WEBVTT - Will There Always Be a North Star? 0:00:01.920 --> 0:00:06.520 Welcome to brain Stuff production of I Heart Radio. Hey, 0:00:06.559 --> 0:00:10.160 brain Stuff, Lauren bog Obam here. If you ever looked 0:00:10.200 --> 0:00:13.080 at the night sky in the Northern Hemisphere, you've probably 0:00:13.119 --> 0:00:15.640 noticed a bright star that the rest of the heavens 0:00:15.640 --> 0:00:20.080 appears to move around. What you're seeing is Polaris, also 0:00:20.120 --> 0:00:22.919 known as the North Star, which is approximately four and 0:00:22.960 --> 0:00:25.200 thirty light years away from Earth and is part of 0:00:25.239 --> 0:00:28.880 the constellation Ursa minor. The North Star is thus named 0:00:28.920 --> 0:00:31.880 because its location in the night sky is almost directly 0:00:31.960 --> 0:00:36.440 over the North Pole. We spoke via email with Rick Feinberg, 0:00:36.640 --> 0:00:39.519 a Harvard trained astronomer who is now Press Officer of 0:00:39.520 --> 0:00:43.760 the American Astronomical Society. He said, so, if you were 0:00:43.800 --> 0:00:46.680 to stand at the North Pole latitude ninety degrees north 0:00:46.720 --> 0:00:50.360 at night and look straight up, you'd see Polaris directly overhead. 0:00:51.000 --> 0:00:53.760 From other latitudes in the Northern Hemisphere, if you face 0:00:53.880 --> 0:00:55.960 due north at night and look at the same angle 0:00:56.000 --> 0:00:59.760 above the horizon as your latitude, for example, look about 0:00:59.760 --> 0:01:02.040 half way up. That's forty five degrees. If you live 0:01:02.080 --> 0:01:05.400 in Portland, Oregon, at latitude forty five degrees north, you'll 0:01:05.400 --> 0:01:10.959 see Polaris shining there. Polaris is attention getting because unlike 0:01:11.040 --> 0:01:13.680 all the other stars in the sky, Polaris is in 0:01:13.720 --> 0:01:17.040 the same location every night from dusk till dawn, neither 0:01:17.160 --> 0:01:20.720 rising nor setting. Its presence leads some people to think 0:01:20.760 --> 0:01:23.119 of it mistakenly as the brightest star in the sky. 0:01:23.440 --> 0:01:27.759 It's actually the brightest even so. It's about two thousand, 0:01:27.880 --> 0:01:30.840 five hundred times as luminous as our sun because it's 0:01:30.840 --> 0:01:33.839 a massive super giant with a diameter nearly forty times 0:01:33.920 --> 0:01:37.160 larger than the Sun and five times the mass. But 0:01:37.240 --> 0:01:40.200 Polaris also happens to be far away for a star 0:01:40.280 --> 0:01:43.160 that's visible with the naked eye, which reduces its brightness 0:01:43.160 --> 0:01:47.920 in our night sky. So who first noticed the north Star? 0:01:48.680 --> 0:01:52.480 That's a complicated question. Ancient Egyptian astronomers in the Old 0:01:52.560 --> 0:01:55.920 Kingdom between forty one and forty seven hundred years ago 0:01:56.320 --> 0:02:00.600 had a north star, which they symbolically represented with a femalehipopotamus, 0:02:00.720 --> 0:02:05.400 according to Julia Magli's book Architecture, Astronomy and Sacred Landscape 0:02:05.440 --> 0:02:10.239 in Ancient Egypt. But this star was not Polarists. That's 0:02:10.280 --> 0:02:12.960 because what humans perceive as the North Star has changed 0:02:13.000 --> 0:02:17.680 over time. We also spoke via email with Christopher Palma, 0:02:17.800 --> 0:02:20.880 a former teaching professor in astronomy who is currently Associate 0:02:20.919 --> 0:02:24.000 Dean of the Eberley College of Science at Penn State University. 0:02:24.800 --> 0:02:28.080 He said, if you picture a line connecting Earth's north 0:02:28.120 --> 0:02:31.079 and south poles as the axis around which Earth rotates, 0:02:31.639 --> 0:02:35.640 that axis is slowly moving in its own circle. Often 0:02:35.680 --> 0:02:37.880 this is compared to what happens when a top or 0:02:37.880 --> 0:02:41.160 a spinning coin starts to wobble before falling over on 0:02:41.200 --> 0:02:45.600 their side. He explained. Because of this wobble, the imaginary 0:02:45.639 --> 0:02:47.520 line that goes from the north pole to the South 0:02:47.560 --> 0:02:51.720 pole traces out a circle once every twenty six thousand years, 0:02:53.000 --> 0:02:56.560 so Palma continued over