Before you climb a ladder, you want to make sure all of its rungs are secure. And astronomers try to do the same thing – with the cosmic distance ladder. It’s a series of techniques that reveal the distances to objects that are farther and farther away. For it to work, all the rungs have to be secure.

One of the first rungs on the ladder uses a class of stars called Cepheid variables – big stars that are nearing the end of life. They’re unstable, so they pulse in and out. The length of the pulses and other details reveal a Cepheid’s true brightness. From that, you can calculate the star’s distance.

For this step to work, astronomers need to know all they can about Cepheids. But that’s not easy. In fact, they’re still debating the details on the closest and most famous Cepheid: Polaris, the pole star, which stands due north.

We do know that Polaris consists of at least three stars. The Cepheid is the one that we see with our eyes alone. It has a close companion. The third member of the system is quite a ways from the other two.

The system appears to be about 450 light-years away. And a recent study says the Cepheid is about five times the mass of the Sun. Its surface has some big dark and bright spots. Their motion suggests the star rotates once every four months.

Even those details aren’t certain. So astronomers still have to do a lot of checking to make sure one of the rungs of the cosmic ladder is secure.

Script by Damond Benningfield