This Month's Star

This month look for the star Alcyone, the brightest star in the open cluster, the Pleiades. To the Japanese, the cluster is known as Subaru. If you look at the emblem on the same car you’ll see the Pleiades. The Pleiades goes by the name of M-45 and is also known as the Seven Sisters. Most people only see six stars in the Pleiades. The seven sisters were daughters of the titan, Atlas and his wife, Pleione. The six stars most people see, in order of brightness, are named, Alcyone, Electra, Maia, Atlas, Merope, and Taygeta. The next three fainter stars are named after the their mother and the two remaining sisters, Pleione, Celaeno, and Asterope   The first known mention of the Pleiades is by the writer Hesiod around 1000 BC.  

In 10X50 binoculars, the brightest portion of the Pleiades occupies about 1/5th of the field of view. When you include the fainter surrounding stars, the Pleiades occupies closer to 1/4th of the field of view. In moderately light polluted skies, I could easily see 20 stars. In the diagram above, Alcyone, the brightest Pleiad, is the star in the center.

The Pleiades are 369 light years away. So the light you see tonight left the star cluster in the year 1645. There are some 500 stars in this galactic cluster. They formed from the same cloud of dust and gas about 100 million years ago. This means they were born during the middle of the Cretaceous period, or during the hey-day of the dinosaurs. In time the stars of this cluster will drift a part, as their gravity is too weak to hold the cluster together. In other words, there are too few stars spread too far a part. In long duration exposures a blue cloud of dust can be seen surrounding the stars. The stars and bright blue-white frosting makes the Pleiades look like some fantastic piece of jewelry. Contrary to popular belief, this is not the remains of the cloud that the Pleiades formed from. It happens to be a separate cloud that the cluster is currently drifting through. Recent findings have determined that the cloud of dust is actually two separate clouds that are passing each other just as the Pleiades are passing through the same area.