Jimmy Westlake: The giants of summer
August 20, 2012
Two very large constellations, Ophiuchus the Serpent Bearer and Hercules the Strong Man, take up a large chunk of our late-summer sky. We see them standing head to head, high up in the southern sky as darkness falls.
Ophiuchus represents Asclepius, the great witch doctor from Greek mythology. Asclepius is pictured in the sky grasping the large serpent that gave him the secret of restoring life to the dead. The serpent itself is actually a separate constellation named Serpens. Asclepius used his magic powers to resurrect Orion the Hunter after he received a fatal sting from a scorpion, so Asclepius is seen standing on top of the constellation Scorpius as a symbol of his power over it. The bright bluish-white star Rasalhague, meaning "the head of the snake charmer," marks Asclepius' head. Rasalhague (pronounced ras-al-hay'-gwee) adorns the top of a house-shaped asterism that forms the constellation of Ophiuchus.
The bright red star just to the west of Rasalhague has a similar sounding name and marks the head of another summer giant, Hercules, the famed son of Zeus in Greek mythology. This star is named Rasalgethi, meaning "the head of the kneeler." Rasalgethi (pronounced ras-al-geth'-ee) is a remarkable star. It is one of the reddest stars visible to the unaided eye, and with its faint emerald green companion star, it makes for a wondrous sight through a telescope. If Rasalgethi took the position of our sun in the middle of the solar system, its surface would extend out well beyond the orbit of the planet Mars.
Hercules is positioned upside down in our sky as the two giants of summer pose head to head. While Hercules contains no really bright stars, a prominent asterism called the "Keystone" makes locating the Strong Man fairly easy. Look for a quadrilateral made of four stars just west of the very bright blue star Vega, nearly overhead.
If you have a pair of binoculars or a small telescope, you should be able to spot what looks like a small, fuzzy dandelion head along the western side of the Keystone. This is the Great Hercules Star Cluster, also known by its catalog number M13. It is the finest example of a globular star cluster visible in the Northern Hemisphere. At a distance of nearly 25,000 light years, M13's 1 million stars appear to us as that fuzzy smudge you see in binoculars. On a clear, dark night, M13 can be glimpsed with the unaided eye, making it one of the most distant objects you can see without a telescope.
Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. He is an avid astronomer whose photographs and articles have been published across the world. Check out Westlake's astrophotography website at http://www.jwestlake.com.
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