Look up into the north one of these pleasant spring evenings and see if you can spot the Big Dipper riding high in the sky. Follow the arc of the Dipper’s handle to a bright orange-colored star in the east. That is Arcturus, one of the brightest stars in the sky and a close neighbor of our sun.
Notice that its name sounds a little bit like our word arctic. That is because they both come from the same Greek root word, arktos, which means bear. Our word arctic means realm of the bears and Arcturus means guardian of the bears. Arcturus was supposed to keep the two bears, which we call the Big and Little Dippers, in their orbit around the North Star.
Look for a kite-shaped pattern of dimmer stars above Arcturus. That is the rest of the constellation of Bootes, the herdsman. Bootes’ claim to fame was his invention of an amazing high-tech device which radically changed the lives of ancient people, the plow. Because of his invention the gods thought he deserved to be placed in the stars along with the other great heroes. Wait a minute. He invented the plow? How hard could that be? What about the guy who invented the iPhone? Why isn’t he up there?
When we look up at Arcturus we are actually looking into our future. Arcturus is several billion years older than our sun and what we see up there is what we will get in our deep future. Arcturus is the same weight as our sun and quite a bit bigger. Also, it pumps out about 180 times the energy as our sun. That means it is hot, way too hot. This will happen to us too about a billion years from now, and we will have to move to someplace cooler like one of the moons of Jupiter perhaps. That is if anyone survives global warming, many ice ages and whatever else the universe throws at us.
Not alone up there
Another interesting thing about Arcturus is that it is not traveling alone through the cosmos. It has a group of friends along with it that astronomers have been observing for the last 50 years. They call it the Arcturus moving stream of stars. Arcturus is the only one we can see with the naked eye because it happens to be quite close to us, relatively speaking of course. The question comes up, are these stars locals or are they from out-of-town on a road trip?
Here are the facts. All of these stars are the same age, they are all going the same speed, they are all headed in the same direction and they are all in a completely different orbit around our Milky Way galaxy than our sun and the 300 billion other stars sharing our home with us.
Some astronomers think that Arcturus and his pals were actually born in another galaxy altogether, a small dwarf galaxy that fell into the Milky Way five billion years ago about the time that our sun was born. Thus the road trip theory. The little galaxy was completely shredded, but the stars themselves survived and are now incorporated into our galaxy. It is called galactic cannibalism, and it will happen to us someday when we are devoured by the much larger Andromeda galaxy. That is another story which I have told before.
Other astronomers have examined the composition of the companions of Arcturus and found that they are just like the stars born and raised right here in the good old Milky Way. So maybe they are locals after all. Astronomers are still scratching their heads over that one, and if they ever figure it out, I will let you know.
The planets are mostly hanging out in the east just before dawn. On April 30, Jupiter and Venus will make a close and spectacular pass definitely worth watching, but you will have to get up early. In mid-April, see if you can spot the planet Mercury low in the west above where the sun went down. At least you do not have to set the alarm clock for that one.
One more thing about Arcturus. If you want to see it do not put it off too long. It is zooming off in another direction and in 100,000 years or so will be out of sight for good.