1 00:00:01,920 --> 00:00:06,520 Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey, 2 00:00:06,559 --> 00:00:10,160 Speaker 1: brain Stuff, Lauren bog Obam here. If you ever looked 3 00:00:10,200 --> 00:00:13,080 Speaker 1: at the night sky in the Northern Hemisphere, you've probably 4 00:00:13,119 --> 00:00:15,640 Speaker 1: noticed a bright star that the rest of the heavens 5 00:00:15,640 --> 00:00:20,080 Speaker 1: appears to move around. What you're seeing is Polaris, also 6 00:00:20,120 --> 00:00:22,919 Speaker 1: known as the North Star, which is approximately four and 7 00:00:22,960 --> 00:00:25,200 Speaker 1: thirty light years away from Earth and is part of 8 00:00:25,239 --> 00:00:28,880 Speaker 1: the constellation Ursa minor. The North Star is thus named 9 00:00:28,920 --> 00:00:31,880 Speaker 1: because its location in the night sky is almost directly 10 00:00:31,960 --> 00:00:36,440 Speaker 1: over the North Pole. We spoke via email with Rick Feinberg, 11 00:00:36,640 --> 00:00:39,519 Speaker 1: a Harvard trained astronomer who is now Press Officer of 12 00:00:39,520 --> 00:00:43,760 Speaker 1: the American Astronomical Society. He said, so, if you were 13 00:00:43,800 --> 00:00:46,680 Speaker 1: to stand at the North Pole latitude ninety degrees north 14 00:00:46,720 --> 00:00:50,360 Speaker 1: at night and look straight up, you'd see Polaris directly overhead. 15 00:00:51,000 --> 00:00:53,760 Speaker 1: From other latitudes in the Northern Hemisphere, if you face 16 00:00:53,880 --> 00:00:55,960 Speaker 1: due north at night and look at the same angle 17 00:00:56,000 --> 00:00:59,760 Speaker 1: above the horizon as your latitude, for example, look about 18 00:00:59,760 --> 00:01:02,040 Speaker 1: half way up. That's forty five degrees. If you live 19 00:01:02,080 --> 00:01:05,400 Speaker 1: in Portland, Oregon, at latitude forty five degrees north, you'll 20 00:01:05,400 --> 00:01:10,959 Speaker 1: see Polaris shining there. Polaris is attention getting because unlike 21 00:01:11,040 --> 00:01:13,680 Speaker 1: all the other stars in the sky, Polaris is in 22 00:01:13,720 --> 00:01:17,040 Speaker 1: the same location every night from dusk till dawn, neither 23 00:01:17,160 --> 00:01:20,720 Speaker 1: rising nor setting. Its presence leads some people to think 24 00:01:20,760 --> 00:01:23,119 Speaker 1: of it mistakenly as the brightest star in the sky. 25 00:01:23,440 --> 00:01:27,759 Speaker 1: It's actually the brightest even so. It's about two thousand, 26 00:01:27,880 --> 00:01:30,840 Speaker 1: five hundred times as luminous as our sun because it's 27 00:01:30,840 --> 00:01:33,839 Speaker 1: a massive super giant with a diameter nearly forty times 28 00:01:33,920 --> 00:01:37,160 Speaker 1: larger than the Sun and five times the mass. But 29 00:01:37,240 --> 00:01:40,200 Speaker 1: Polaris also happens to be far away for a star 30 00:01:40,280 --> 00:01:43,160 Speaker 1: that's visible with the naked eye, which reduces its brightness 31 00:01:43,160 --> 00:01:47,920 Speaker 1: in our night sky. So who first noticed the north Star? 32 00:01:48,680 --> 00:01:52,480 Speaker 1: That's a complicated question. Ancient Egyptian astronomers in the Old 33 00:01:52,560 --> 00:01:55,920 Speaker 1: Kingdom between forty one and forty seven hundred years ago 34 00:01:56,320 --> 00:02:00,600 Speaker 1: had a north star, which they symbolically represented with a femalehipopotamus, 35 00:02:00,720 --> 00:02:05,400 Speaker 1: according to Julia Magli's book Architecture, Astronomy and Sacred Landscape 36 00:02:05,440 --> 00:02:10,239 Speaker 1: in Ancient Egypt. But this star was not Polarists. That's 37 00:02:10,280 --> 00:02:12,960 Speaker 1: because what humans perceive as the North Star has changed 38 00:02:13,000 --> 00:02:17,680 Speaker 1: over time. We also spoke via email with Christopher Palma, 39 00:02:17,800 --> 00:02:20,880 Speaker 1: a former teaching professor in astronomy who is currently Associate 40 00:02:20,919 --> 00:02:24,000 Speaker 1: Dean of the Eberley College of Science at Penn State University. 