Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey,
Speaker 1: brain Stuff, Lauren bog Obam here. If you ever looked
Speaker 1: at the night sky in the Northern Hemisphere, you've probably
Speaker 1: noticed a bright star that the rest of the heavens
Speaker 1: appears to move around. What you're seeing is Polaris, also
Speaker 1: known as the North Star, which is approximately four and
Speaker 1: thirty light years away from Earth and is part of
Speaker 1: the constellation Ursa minor. The North Star is thus named
Speaker 1: because its location in the night sky is almost directly
Speaker 1: over the North Pole. We spoke via email with Rick Feinberg,
Speaker 1: a Harvard trained astronomer who is now Press Officer of
Speaker 1: the American Astronomical Society. He said, so, if you were
Speaker 1: to stand at the North Pole latitude ninety degrees north
Speaker 1: at night and look straight up, you'd see Polaris directly overhead.
Speaker 1: From other latitudes in the Northern Hemisphere, if you face
Speaker 1: due north at night and look at the same angle
Speaker 1: above the horizon as your latitude, for example, look about
Speaker 1: half way up. That's forty five degrees. If you live
Speaker 1: in Portland, Oregon, at latitude forty five degrees north, you'll
Speaker 1: see Polaris shining there. Polaris is attention getting because unlike
Speaker 1: all the other stars in the sky, Polaris is in
Speaker 1: the same location every night from dusk till dawn, neither
Speaker 1: rising nor setting. Its presence leads some people to think
Speaker 1: of it mistakenly as the brightest star in the sky.
Speaker 1: It's actually the brightest even so. It's about two thousand,
Speaker 1: five hundred times as luminous as our sun because it's
Speaker 1: a massive super giant with a diameter nearly forty times
Speaker 1: larger than the Sun and five times the mass. But
Speaker 1: Polaris also happens to be far away for a star
Speaker 1: that's visible with the naked eye, which reduces its brightness
Speaker 1: in our night sky. So who first noticed the north Star?
Speaker 1: That's a complicated question. Ancient Egyptian astronomers in the Old
Speaker 1: Kingdom between forty one and forty seven hundred years ago
Speaker 1: had a north star, which they symbolically represented with a femalehipopotamus,
Speaker 1: according to Julia Magli's book Architecture, Astronomy and Sacred Landscape
Speaker 1: in Ancient Egypt. But this star was not Polarists. That's
Speaker 1: because what humans perceive as the North Star has changed
Speaker 1: over time. We also spoke via email with Christopher Palma,
Speaker 1: a former teaching professor in astronomy who is currently Associate
Speaker 1: Dean of the Eberley College of Science at Penn State University.
Speaker 1: He said, if you picture a line connecting Earth's north
Speaker 1: and south poles as the axis around which Earth rotates,
Speaker 1: that axis is slowly moving in its own circle. Often
Speaker 1: this is compared to what happens when a top or
Speaker 1: a spinning coin starts to wobble before falling over on
Speaker 1: their side. He explained. Because of this wobble, the imaginary
Speaker 1: line that goes from the north pole to the South
Speaker 1: pole traces out a circle once every twenty six thousand years,
Speaker 1: so Palma continued over very long time periods more than
Speaker 1: a few thousand years. The north pole moves with respect
Speaker 1: to the stars, so thousands of years ago people on
Speaker 1: Earth saw the star Thuban in the constellation Draco appear
Speaker 1: due north instead of Polaris. Polaris seems to have been
Speaker 1: first charted by the astronomer Claudius Ptolemy, who lived from
Speaker 1: about a hundred and sixty five to eighty five b C.
Speaker 1: The star's location close to the celestial north pole eventually
Speaker 1: became useful to navigators Feinberg said, at night in the
Speaker 1: northern hemisphere, if you can see Polaris, you can always
Speaker 1: tell which way is north, and by extension, which ways
Speaker 1: are southeast and west. It's true now, It's been true
Speaker 1: for hundreds of years, including during the age of exploration
Speaker 1: in the fifteenth through the seventeen centuries, and it will
Speaker 1: be true for hundreds more years. You can also tell
Speaker 1: your latitude, since the angle from the horizon to Polaris
Speaker 1: is the same as your latitude to within a degree anyway.
Speaker 1: Once you travel south of the equator, though, Polaris drops
Speaker 1: below the horizon, so it's no longer useful as a
Speaker 1: navigation aid. Additionally, a navigator using Polarist has to take
Speaker 1: into account that the star isn't precisely over the north pole,
Speaker 1: but instead has an offset of thirty nine arc minutes
Speaker 1: that corresponds to an error of about forty five miles
Speaker 1: or seventy two kilometers. One of the other things that's
Speaker 1: intriguing about polarists is that it pulsates. Palma explained, this
Speaker 1: star pulsates because it's in a state that's unstable. It
Speaker 1: will swell up, and when it does, an outer layer
Speaker 1: of the star becomes transparent, which then makes the star
Speaker 1: cool off. As a result of it cooling off, it
Speaker 1: will shrink until it becomes opaque again, which causes it
Speaker 1: to heat up and swell again. It will do this
Speaker 1: over and over, pulsating in and out, which causes its
Speaker 1: brightness to fluctuate. But Polaris won't be the north star forever.
Speaker 1: Feinberg said, if you look at the fourteen thousand CE point,
Speaker 1: you'll see a star that's much much brighter than Polarists,
Speaker 1: but farther from the circle that's Vega, which are descend
Speaker 1: in some twelve thousand years from now, if humans are
Speaker 1: still around, will consider their north star. And as Fineberg explains, quote,
Speaker 1: it's just a coincidence that at this point in Earth's history,
Speaker 1: the north facing end of the axis happens to point
Speaker 1: almost directly at a bright, naked eye star. The same
Speaker 1: is not currently true for the south facing end of
Speaker 1: the axis. In other words, there is no south star.
Speaker 1: Today's episode was written by Patrick J. Kaiger and produced
Speaker 1: by Tyler Clang. Brain Stuff is production of I Heart
Speaker 1: Radio's How Stuff Works. For more in this months of
Speaker 1: other topics to help navigate the world around you, visit
Speaker 1: our home planet, how stuff Works dot com. And for
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