very long time periods more than 0:02:56.600 --> 0:02:59.919 a few thousand years. The north pole moves with respect 0:03:00.040 --> 0:03:03.280 to the stars, so thousands of years ago people on 0:03:03.360 --> 0:03:06.840 Earth saw the star Thuban in the constellation Draco appear 0:03:07.000 --> 0:03:12.000 due north instead of Polaris. Polaris seems to have been 0:03:12.040 --> 0:03:15.480 first charted by the astronomer Claudius Ptolemy, who lived from 0:03:15.480 --> 0:03:18.040 about a hundred and sixty five to eighty five b C. 0:03:19.520 --> 0:03:22.920 The star's location close to the celestial north pole eventually 0:03:22.960 --> 0:03:27.040 became useful to navigators Feinberg said, at night in the 0:03:27.080 --> 0:03:29.880 northern hemisphere, if you can see Polaris, you can always 0:03:29.880 --> 0:03:32.640 tell which way is north, and by extension, which ways 0:03:32.680 --> 0:03:36.240 are southeast and west. It's true now, It's been true 0:03:36.240 --> 0:03:39.200 for hundreds of years, including during the age of exploration 0:03:39.280 --> 0:03:41.920 in the fifteenth through the seventeen centuries, and it will 0:03:41.960 --> 0:03:45.000 be true for hundreds more years. You can also tell 0:03:45.040 --> 0:03:48.320 your latitude, since the angle from the horizon to Polaris 0:03:48.400 --> 0:03:51.240 is the same as your latitude to within a degree anyway. 0:03:51.640 --> 0:03:54.600 Once you travel south of the equator, though, Polaris drops 0:03:54.640 --> 0:03:56.920 below the horizon, so it's no longer useful as a 0:03:57.000 --> 0:04:01.800 navigation aid. Additionally, a navigator using Polarist has to take 0:04:01.840 --> 0:04:05.120 into account that the star isn't precisely over the north pole, 0:04:05.400 --> 0:04:08.440 but instead has an offset of thirty nine arc minutes 0:04:09.080 --> 0:04:11.880 that corresponds to an error of about forty five miles 0:04:11.960 --> 0:04:16.240 or seventy two kilometers. One of the other things that's 0:04:16.279 --> 0:04:20.920 intriguing about polarists is that it pulsates. Palma explained, this 0:04:20.960 --> 0:04:24.280 star pulsates because it's in a state that's unstable. It 0:04:24.320 --> 0:04:26.839 will swell up, and when it does, an outer layer 0:04:26.839 --> 0:04:29.279 of the star becomes transparent, which then makes the star 0:04:29.360 --> 0:04:32.280 cool off. As a result of it cooling off, it 0:04:32.279 --> 0:04:35.080 will shrink until it becomes opaque again, which causes it 0:04:35.120 --> 0:04:37.480 to heat up and swell again. It will do this 0:04:37.640 --> 0:04:40.680 over and over, pulsating in and out, which causes its 0:04:40.720 --> 0:04:45.920 brightness to fluctuate. But Polaris won't be the north star forever. 0:04:46.600 --> 0:04:50.159 Feinberg said, if you look at the fourteen thousand CE point, 0:04:50.640 --> 0:04:53.440 you'll see a star that's much much brighter than Polarists, 0:04:53.440 --> 0:04:56.919 but farther from the circle that's Vega, which are descend 0:04:56.920 --> 0:04:59.200 in some twelve thousand years from now, if humans are 0:04:59.200 --> 0:05:05.200 still around, will consider their north star. And as Fineberg explains, quote, 0:05:05.600 --> 0:05:08.560 it's just a coincidence that at this point in Earth's history, 0:05:08.839 --> 0:05:11.480 the north facing end of the axis happens to point 0:05:11.600 --> 0:05:15.360 almost directly at a bright, naked eye star. The same 0:05:15.480 --> 0:05:17.720 is not currently true for the south facing end of 0:05:17.760 --> 0:05:20.640 the axis. In other words, there is no south star. 0:05:25.960 --> 0:05:28.440 Today's episode was written by Patrick J. Kaiger and produced 0:05:28.440 --> 0:05:30.960 by Tyler Clang. Brain Stuff is production of I Heart 0:05:31.040 --> 0:05:33.280 Radio's How Stuff Works. For more in this months of 0:05:33.279 --> 0:05:35.599 other topics to help navigate the world around you, visit 0:05:35.600 --> 0:05:38.240 our home planet, how stuff Works dot com. And for 0:05:38.279 --> 0:05:40.360 more podcasts from my heart Radio, visit the I heart 0:05:40.400 --> 0:05:43.000 Radio app, Apple Podcasts, or wherever you listen to your 0:05:43.040 --> 0:05:43.719 favorite shows.