Moon and Antares

• ‹ Previous program
• 249 of 1968
• Next program ›

Our planet Earth is sometimes described as a "blue marble" -- a tiny ball of color and life in the cold, dark universe. But the description seems particularly apt when you consider one of the highlights of tonight's sky: the star Antares, which snuggles quite close to the Moon.

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.

Look for Antares just a mouse-whisker away from the Moon. It's above or to the upper left of the Moon at nightfall. At their closest, they'll be separated by little more than the width of the Moon itself. Depending on your location, they set by around 11 or 11:30.

Script by Damond Benningfield, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.