Scientists Don't Know Why Polaris Is So Weird

For as long we we leaned on it to guide us, we know surprisingly little about the North Star. Nick Smart/Shutterstock

Humans have long relied on the starry sky to push into new frontiers, sail to the very edge of the world and find their way back home again. Even animals look to the stars to guide them on their epic migrations.

It's hard to be truly lost when you've got celestial signposts like Vega, Sirius and Acturis to light your way. Unless, of course, it's cloudy outside. Or worse, one of those guides starts acting a little wonky.

Such appears to be the case with one of our most reliable guides: Polaris, better known as the North Star.

As a navigational tool, Polaris has a lot going for it: It's a cepheid, meaning it holds to a very regular pulse, never changing in diameter or brightness. Most importantly, it glimmers almost directly over our North Pole. As long as you can see the sky, you can see your way north.

(Just look for the Big Dipper and you'll zero in on Polaris in no time.)

But scientists are beginning to question the very nature of this most venerable guide. According to new research, the star's distance from Earth is fluctuating. They also confirm that no one's quite sure about its mass.

Polaris seems to be our friend simply by virtue of being there for us when we look up at the sky.

"However, as we learn more, it is becoming clear that we understand less," the authors note, rather un-reassuringly, in the paper.

One of the most common ways to measure a star's distance from us is called the stellar evolution model. It starts with careful measurements of a body's brightness, color and frequency of pulse to determine its size and age.

And then, as study co-author and University of Toronto astrophysicist Hilding R. Neilson tells Live Science, working out its distance is pretty straightforward. In that sense, cepheids like Polaris should also make great guides to cosmic cartographers too: They help astronomers calculate distances across the vastness of space.

But Polaris may not be so into that career path. It seems to be thwarting our efforts to nail down its mass.

Measurements using the stellar evolution model, for instance, don't jibe with those used for the recent study. The former pegs Polaris at 7.5 solar masses. While the new research suggests it's closer to 3.45 times the mass of the sun. That's a wide discrepancy, making it even harder to pin down the star's distance from us, which has long been held to be around 430 light-years.

A map of the night sky showing the Big Dipper and the North Star.
It may not be the brightest star, but Polaris is pretty easy to spot. Vector FX/Shutterstock

As David Turner, an astronomer at St. Mary's University in Halifax, Canada who didn't work on the new study points out, "There are many mysteries about Polaris that defy simple explanation. I think I will sit on the fence in this case and await further observational results."

And we may have to keep that fence warm a little longer, as we still struggle to understand the enigmatic star.

In the meantime, here are a few astonishing things we know for sure about about our brilliant friend:

Starlight, star not-so-bright...

Polaris isn't as brilliant as its reputation would suggest. It actually ranks 50th among bright and shiny celestial objects. Even Betelgeuse, which is dimming rapidly, still holds down the #21 spot. And if you really want bright, look to the top "dog." That would, literally, be the "Dog Star" Sirius.

But it still blinds scientists.

No, it doesn't exactly take center stage, as it dances among the stars. But Polaris is actually incredibly bright — so bright that it makes studying it very difficult. As Neilson points out in Live Science, the discrepancy in measurements may suggest that one model is flat-out wrong. And that may be because the North Star not only eludes many a telescope's field of view — being above the North Pole and all. It also overwhelms the equipment designed to study the properties of stars. As seen through a telescope, it's basically celestial liquid paper.

Polaris has an older friend.

It may seem like a solitary gleam from some deep, dark pocket of space, but Polaris is hardly alone. Look closely at the star, even from Earth, and you may make out its companion, a much dimmer bulb with an appropriately dimmer name: Polaris B. That little bauble twirls around

"Polaris is what we call an astrometric binary," Neilson notes, "which means you can actually see its companion going around it, sort of like a circle being drawn around Polaris. And that takes about 26 years."

Even stranger? According to the new study, that friend is older than the main star it orbits. The researchers suggest this strange arrangement may be the result of another star smashing into Polaris — which may have drawn in extra material and given both stars a new lease on life.

It didn't always hold down a gig as the North Star.

While Polaris is certainly older than our planet, it only recently started its job as a signpost to the North.

A phenomenon known as "recession" means stars are constantly changing their position relative to us.

So, back in 3,000 BC, a star called Thuban held the job. There's a good chance it even helped ancient builders nail those perfect angles on the Egyptian pyramids.

At the time. Polaris was still pretty close to the North Pole — possibly even interning for the job. But Thuban didn't move on to other opportunities until around the 6th century.

And if humans happen to be around in the year 3000, they may congratulate a star named Gamma Cephei on its first day on the job.

They may also bid a fond farewell to weird Polaris, giving thanks for all the great work it did.