By David Ward
The seasons are changing and we can see it all around us. The trees are now bare of their leaves, and snow blankets the mountains. If you know the stars and understand their motion, you can see that change in the night sky also.
In the west, just after dark, the Summer Triangle — with its three stars Vega, Deneb and Altair — is getting lower and lower. Soon it will be out of sight altogether, returning in late spring.
In the east, the beautiful and bright stars of winter are just making their appearance. Just after it gets dark, look in that direction for a little cluster of dimmer stars about the size of the full moon. There is nothing else in the sky quite like it, so once you spot it, it is unmistakable.
The English poet Tennyson spoke of them as “glittering like a swarm of fire flies tangled in a silver braid.” In more modern times you can see this very same cluster of stars adorning the hoods of a certain make of Japanese automobile. They were important to the people who lived on the shores of the Mediterranean Sea in ancient times. Their appearance in the east in the fall marked the time of year when it was wise to put away your boat for the winter rather than risk your life sailing around on a stormy sea.
I am talking about the Pleiades star cluster, of course, the famous and beautiful Seven Sisters of ancient Greece. They were the daughters of the titan god Atlas and Pleione, a nymph from Mount Kyllene in Southern Greece.
The sisters were companions of the goddess Artemis and the would-be girlfriends of Orion, the boastful hunter. One day Orion caught a glimpse of them in the forest and fell in love at first sight. He chased the beautiful sisters for seven years but they spurned his amorous advances. Finally Zeus, king of the gods, took pity on the maidens and turned them first into doves and then into stars in the sky.
Orion was placed in the stars also, one of the brightest and best-known constellations up there. He rises later in the evening than the Pleiades, and if you stay out and watch, he chases them across the sky each winter night.
Astronomically speaking, the star cluster is composed of blue, hot, extremely luminous stars about 444 light years away. To put that in perspective, that is about 18 times as far away as Vega, the brightest star in the Summer Triangle. The cluster was born in a cloud of gas about 75 million to 150 million years ago. Astronomers predict that it will only survive another 250 million years before the gargantuan gravitational forces of the Milky Way Galaxy tear the cluster apart and scatter the sisters across the sky.
Finding the sisters
How many sisters can you see with your eyes alone? If you have good vision, you should be able to see six. What happened to the seventh? The Greeks had a couple of stories for that. One was that the sister Merope hid her face in shame because she alone demeaned herself by marrying a mere mortal man. Another story tells us that sister Elektra left her other sisters and her starry post when the Greeks burned the city of Troy, founded by her son Dardanus. Try looking at them with binoculars. Many more will pop into view and they will truly “ glitter like fireflies.”
Just east of the Pleiades a bright reddish star named Aldebaran, also known as the “follower,” is poking up over the horizon. What is it following? The Pleiades, of course. Everybody loved those beautiful Seven Sisters. Aldebaran also lives a double life as the angry red eye of Taurus the bull.
Look for a “V” of dimmer stars extending to the right of Aldebaran. This is the Hyades star cluster, the closest tight grouping of stars to Earth, about one-third of the distance to the Pleiades. They were known to the ancient Greeks as the “rainy ones” since their appearance heralded the start of the fall rains. These stars were sisters also. Generally, five of them were identified, and they were half-sisters of the Pleiades, but not nearly so famous.
There are no visible naked-eye planets in the evening sky this month, so if you want to see any, get up early, about an hour before sunrise. Look in the east for two very bright lights in the sky. The upper one is Jupiter and the even more-brilliant Venus is lower. If the sky is still mostly dark, you should be able to spot much-dimmer Mars in line with the other two.
If we could get in a time machine and fast -forward ourselves 10,000 years into the future, the night sky would look almost exactly the same as it does now. The stars would not have changed their positions in relation to one another. All the stars are moving at high rates of speed in their grand dance through the Milky Way Galaxy.
Our sun, pulling Earth and the other planets along with it, is cruising along at 500,000 miles per hour. The distances are so vast and our lives so short that we do not notice their movement during that extremely brief moment that we inhabit this little planet. The Pleiades are actually moving across the sky back to Orion. He will have to be a patient suitor, though, as it will take tens of millions of years before he will finally be able to catch them.