In A Nutshell
Right now, Polaris is the North Star, but it’s technically not the only one. Recent technology has allowed us to finally get a glimpse at Polaris’s companion stars. While one can be seen with a regular telescope, another is so close that the Hubble only got a picture of it in 2006. There are technically more “North Stars” than Polaris, too. Around 5,000 years ago, the pole star was Thuban, now a star in the constellation Draco. Next, it’ll be Errai, and after that, it’ll be Alderamin. The constant change is due to the slightly unsteady rotation of Earth.
The Whole Bushel
Polaris is the North Star. We’re all familiar with the stories about how it’s helped people navigate at night for thousands of years, but those people who relied on it for centuries didn’t know anything about the other North Stars.
Polaris is a star, the same as our Sun is. But Polaris is a triple star system, with two other bodies held in orbit around it because of its massive gravitational pull. About four times the size of our Sun and around 2,000 times brighter, Polaris is so bright—and one of its companion stars is so close to it—that we’ve only recently been able to get a good look at it.
It was only in January 2006 that NASA was able to confirm they’d gotten the first pictures of Polaris’s companion star, and even then, it was stretching the technological capabilities of the Hubble telescope to their limit. They found that the companion is a dwarf star, and they’ve estimated it takes about 30 years for it to make one orbit around Polaris.
The discovery of the second star comes with some staggeringly huge numbers and some very tiny ones. Polaris is an estimated 430 light-years away, and its companion is about a couple billion miles away from it. As an earthly comparison, NASA says the little mini-Polaris looks the same as a quarter would look, when viewed from a distance of 30 kilometers (19 mi).
Needless to say, there’s not a whole lot that astronomers know about it yet, but they’re hoping that’s going to change. If they want it to change while Polaris is still the North Star, they’d better get going. We’ve already gone through one, and another isn’t too far away, in the grand scheme of things.
In an era marked most dramatically by the building of the pyramids, there was a different North Star: Thuban. Whatever the purpose of the tunnels inside the pyramids might be, the Great Pyramid of Giza was aligned to Thuban, not Polaris. And it’s possible that in its day, Thuban was even more accurate than Polaris is today; ancient texts describe it as exactly marking the north celestial pole in 2787 BC. In between Thuban and Polaris, there were some rather inexact contenders, including Kochab, one of the stars in the Little Dipper. Since its short stint as a pole star around 1100 BC, it’s been steadily moving away to where we see it today.
The closest Polaris (once known as Phoenice) will ever get to completely accurate is an angle of 27’09”, and that’ll be happening on March 24, 2100. After that, it’ll be getting less and less accurate, until it’s finally replaced.
Around AD 4000, a new star will take the honor: Errai (also called Gamma Cephei), a moderately bright star with its own planet. The star has long had a mythology of its own, as the point in the constellation Cepheus the King.
And in 7500, the title of North Star will be passed along again, to Alderamin.
Why the different pole stars? The shift in the North Star all happens because the tilt of the Earth’s axis isn’t steady, varying between 22 and 24 degrees over the course of 41,000 years. Whatever stars lie on the circular path above the north pole will eventually be pole stars, as long as the Earth is around long enough to keep pointing to them.