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North vs. South

StarDate: 
September 20, 2015

From the latitudes of the United States, there’s a big difference between the northern half of the night sky and the southern half. The northern half basically displays the same constellations every night of the year. Their positions change, but it’s still the same star patterns. But the southern half shows different constellations as the nights roll by.

It’s all caused by Earth’s rotation. Our planet’s axis points toward Polaris, which is also known as the North Star or the Pole Star. As Earth turns, Polaris remains in the same position in the sky, and the other stars all rotate around it.

To envision how that provides different perspectives on the stars, imagine that Polaris is the top of a pole at the center of a circus tent, with colorful stripes radiating away from it. If you look straight up, then spin around, you’ll see the same stripes all the time — just in different positions. But if you look out toward the bleachers, you’ll see different parts of the bleachers as you turn.

And that’s what happens in the sky. The stars that are close to Polaris trace little circles around the Pole Star. These stars never set.

As you look farther from the Pole Star, though, the stars begin to dip below the horizon. And as you look toward the southern sky, the stars remain below the horizon for many hours at a time. That means that they’re in good view at certain seasons of the year, but not at others — different perspectives on the night sky.

 

Script by Damond Benningfield, Copyright 2015

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