In order to see this week’s featured star pattern you’ll need to find a spot with a southern horizon fairly free of trees. After it gets good and dark after 9 PM, look for the brightest star about an open hand span above the southern horizon. It will have bit of a reddish tint. Congratulations, you’ve found Antares. The combination of distance and luminosity make it the fifteenth brightest star in our sky.
Antares is huge. It is about 700 times the diameter of our Sun. All the inner planets out to Mars would fit inside it. Antares’ atmosphere extends even farther out. It extends so far out that the whole solar system would be engulfed if it were in our Sun’s place. Its reddish tint is due to its “cool” surface temperature. It’s half as hot as our Sun at only 5,000 degrees! This red supergiant star is about 500 light years away. (Remember, a light year is 25 trillion miles!)
Antares is an irregular pulsating star. It can expand and contract by 25% and double its brightness as it does so. Antares also has a companion star orbiting it, but it is much dimmer and close to Antares. You won’t see it even with good binoculars.
The lifecycle of a supergiant star is amazing. They are very rare. Far less than 1% of stars are born this big, and, like in the old song, they “live fast and die young”. Even though they have ten times more hydrogen fuel to burn than stars like our sun, they fuse it hundreds of times faster. Although Antares formed only about 10 million years ago, it will die in a supernova explosion in about a million years. Its corpse will be a neutron star or a black hole! Our Sun’s lifetime will be about ten billion years. That’s a thousand times longer than Antares.
Now that you know more than you may have wanted to know about Antares, how do we find its constellation? It’s in Scorpius, the scorpion. Antares represents its heart. It is one of the few constellations that actually look like their namesake. Look down and to the left of Antares and see a curving fishhook line of stars that make the scorpion’s tail and stinger. To the right of Antares is a line of 3 stars that represent the scorpion’s head. (See the image.)
If you keep going up and to the right from Antares and the three “head” stars you’ll come to two stars in the small constellation Libra. These stars used to be part of Scorpius, and their names in Arabic reflect this history. Their names are fun to roll off the tongue. Zubeneschamali (the northern claw) and Zubenelgenubi (the southern claw)
Finally, where did the name Antares come from? Anti from against or rival of, and Ares from the Greek name for the red planet Mars. Every couple of years, as Mars orbits the Sun, it appears to pass near Antares and they can easily be confused with each other. So, Antares = rival of Mars.
For questions or comments: James Hill, Mississippi NASA/JPL Solar System Ambassador. jhill6333@gmail.com
