During the week before Christmas, it seems fitting that we pay homage to a part of nature that, over the centuries, is often a traveler’s best friend: the guiding North Star. The timing is even more appropriate, since earlier this month, the National Geographic Society reported breaking news about our friend, Polaris.
It turns out that the North Star’s distance to Earth may have been grossly overestimated. Using a Russian six-meter telescope, researchers at Saint Mary’s University in Halifax, Nova Scotia, were able to calculate the North Star’s distance from our solar system by analyzing its light spectrum and obtaining data on its temperature and changes in brightness over time. They found the star to be about 323 light-years away — 30 percent closer to our solar system than previously thought. And since scientists use the North Star as a “cosmological yardstick” to measure great distances out to billions of light-years, it’s important for our understanding of the cosmos that we get a reliable grip on the North Star’s true distance.
But this news aside, there’s another facet to the North Star that might surprise you. Just as our understanding of the natural world changes with every new revelation, so does one of our most dearly depended-on guides: Polaris hasn’t always been the North Star — and it won’t remain the North Star forever.
Counting on our lucky stars
A 26,000-year precession cycle causes the north celestial pole (the point in the sky directly above Earth’s north rotational axis) to move counterclockwise relative to the backdrop stars. Whichever star is closest to the north celestial pole is the polestar. Five thousand years ago, when the Egyptians were building the pyramids, a star in the constellation Draco the Dragon, called Thuban, was the North Star — the point around which the heavens appeared to turn.
Some astronomers believe that Thuban made a better polestar than our modern Polaris since it almost exactly pinpointed the position of the north celestial pole in the year 2787 B.C., when it was less than 2.5 arc-minutes away from the pole. Our Polaris — which many centuries ago was an ordinary star known by the name Phoenice — won’t match Thuban’s precision when it most closely aligns with the north celestial pole on March 24, 2100. Polaris will be 30 arc-minutes, the diameter of the full moon, away from the north celestial pole at that time. It’s currently about 42.5 arc-minutes away.
But that doesn’t mean that our present Polaris isn’t a good North Star. It’s the fiftieth brightest star in the sky and therefore noticeable, even in some suburban skies. Spotting the North Star has brightened the prospects for many lost travelers. As you face Polaris and stretch your arms sideways, your right hand points due east, and your left hand points due west. About-face of Polaris steers you due south. At one time, people literally depended on the stars for their lives and livelihoods, trusting the North Star to guide them. Humans could sail the seas and cross trackless deserts without getting lost. Slaves in the United States once counted on the North Star to light their way to the free states and Canada.
Polaris will continue its reign until about 4000 A.D. The future North Star is likely to be Star Errai.
How to spot Polaris this Christmas
You can readily find the North Star by using the Big Dipper’s pointer stars, Dubhe and Merak, which outline the outer part of the Big Dipper’s bowl. Simply draw a line from Merak through Dubhe, and go about five times the Merak-Dubhe distance to Polaris.
We in the Northern Hemisphere are lucky when it comes to the stars. There is no visible star marking the celestial pole in the Southern Hemisphere. What’s more, the Southern Hemisphere won’t see a star appreciably close to the south celestial pole for another two thousand years.
Happy holidays — and best wishes for starry nights — to all of you nature enthusiasts, defenders, and champions.
Here’s to finding your true places and natural habitats,