BY MIKE LYNCH
I don’t know about you, but with what’s been going on in our world we’ll take every bit of good news that we can. Well, we have some.
It is officially summer. The sun is in its most northern position of the year. Because of that, the sun will take its highest and longest arc across the sky. We won’t talk about days getting shorter after this weekend though.
Without a doubt, the brightest star in the Pottsville summer night sky is Arcturus. It’s actually been visible in the evening sky since February when it was barely above the horizon in the early evening. I love it when Arcturus starts to appear because it’s a promise that summer’s on the way. Once again, the promise has been kept.
Earth has moved far enough in its orbit around the sun to give us a more direct view of Arcturus. That’s why it’s so much higher in the evening sky. As twilight fades, Arcturus pops into view very high in the southern sky. You can’t miss it. It’s the brightest star in the sky!
If you want even more confirmation you’re seeing Arcturus, just use the old reliable stargazing tool, “Arc to Arcturus.” Find the arc of the handle of the Big Dipper, and with your mind’s eye extend that arc beyond the end of the Dipper’s handle. You’ll run right into Arcturus, guaranteed!
Not only is Arcturus the brightest star in the summer night sky, it’s also the brightest star in the constellation Bootes the Farmer, or Herdsman. Rather than a hunter, though, Bootes looks much more like a giant kite with Arturus beaming at the tail.
You also can’t help but notice that Arcturus has an orange-reddish glow. It’s considered by astronomers to be a red giant star, way more extensive than our own sun with a diameter of 22 million miles.
Our sun isn’t even a million miles across! Arcturus is 37 light-years from Earth, with just one light-year equaling nearly 6 trillion miles. It’s so far away that the light we see from it now left that star shortly after Ronald Reagan became the United States president.
The really cool thing about the night sky is that when we look up at the constellations we essentially see the same star patterns that our ancestors saw thousands of years ago. They’re also the same patterns our descendants will see thousands of years from now. Stars are often referred to as fixed, but very strictly speaking they’re not. They’re constantly on the move, tearing along at incredible speeds. Most of them, like our sun, are obediently orbiting around the center of our Milky Way galaxy. There are some mavericks that travel in all different directions. We can’t easily detect the changing positions of the stars among each other because of their incredible distances. That’s why they seem fixed in place.
There are some exceptions, though, and Arcturus is one of them. About 300 years ago, Sir Edmund Halley, the same guy who the famous comet is named after, detected changes in Arcturus’ position relative to nearby stars in the sky by comparing ancient star charts with what he was observing at the time.
Since then, it’s been determined that Arcturus is moving more than 75 miles a second relative to our solar system. And, it’s coming in our direction! Many astronomers believe that it’s about as close to us as it’s going to be. Turning the clock backward as little as a half a million years ago, it’s believed that Arcturus was so far away that it wasn’t even visible to the naked eye. And, in about another half million years, it will fade from our view, never to be seen again.
Don’t take summer for granted, and don’t take the brightest star of summer for granted either, although it still has quite a few summers to go!
Lynch, an amateur astronomer and professional broadcast meteorologist, can be reached at firstname.lastname@example.org.