Antares

Antares is a yellow-orange supergiant star 600 light-years away in the constellation Scorpius.

The star Antares marks the "heart" of Scorpius, the scorpion. It is the brightest star in Scorpius. It's the most difficult to see in the early twilight, but as the sky gets darker, it stands out more. Antares also stands out because of its color. While most of the stars show little or no color, Antares is a vivid orange. That's the result of its surface temperature, which is thousands of degrees cooler than the Sun. But Antares is a supergiant star -- one of the biggest and most massive in our part of the galaxy -- so its interior is millions of degrees hotter than the Sun's interior. Like most supergiants, Antares is likely to end its life with a bang -- it'll explode as a supernova. That could happen anytime within the next few million years -- or as early as tonight.

Antares is a type of star known as a red supergiant. Among other things, that means the star is nearing the end of its life. It's used up the hydrogen in its core, and it's "burning" through a succession of heavier elements. This process causes the core to shrink, so it relaxes its grip on the gas in its outer layers. Those layers expand and get cooler, causing Antares to shine with a definite orange or reddish glow. The puffed-up outer layers make Antares truly enormous. While it's about 15 to 20 times heavier than the Sun, it's several hundred times wider -- a diameter of several hundred million miles. If it took the Sun's place in the solar system, it would engulf the four innermost planets, and extend most of the way out to the orbit of the next planet, Jupiter. Or to put it another way, if Earth were the size of a marble, Antares would be as big as Disneyland.