Jimmy Westlake: Two giants of summer
July 28, 2014
Steamboat Springs — Two giant 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 shown standing on top of the constellation Scorpius as a symbol of his power over it. The bright bluish-white star named 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, 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 straight up overhead and just west of the very bright blue star Vega in the early evening.
If you own a pair of binoculars or a small telescope, you can spot what looks like a small, fuzzy dandelion head along the western side of the Keystone. This fuzz ball 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.
From nearly 25,000 light years away, M13's one million stars appear to us as that fuzz ball 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 that you can see without a telescope.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Check out Jimmy's astrophotography website at http://www.jwestlake.com.