Jimmy Westlake: The Seven Sisters
January 20, 2010
High overhead as darkness falls on cold January evenings is a tiny cluster of stars that often is mistaken for the Little Dipper. Although it does have a dipper shape to it with a tiny little bowl and a tiny little handle, its real name is the Pleiades.
It is the 45th object in Messier's famous catalog (M45), is popularly known as the Seven Sisters and in Japan is called the Subaru. A likeness of the Pleiades star cluster adorns every Subaru car on the road.
A person with average vision should have no difficulty seeing six stars in the cluster, and a bit of careful searching should reveal the seventh faint star, as well. A person with exceptional eyesight might make out as many as 8, 9 or even 10 stars with their unaided eye. How many can you see?
The name "Seven Sisters" is actually a misnomer because only five of the seven naked-eye stars represent the mythological sisters. The other two stars represent the parents, Atlas, the father, and Pleione, the mother. In order of decreasing brightness, the seven brightest stars are named Alcyone, Atlas, Electra, Maia, Merope, Taygeta and Pleione. The other two sisters, at the edge of visibility, are Celaeno and Sterope. A simple pair of binoculars will clearly reveal the entire family and many dozens more stars to boot.
Mythology explains that the big brute Orion the Hunter, also seen in the winter stars, was chasing the beautiful daughters of Atlas and Pleione.
Zeus, the king of the Greek gods, heard their cries for help and transformed the maidens into white doves so that they could escape Orion's lustful pursuit. They flew high into the heavens and still are seen today as our Pleiades star cluster. The three stars of Orion's Belt point upward like an arrow toward the Seven Sisters.
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A more modern, scientific explanation for the lovely cluster of stars is that they were, indeed, all born as siblings from the same cloud of hydrogen gas only about 10 million years ago. There are more than 500 member stars in the Pleiades cluster, all lying about 410 light years away from our solar system. That means that when you look at the Pleiades star cluster, you are seeing it as it was 410 years ago.
Although the Pleiades stood alone as a separate constellation for many centuries, modern astronomers have included it within the boundaries of our constellation of Taurus the Bull. The tiny cluster lies on the bull's shoulder.
On Sunday evening, the waxing gibbous moon will appear very close to the Pleiades star cluster. Although the bright moonlight likely will drown out the fainter members of the Pleiades, you still should be able to spot the twinkly star cluster trailing just behind the moon.
Professor 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 around the world. His "Celestial News" column appears weekly in the Steamboat Pilot & Today. His "Cosmic Moment" radio spots can be heard on local radio station KFMU. Also, check out Jimmy's Web site here.