By David Ward
Everyone’s favorite little star cluster, the Pleiades, adorns our evening skies this month. Look up into the east just after it gets completely dark for a small grouping of dim stars about the size of the full moon. There is nothing up there anywhere quite like it. Some people mistake it for the Little Dipper because it has a dipper shape. The real Little Dipper is much larger, in the north, and much harder to see.
The strange name of the cluster, which is always hard for me to remember how to spell, comes from the Greek word meaning “to sail.” When the cluster was sighted in the east rising just before dawn, it meant that winter was over and it was safe to get out your boat and go for a jaunt on the Mediterranean Sea. The famous Greek king Odysseus sailing home from the Trojan War finally found his way after wandering lost for 10 years by steering his ship keeping the Pleiades on his starboard bow.
The Pleiades is one of the closest star clusters to us at 443 light years away. The fastest rocket that our technology can come up with would take over eight million years to get there. The cluster is 13 light years across, about three times the distance between us and the nearest star.
These are new stars, only about 100 million years old, and many shine hundreds of times brighter than our sun. Our sun was born in a cluster of stars like this five billion years ago, but the enormous gravitational forces of our galaxy have ripped us apart from our siblings. Now we journey through the vast cosmos as a lonely single star. About 250 million years from now, the Pleiades will start to break up, going their separate ways through space.
The Pleiades are also known as the beautiful seven sisters of ancient Greece. The great hunter Orion was madly in love with them and chased them around Greece for seven years. They spurned his amorous advances and pleaded to Zeus, king of the Gods, for help. He turned them into pigeons and then into the beautiful star cluster we see in the heavens today. Orion still chases them across the sky from east to west each night but he never catches them.
How many stars in the cluster can you see? Most people with good eyesight can spot only six. What happened to the seventh sister? The ancient Greeks had a legend for that. They claimed that sister Electra, mother of Dardanus, founder of Troy, hid her face in shame when the Greeks sacked and burned the ancient city on the Aegean Sea. Astronomers today have identified one of the stars of the cluster to be a complicated “shell star” which sometimes changes in brightness, which perhaps is the real answer to the missing sister.
The Pleiades will be visible all winter and best appreciated on a clear, dark, moonless night away from distracting lights. If you have a pair of binoculars, they will reveal many more fainter stars in the cluster.
That really bright object in the western twilight sky is the planet Venus. She will be gracing our evening skies all winter and getting higher and easier to see as December progresses. The first half of December is a great time to spot the planet Mercury. Look for him below and to the right of Venus. The innermost planet reaches its highest and easiest to see point on Dec. 10. You will have to look for it in the western twilight before it gets completely dark. Mars has been racing eastward away from the twilight glare and is now easier to see. Look for him to the left of Venus, a not-so-conspicuous reddish dot. If you are up before sunrise, that bright object high in the east is the planet Jupiter. Almost as bright as Venus, he is her brilliant counterpart in the eastern sky.
In case you missed it, we were buzzed by a space rock a couple of weeks ago. This thing was about 20 yards in diameter and came almost as close to us as our moon. It was discovered three days in advance by the Intruder Alert System, a new project that warns us of incoming objects of mass destruction. Is three days notice time enough for us to do something about it? Not really. If something that size did hit Earth, it would not wipe out humanity or anything like that, but local damage would be catastrophic. Imagine getting hit on the head by a rock weighing thousands of tons and going much faster than a bullet!
Everything up there is moving at speeds far faster than we can imagine. Our sun is cruising through the galaxy, pulling Earth and the other planets along with it at 500,000 miles per hour. The distances are so vast and our lives so short that we just do not notice. The Pleiades are moving too, and guess what? They are actually headed back to Orion! Millions of years from now they will be at his feet and he will have to chase them no more.