Welcome to brain Stuff production of I Heart Radio. Hey, brain Stuff, Lauren bog Obam here. If you ever looked at the night sky in the Northern Hemisphere, you've probably noticed a bright star that the rest of the heavens appears to move around. What you're seeing is Polaris, also known as the North Star, which is approximately four and thirty light years away from Earth and is part of
the constellation Ursa minor. The North Star is thus named because its location in the night sky is almost directly over the North Pole. We spoke via email with Rick Feinberg, a Harvard trained astronomer who is now Press Officer of the American Astronomical Society. He said, so, if you were to stand at the North Pole latitude ninety degrees north at night and look straight up, you'd see Polaris directly overhead.
From other latitudes in the Northern Hemisphere, if you face due north at night and look at the same angle above the horizon as your latitude, for example, look about half way up. That's forty five degrees. If you live in Portland, Oregon, at latitude forty five degrees north, you'll see Polaris shining there. Polaris is attention getting because unlike all the other stars in the sky, Polaris is in the same location every night from dusk till dawn, neither
rising nor setting. Its presence leads some people to think of it mistakenly as the brightest star in the sky. It's actually the brightest even so. It's about two thousand, five hundred times as luminous as our sun because it's a massive super giant with a diameter nearly forty times larger than the Sun and five times the mass. But Polaris also happens to be far away for a star that's visible with the naked eye, which reduces its brightness in our night sky. So who first noticed the north Star?
That's a complicated question. Ancient Egyptian astronomers in the Old Kingdom between forty one and forty seven hundred years ago had a north star, which they symbolically represented with a femalehipopotamus, according to Julia Magli's book Architecture, Astronomy and Sacred Landscape in Ancient Egypt. But this star was not Polarists. That's because what humans perceive as the North Star has changed
over time. We also spoke via email with Christopher Palma, a former teaching professor in astronomy who is currently Associate Dean of the Eberley College of Science at Penn State University. He said, if you picture a line connecting Earth's north and south poles as the axis around which Earth rotates, that axis is slowly moving in its own circle. Often this is compared to what happens when a top or a spinning coin starts to wobble before falling over on
their side. He explained. Because of this wobble, the imaginary line that goes from the north pole to the South pole traces out a circle once every twenty six thousand years, so Palma continued over very long time periods more than a few thousand years. The north pole moves with respect to the stars, so thousands of years ago people on Earth saw the star Thuban in the constellation Draco appear
due north instead of Polaris. Polaris seems to have been first charted by the astronomer Claudius Ptolemy, who lived from about a hundred and sixty five to eighty five b C. The star's location close to the celestial north pole eventually became useful to navigators Feinberg said, at night in the northern hemisphere, if you can see Polaris, you can always tell which way is north, and by extension, which ways
are southeast and west. It's true now, It's been true for hundreds of years, including during the age of exploration in the fifteenth through the seventeen centuries, and it will be true for hundreds more years. You can also tell your latitude, since the angle from the horizon to Polaris is the same as your latitude to within a degree anyway. Once you travel south of the equator, though, Polaris drops below the horizon, so it's no longer useful as a
navigation aid. Additionally, a navigator using Polarist has to take into account that the star isn't precisely over the north pole, but instead has an offset of thirty nine arc minutes that corresponds to an error of about forty five miles or seventy two kilometers. One of the other things that's intriguing about polarists is that it pulsates. Palma explained, this
star pulsates because it's in a state that's unstable. It will swell up, and when it does, an outer layer of the star becomes transparent, which then makes the star cool off. As a result of it cooling off, it will shrink until it becomes opaque again, which causes it to heat up and swell again. It will do this over and over, pulsating in and out, which causes its brightness to fluctuate. But Polaris won't be the north star forever.
Feinberg said, if you look at the fourteen thousand CE point, you'll see a star that's much much brighter than Polarists, but farther from the circle that's Vega, which are descend in some twelve thousand years from now, if humans are still around, will consider their north star. And as Fineberg explains, quote, it's just a coincidence that at this point in Earth's history, the north facing end of the axis happens to point
almost directly at a bright, naked eye star. The same is not currently true for the south facing end of the axis. In other words, there is no south star. Today's episode was written by Patrick J. Kaiger and produced by Tyler Clang. Brain Stuff is production of I Heart Radio's How Stuff Works. For more in this months of other topics to help navigate the world around you, visit
our home planet, how stuff Works dot com. And for more podcasts from my heart Radio, visit the I heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.