As seen from most of the United States, the Big Dipper is plunging toward the northern horizon as night falls, as if it’s about to dip into a pail of water.

If you line up the stars at the outer edge of the dipper’s bowl, and follow that line to the upper right, the first moderately bright star you come to is Polaris, the Pole Star or North Star. Earth’s north pole aims toward it, so Polaris forms the hub of the northern sky – all the other stars appear to rotate around it. And it’s always at the same point above the horizon – night and day, all year long.

There’s a southern pole star, too. It’s not as prominent as Polaris, though. In fact, it’s barely visible.

The star is Polaris Australis. It’s also known as Sigma Octantis because it’s in the constellation Octans, which depicts a navigational instrument known as an octant.

Polaris Australis isn’t as impressive as Polaris mainly because Polaris is huge and brilliant.

Compared to most stars, though, the southern pole star is impressive, too. It’s more than half again the mass of the Sun. It’s expanding as it nears the end of its life, so it’s several times wider than the Sun. And its outer layers puff in and out, so it brightens and fades a tiny bit every couple of hours. On average,

it’s more than 40 times brighter than the Sun. But it’s almost 300 light-years away. So that keeps Polaris Australis from being a better pointer to the celestial south pole.

Script by Damond Benningfield