06-29-2009 - brightest stars

How to see it

Bright reddish Antares, also known as Alpha Scorpii is well known as the ruby Heart of the southern constellation Scorpius the Scorpion. It is the 16th brightest star in the sky. Antares is easy to spot. It’s brightest – and distinctly orange – in the fishhook-shaped pattern of the Scorpion. This constellation is distinctive in the south in the early evening from late spring to early fall.

This star is much better known to northern hemisphere residents than several brighter southerly stars because it is visible from just about anywhere in the northern hemisphere short of the Arctic. Well, not quite the Arctic, but anywhere south of 63 degrees north latitude can — at one time or another — see Antares (Helsinki yes, Fairbanks, no!).

The midnight culmination of Antares is on or near June 1 —- that is when Antares is highest in the sky at midnight (midway between sunset and sunrise). It is highest in the sky at about dawn in early March and at about sunset in early September. Antares is in the southern half of the sky, so the chance of observation on any given night increases with increasing southern latitude. From about 67 degrees south latitude, Antares is circumpolar, meaning that it never sets and is visible every night of the year.

Antares is virtually the same brightness as Spica in the constellation Virgo, and sometimes Spica is listed as the 16th brightest and Antares the 15th brightest.

History and Myth

Antares is Greek for “Opposing Mars” or “Rivaling Mars.” The first part, “Ant” is from the same root as “anti”, and Greek name of Mars is “Ares.” So Antares is the “Anti-Mars” as a rival or as if to deceive — an imposter! Antares is the same general color as Mars, but for a few months every couple of years the planet is much brighter than the star. Most of the time, though, Mars is near the same brightness or fainter than Antares. Every couple of years Mars passes near Antares, which was perhaps seen as taunting the star, as Mars moves rapidly through the heavens and Antares, like all stars, seems fixed to the starry firmament. Both the Arabic and Latin names for the star mean “heart of the Scorpion,” which it the way it is situated in most constellation drawings.

As is typical, more mythology attends the full constellation of Scorpius than the star Antares. Perhaps the most well known story of Scorpius is that the Earth goddess, Gaia, sent him to sting arrogant Orion, who had claimed his intent to kill all animals on the planet. Scorpius killed Orion, and both were placed in the sky, although in opposite sides of the heavens, positioned as if to show the Scorpion chasing the Mighty Hunter.

Interestingly, Betelgeuse in the constellation Orion is similar in appearance to Antares, although brighter. Betelgeuse is not as associated with Mars as is Antares. Although the planet passes in the vicinity of Betelgeuse every couple of years, it never gets as close as it does to Antares.

In Polynesia, Scorpius is often seen as a fishhook, with some stories describing it as the magic fishhook used by the demigod Maui to pull up land from the ocean floor that became the Hawaiian islands. According to the University of Hawaii’s Institute for Astronomy website, the Hawaiian name for Antares, Lehua-kona, seems to have little to do with the constellation. It means “southern lehua blossom.”

Science

Antares is an M1 supergiant star, similar to but somewhat larger than Betelgeuse. Hipparcos data puts Antares at about 604 light-years, compared to Betelgeuse’s 428 light-years, explaining why the larger star appears slightly fainter from earth. Antares is truly an enormous star, with a radius in excess of 3 Astronomical Units (AU). One AU is the Earth’s average distance from the sun. If by some bit of magic Antares was suddenly substituted for our sun, the surface of the star would extend well past the orbit of Mars!

The “M1” designation says that Antares is reddish in color and “cooler” than many other stars, with a surface temperature of 3500 kelvins (about 5800 degrees F, compared to about 10,000 degrees F for the sun) can be called “cool.” Even though the temperature is relatively low, Antares’ tremendous surface area from which light can escape makes it very bright. In fact, it approaches 11,000 times the brilliance of our puny G2 star — but that is just in visible light. When all wavelengths of electromagnetic radiation is considered, Antares pumps out more than 60,000 times the energy as does our sun!

Like all M-type giants and supergiants, Antares is close to the end of its lifetime. Someday soon (astronomically speaking), it will effectively run out of fuel and collapse. The resulting infall of its enormous mass, some 15-18 times solar, will cause an immense supernova explosion, ultimately leaving a tiny neutron star or possibly a black hole. This explosion, which could be tomorrow or millions of years from now, will be spectacular as seen from earth, but we are far enough away that there likely is no danger to our planet.

Antares’ position is RA:16h 29m 24s, dec: -26° 25’ 55”.

Written by Larry Sessions

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