Naked-eye astronomy


by Chris Holmes

Using the Big Dipper to find Polaris in the northern sky.

This article is the second in a series highlighting the wonders that lie right above us in the Hidden Meadows sky every night.

“Let us go then, you and I,

When the evening is laid out against the sky,

Like a patient etherized upon a table.”

(T.S. Eliot, “Love Song of J. Alfred Prufrock”)

“Dad, Dad…can I get a telescope?” begged the young boy as he and his father looked up at the stars.

“Maybe someday,” answered the father with a laugh.  “But did you know that on a dark night we can actually see over 1000 stars just with our naked eyes?  Here in Hidden Meadows, the we don’t have a lot of street lights and the sky is darker, so it’s even easier to see them.”

“Look, look, Dad!  I see the Big Dipper!  It looks like a big spoon with a long handle!”

“Good job, son. That group of stars is also know as The Drinking Gourd, and it’s part of a constellation in the northern sky called Ursa Major or the Big Bear.  Did you know that you could use it to help find your way?”

“How, Dad?”

“Well, imagine you’re in a boat lost at sea, without a compass or charts.  You have a paddle but don’t know which way to go.  If you look up at the Big Dipper and draw a line extending out from the two outermost stars on the bowl of the spoon, they’ll point you to Polaris. Here, I’ll draw you a picture…

“Navigators use Polaris as their “pole star,” continued the dad. “It’s called that because it sits directly above the North Pole.  Finding it in the sky would tell you where true North is and make it easier to know which way to steer your boat.  During the Civil War, Polaris supposedly helped runaway slaves find their way  up north to freedom.  There’s an old folk song about that called “Follow the Drinking Gourd.”

“Okay, but how would that work, Dad?  Don’t the positions of the stars change during the night?”

“You’re right, the stars appear to move westward at night because the Earth is rotating.  But Polaris is in line with the Earth’s axis of rotation, so it stays in place, right above the North Pole.  If we brought out our camera and took a time-lapsed picture of it, even just for an hour, we’d see it there in the middle, with a circular pattern of other stars moving around it.  Pretty cool, huh?”

“So can everyone in the world see Polaris in exactly the same place?”

“Well, it depends on what latitude you’re at.  Here in Escondido we’re at 33 degrees North Latitude.  So if we look at the horizon and tilt our chin up 33 degrees, that’s the altitude where we’d find Polaris.  If we were at the North Pole, it would be directly overhead. Down in the Southern Hemisphere we wouldn’t be able to see it at all.”

“If you want to get really scientific, Son, the star we call Polaris hasn’t always been the pole star.  That’s because the Earth wobbles ever so slightly as it spins around — a process called precession.  As a result, the star closest to the Earth’s axis changes over time.  In fact, 3300 years ago, when Moses looked up and prayed to the heavens, the pole star was a star called Thuban, in the constellation Draco. A few thousand years from now, Polaris won’t be known as the pole star, some other star will be.”

“I don’t think I’ll be around in a thousand years to worry about the pole star,” mused the boy.

“Probably not, Son.  But if you’re around tomorrow night, we can do some more stargazing.  You’ll be happy to hear that astronomers have identified 88 different constellations that are visible without a telescope.  Next time, we’ll use the other end of the Big Dipper — the handle — as a pointer to an interesting group of stars called the Summer Triangle.”

“I can’t wait!!”