount of its light in the invisible infrared. When that is taken into account, the star becomes almost 40,000 times brighter than the Sun. A low temperature coupled with high luminosity tells us that the star must be huge, so big that astronomers can actually detect and measure the size of its apparent disk. If placed at the Sun, the star, aptly called a supergiant, would extend outward for over 4 Astronomical Units (the distance between the Earth and Sun) and therefore 4/5 the way to the planet Jupiter. The star is slowly evaporating under a fierce wind that blows from its surface and that has encased it in a small gas cloud or nebula. Ordinarily, such a nebula (common among such supergiants) would not be visible to the eye, but in the case of Antares, the cloud is illuminated by the light of a hot companion star that at fifth magnitude hides closely within Antares' bright glare. Antares probably does not have much time left to it. It is massive enough someday to develop an iron core and eventually to explode as a brilliant supernova long before it would ever have a chance to evaporate completely. The event may be a million years off, an astronomical blink of an eye; or it may occur tonight, so keep a watch on one of the great stars of the nighttime sky.