The constellation Hercules, the strongman, climbs into good view on May evenings. This view is about 90 minutes after sunset, looking east and northeast. The constellation's most prominent feature is the Keystone, while other features include two globular star clusters. [Tim Jones]
He's strong in legend and even stronger in the movies. But in the sky, Hercules is a bit of a weakling. Although his constellation is fairly large, none of its stars is among the hundred brightest in the sky, so you need fairly dark skies to see it.
The strongman's leading light is Kornephoros -- "the club bearer." It's near the right edge of the constellation as Hercules climbs into view.
Like many of the stars that are visible to the unaided eye, Kornephoros is a giant -- a star that's puffed up as it nears the end of its life. It's probably about 20 times wider than the Sun. At that diameter, it's big enough to hold about 8,000 Suns. With such a large surface area, it puts out quite a bit of light. So even though it doesn't look that impressive in our sky, the star is bright enough to see across about 150 light-years of space.
Kornephoros has puffed up because of changes in its core. It's used up its original hydrogen fuel, and is now burning the helium "ash" created in that process. When it consumes the helium, the star will get even bigger -- so big that if it took the Sun's place, it would engulf Earth. For a while, the star will shine far brighter, too -- making the strongman look a lot stronger.
Look for Hercules low across the east and northeast after it gets dark. Its most prominent feature is a lopsided "square" of stars known as the Keystone. Kornephoros is to the right of the Keystone.
More about another star in Hercules tomorrow.
Script by Damond Benningfield, Copyright 2010
For more skywatching tips, astronomy news, and much more, read StarDate magazine.