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Antares: Red Star at the End of Its Life

Doorstep Astronomy: Moon and Antares Get Close
The moon often visits the bright red star Antares in Scorpius.
Credit: Starry Night Software

Antares is a red supergiant star that is nearing the end of its life. Once there is no more fuel left to burn, the star will collapse and explode into a supernova — "at which time its brightness will rival that of the rest of our galaxy put together," noted astrophysicists Paul Butterworth and Mike Arida for NASA's Imagine the Universe!

The star is among the 20 brightest visible in Earth's night sky, although its brightness varies. Amateur observers have pegged its apparent magnitude between 0.88 and 1.16. Additionally, it has a small neighbor star (Antares B) that looks bluish-white and is sometimes called "a little spark of glittering emerald." [The Brightest Stars in the Sky: A Starry Countdown]

In modern rocketry, Antares was the name of the lunar lander on the Apollo 14 moon mission, and it is also the name of a rocket being developed by Orbital Sciences Corp.

Locating Antares

Antares, also called alpha Scorpii, is a prominent star in Scorpius (the Scorpion), a constellation that is visible in the southern night sky of most locations in the Northern Hemisphere. Antares is about 604 light-years from Earth. It is 700 times the sun's diameter, large enough to engulf the orbit of Mars, if the solar system were centered on it.

Despite its size, the overall density of Antares is less than one-millionth that of the sun. Antares is also relatively cool as stars go, only about 6,500 F (3,593 C) compared to 11,000 F (6,093 C) for the sun. The star's low temperature accounts for its ruddy color.

Antares' position is:

  • Right ascension: 16 hours 29 minutes 24.4 seconds
  • Declination: -26 degrees 25 minutes 55 seconds

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Antares in history

The word "Antares" means "anti-Ares" or "anti-Mars," likely because astronomers in ancient times thought the reddish star looked similar to the red planet. The planet, in fact, can sometimes get close to Antares in the Red Planet's travels across the night sky.

Antares' bright appearance got attention in many older cultures, according to Richard Hinckley Allen's "Star Names and Their Meanings." In Persia around 3000 B.C., it was named one of four royal stars in the sky. In Egypt, Antares was a symbol of the goddess Selkit (who is often referred to as the Scorpion Goddess.)

The star is so bright that it washed out its fainter companion, meaning that Antares B was not discovered until well into the telescopic age. Johann Tobias Bürg, an Austrian astronomer, spotted the fifth-magnitude star on April 13, 1819 when the moon covered Antares.

Antares in modern times

According to NASA, the star has eaten all its hydrogen and is now shining because it is fusing progressively heavier elements. Time-exposure pictures of the region around Antares reveal an unusually colorful area of gas: yellow, blue and red are all prominent in 2004 pictures from the Royal Observatory in Edinburgh and the Anglo-Australian Observatory.

This is due to a combination of gases whose atoms are excited by starlight, and light shining from Antares A and B, NASA said. Additionally, the area has several other objects crowding the field of view: the nebula (gas cloud) Rho Ophiuchi and M4, a globular cluster (or collection of stars.)

Antares was the inspiration for the name of a rocket now being tested by Orbital Sciences. On April 21, 2013, the private company's rocket launched into space for the first time from Virginia's Mid-Atlantic Regional Spaceport (MARS), which is located at NASA's Wallops Flight Facility.

The company aims to launch its Cygnus spacecraft aboard Antares to the International Space Station later in 2013.

— Elizabeth Howell, SPACE.com Contributor

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