The North Star is one of the most important beacons in the sky. It serves as a compass, pointing the way due north. And it also serves as the hub of the sky – all the other stars appear to circle around it as Earth turns on its axis.

More than 4,000 years ago, the architects of Egypt used the North Star to align the pyramids of Giza. And more than four decades ago, Apollo astronauts used it to help guide them to the Moon. But the two groups were aided by different north stars. The Egyptians used a star called Thuban, in Draco, the dragon. The astronauts used Polaris, at the end of the handle of the Little Dipper.

Thuban didn’t explode or fade away – it’s still in plain sight. Instead, Earth’s axis turned away from the star – an effect called precession.

It’s caused by the gravitational tug of the Sun and Moon, which cause our planet to wobble like a spinning top. As it wobbles, the axis points toward different stars. Four thousand years ago, it aimed at Thuban. Today, it aims at Polaris.

Over the next century, the pole will take slightly better aim at Polaris. Right now, the star is about two-thirds of a degree from where the axis is pointing. Around the year 2100, it’ll be less than half a degree from that spot.

After that, though, the pole will move away from Polaris. By around the year 4100, it’ll take aim at a star that’s one constellation over, in Cepheus – a North Star to guide future generations.

Script by Damond Benningfield