Draco

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Our perspective on the night sky changes hour by hour. That's because Earth is spinning on its axis, so as the hours pass we face different sections of the sky.

But this spinning also causes our perspective to change century by century. As Earth spins, it wobbles like a toy gyroscope. Earth's wobble is caused by the gravitational pull of the Sun and Moon. It takes 26,000 years to complete one wobble. During that time, the planet's axis aims at different points in the sky. That means that we have different "north stars" at different times.

Today, the North Star is Polaris. But around 5,000 years ago, the pole took aim at a different star: Thuban, in the constellation Draco, the dragon.

Draco's an ancient constellation that twists through the northern sky. Its brightest star is Eltanin, an Arabic name that means "the serpent." It's in Draco's head.

Thuban is far down the dragon's body, and it's only about a quarter as bright as Eltanin. But because of its role as the North Star, it has a far brighter history. The star played a role in the layout of the pyramids of Giza. In fact, a shaft in the Great Pyramid of Khufu took dead aim at Thuban -- the hub of the night sky.

Look for Draco high in the north at nightfall. Eltanin is just to the north of the brilliant star Vega, which is high overhead. The dragon's body serpentines its way toward the northern horizon -- through Thuban, and around Polaris, its successor as the North Star.

Script by Damond Benningfield, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.