Jimmy Westlake's Celestial News column appears Tuesdays in the Steamboat Today.
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Steamboat Springs Among the 20 brightest stars in the sky, there are only two red supergiant stars. One is the star Betelgeuse, visible in the wintertime as the shoulder star of Orion the Hunter. The other is a star named Antares, visible right now in the early summer sky as the heart of Scorpius the Scorpion.
The name Antares comes from the Greek words meaning "the rival of Ares." Ares was the Greek equivalent of Mars, the Roman mythological god of war. Antares and Mars shine with an unmistakable reddish color, and beginning sky watchers sometimes make the mistake of misidentifying Antares as the planet Mars. One way to tell the difference is to recall the old rule of thumb that stars twinkle and planets don't. After all, the song says "twinkle-twinkle little star" not "twinkle-twinkle little planet."
Antares is one of the largest stars known in our galaxy. It is in the advanced stages of its life and has ballooned outward to a size 800 times larger than our Sun. If placed at the sun's location in the center of our solar system, Antares would swallow the orbits of all of the inner planets, Mercury, Venus, Earth, and Mars.
Antares is a cool, red supergiant star nearing the end of its life. Within its core, Antares is furiously fusing helium atoms into carbon atoms, a sure sign of advanced age in a giant star. Enjoy Antares now because it probably doesn't have much time left to live. One day, in the not-too-distant future, Antares will have fused all of its helium into carbon, all of its carbon into silicon, and all of its silicon into iron. The iron core of the Scorpion's heart suddenly will collapse inward under its own tremendous weight and trigger a catastrophic supernova explosion. If anything remains of the Scorpion's heart after this colossal explosion, it will either be a rapidly spinning neutron star, or a bottomless pit in the fabric of spacetime called a black hole. Either way, the heart of the Scorpion will be dead.
A beautiful globular star cluster called M4 lies in the same binocular field as Antares. This swarm of tens of thousands of stars lies 7,200 light years from Earth. Look for it just to the west of Antares. You might also glimpse another fainter globular star cluster, NGC 6144, just north of Antares.
Antares itself is a binary star, with a fainter green companion that can be glimpsed through a telescope of aperture 6-inches or larger. The two stars orbit each other once every 878 years.
Look for Antares almost due south in the sky about 11:00 p.m. on July evenings.