Jimmy Westlake: Tale of 2 clusters
November 20, 2012
Stars are born in clusters — families of dozens to hundreds of stars that share the same age and chemical makeup — but they don't remain in clusters their whole lives. Like fledgling birds, stars eventually leave the nest in which they were born to roam the galaxy alone.
There are hundreds of star clusters that populate our Milky Way galaxy, many of which are visible from Earth to unaided human eyes. Most appear as faint, fuzzy smudges in the night sky because of their great distance from us, but there are two clusters close enough to allow us to see their brightest members as individual suns.
On cold, crisp November evenings, you can spot these two magnificent star clusters in our constellation of Taurus the Bull. They are the Hyades (high-a-deez) and the Pleiades (plee-a-deez) star clusters. The Hyades cluster forms the familiar V-shaped face of Taurus, with the bright orange star Aldebaran as one of his glaring red eyes. Aldebaran itself is not a member of the Hyades but is superimposed on the cluster as a foreground star, only half as far away. At a distance of 153 light years, the Hyades cluster is the closest star cluster to our solar system.
Leading the Hyades westward across the sky is Taurus' second star cluster, the Pleiades, marking the Bull's shoulder. Also known as the Seven Sisters, the Pleiades star cluster lies nearly twice as far from us as the Hyades cluster, so it appears much smaller in size, but its importance to the sky-watchers of the past cannot be overstated. The star Aldebaran received its name from the Arabic words that mean "The Follower" because it rises just behind the Pleiades and obediently follows them across the heavens.
The Hyades and Pleiades star clusters are steeped in ancient legend and have been pondered and ogled by curious eyes since antiquity. Here's a sample of the star lore surrounding these two clusters.
Hyas was the son of a Titan named Atlas. His seven half-sisters by a different mother were the Hyades, a name that means "the rainy ones." Hyas grew into a renowned archer and hunter but one day wound up being killed by his prey — a wild boar. His sisters were so overcome with grief that they wept themselves to death. Zeus, the king of the Greek gods, immortalized the sisters by placing them among the stars as the Hyades star cluster. During the rainy season of April and May, the Hyades are not seen because they are too close to the sun in our daytime sky. The Greeks considered the springtime rains as the never-ending tears of the Hyades, grieving for their fallen brother.
The Pleiades were the seven half-sisters of the Hyades by yet a different mother. After Atlas and the Titans were defeated by Zeus and the Olympians in the great war for control of the universe, Atlas' punishment was to toil for eternity, holding up the sky. Unable to look after his daughters, Atlas had to watch helplessly as the brute Orion relentlessly pursued the seven beautiful Pleiades. Zeus took pity on them and first changed them into doves so that they might escape Orion's advances before finally changing them into the seven twinkling stars of the Pleiades star cluster, just out of Orion's reach. He placed them in the heavens beside their grieving half-sisters, the Hyades.
Look for the Hyades and Pleiades star clusters high in the eastern sky at about 9 p.m. in late November. The three stars of Orion's Belt point upward to them like an arrow. The dazzling planet Jupiter shines nearby both clusters this fall and winter. Aim your binoculars at the clusters to see dozens of fainter stars.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. Check out Westlake's astrophotography website at http://www.jwestlake.com.