The Pole Star
I’ve been doing some informal polling during our daytime field trips to Perkins, and I’d like to share the results with you. Ask your average fifth grader to identify the brightest star, and most of them will reply, “Polaris,” the North Star.
A quick trip outside demonstrates that your average fifth grader is wrong. Polaris is the end star in the tail of Ursa Minor, the Little Bear, also known as the Little Dipper. Polaris is easy enough to find if you can see it at all. It is, after all the NORTH star. Just look directly north about half way up from the horizon. Sadly, Polaris is not particularly bright. It’s difficult to see from suburban skies because of all the streetlight pollution, and you won’t see it at all from downtown Columbus.
What makes Polaris special is that every other star you see changes its position over the course of a night. Polaris just seems to sit there. Of course, the stars are so far away that from the perspective of a fixed point in space, they don’t seem to be moving at all. We’re the ones who are moving. Earth rotates once every day. At 40 degrees latitude, where we’re located, we are hurtling around the spinning terrestrial orb at 680 miles per hour. And that would knock your hat right off if your hat weren’t also traveling at the same velocity.
In a sense, Polaris isn’t fixed at all. Where it is in the sky depends on where you happening to be standing on Earth, as early sailors trying to find there way around soon learned. To the south of Earth’s equator, the North Star is invisible below the northern horizon. Directly above the equator, the Pole Star sits just above the northern horizon.
At 40 degrees latitude, it hovers 40 degrees above the horizon, about half way from the horizon to the top of the sky. At 20 degrees latitude, Polaris is 20 degrees above the horizon, and so on.
Since Earth is spinning from west to east, the sun, moon, planets, and most of the stars seem to move from east to west.
From our Delaware vantage, they circle around Polaris, rising above the horizon and eventually setting.
The oddest place to observe Polaris would be from the North Pole. If you were standing right next to Santa’s workshop, Polaris would be straight overhead, and the other stars would spin around it like horses on a merry-go-round. That’s something I’ve always wanted to do. I have a bone to pick with Santa about that telescope I didn’t get when I was eight years old.
Another way of thinking about Polaris is that it is directly above the imaginary line that passes through Earth’s north and south poles. Extend that line 820 light years (or 5 quadrillion miles) into space and you’ll run into the Pole Star. Well, almost, anyway. Polaris isn’t directly north. It actually scribes a circle, albeit a small one, over the course of a day and night, just like all the other stars.
And there’s another problem. Earth wobbles a little as it spins on its axis. Over the course of 26,000 years, the position of the pole in the sky changes. Right now, it’s near Polaris. To the ancient Egyptians in 3,000 BCE, the North Star was the star Thuban in the constellation Draco, the Dragon. Our cave-dwelling ancestors 18,000 years ago looked toward Alderamin, the brightest star in Cepheus, when they wanted to find their way.
The pole will never be pointed directly at Polaris, but it reached its closest point in 2005. Every second that passes, the pole moves a bit farther away from Polaris and toward the star Vega in the constellation Lyra. In 50,000 years or so Vega will be the closest star to the pole. Don’t forget to mark it on your calendar.
Astronomy Fair
Starting at 4 p.m. This Saturday, Sept. 10, the Columbus Astronomical Society will hold its annual Astronomy Fair at Perkins Observatory. They’re charging $5 per car admission and will donate the proceeds to Perkins Observatory. If you want to get a great introduction to stargazing and a daytime tour of the observatory as well come on down.
Tom Burns is the director of Ohio Wesleyan University’s Perkins Observatory. Contact him at tlburns@owu.edu.