41 00:02:24,800 --> 00:02:28,080 Speaker 1: He said, if you picture a line connecting Earth's north 42 00:02:28,120 --> 00:02:31,079 Speaker 1: and south poles as the axis around which Earth rotates, 43 00:02:31,639 --> 00:02:35,640 Speaker 1: that axis is slowly moving in its own circle. Often 44 00:02:35,680 --> 00:02:37,880 Speaker 1: this is compared to what happens when a top or 45 00:02:37,880 --> 00:02:41,160 Speaker 1: a spinning coin starts to wobble before falling over on 46 00:02:41,200 --> 00:02:45,600 Speaker 1: their side. He explained. Because of this wobble, the imaginary 47 00:02:45,639 --> 00:02:47,520 Speaker 1: line that goes from the north pole to the South 48 00:02:47,560 --> 00:02:51,720 Speaker 1: pole traces out a circle once every twenty six thousand years, 49 00:02:53,000 --> 00:02:56,560 Speaker 1: so Palma continued over very long time periods more than 50 00:02:56,600 --> 00:02:59,919 Speaker 1: a few thousand years. The north pole moves with respect 51 00:03:00,040 --> 00:03:03,280 Speaker 1: to the stars, so thousands of years ago people on 52 00:03:03,360 --> 00:03:06,840 Speaker 1: Earth saw the star Thuban in the constellation Draco appear 53 00:03:07,000 --> 00:03:12,000 Speaker 1: due north instead of Polaris. Polaris seems to have been 54 00:03:12,040 --> 00:03:15,480 Speaker 1: first charted by the astronomer Claudius Ptolemy, who lived from 55 00:03:15,480 --> 00:03:18,040 Speaker 1: about a hundred and sixty five to eighty five b C. 56 00:03:19,520 --> 00:03:22,920 Speaker 1: The star's location close to the celestial north pole eventually 57 00:03:22,960 --> 00:03:27,040 Speaker 1: became useful to navigators Feinberg said, at night in the 58 00:03:27,080 --> 00:03:29,880 Speaker 1: northern hemisphere, if you can see Polaris, you can always 59 00:03:29,880 --> 00:03:32,640 Speaker 1: tell which way is north, and by extension, which ways 60 00:03:32,680 --> 00:03:36,240 Speaker 1: are southeast and west. It's true now, It's been true 61 00:03:36,240 --> 00:03:39,200 Speaker 1: for hundreds of years, including during the age of exploration 62 00:03:39,280 --> 00:03:41,920 Speaker 1: in the fifteenth through the seventeen centuries, and it will 63 00:03:41,960 --> 00:03:45,000 Speaker 1: be true for hundreds more years. You can also tell 64 00:03:45,040 --> 00:03:48,320 Speaker 1: your latitude, since the angle from the horizon to Polaris 65 00:03:48,400 --> 00:03:51,240 Speaker 1: is the same as your latitude to within a degree anyway. 66 00:03:51,640 --> 00:03:54,600 Speaker 1: Once you travel south of the equator, though, Polaris drops 67 00:03:54,640 --> 00:03:56,920 Speaker 1: below the horizon, so it's no longer useful as a 68 00:03:57,000 --> 00:04:01,800 Speaker 1: navigation aid. Additionally, a navigator using Polarist has to take 69 00:04:01,840 --> 00:04:05,120 Speaker 1: into account that the star isn't precisely over the north pole, 70 00:04:05,400 --> 00:04:08,440 Speaker 1: but instead has an offset of thirty nine arc minutes 71 00:04:09,080 --> 00:04:11,880 Speaker 1: that corresponds to an error of about forty five miles 72 00:04:11,960 --> 00:04:16,240 Speaker 1: or seventy two kilometers. One of the other things that's 73 00:04:16,279 --> 00:04:20,920 Speaker 1: intriguing about polarists is that it pulsates. Palma explained, this 74 00:04:20,960 --> 00:04:24,280 Speaker 1: star pulsates because it's in a state that's unstable. It 75 00:04:24,320 --> 00:04:26,839 Speaker 1: will swell up, and when it does, an outer layer 76 00:04:26,839 --> 00:04:29,279 Speaker 1: of the star becomes transparent, which then makes the star 77 00:04:29,360 --> 00:04:32,280 Speaker 1: cool off. As a result of it cooling off, it 78 00:04:32,279 --> 00:04:35,080 Speaker 1: will shrink until it becomes opaque again, which causes it 79 00:04:35,120 --> 00:04:37,480 Speaker 1: to heat up and swell again. It will do this 80 00:04:37,640 --> 00:04:40,680 Speaker 1: over and over, pulsating in and out, which causes its 81 00:04:40,720 --> 00:04:45,920 Speaker 1: brightness to fluctuate. But Polaris won't be the north star forever. 82 00:04:46,600 --> 00:04:50,159 Speaker 1: Feinberg said, if you look at the fourteen thousand CE point, 83 00:04:50,640 --> 00:04:53,440 Speaker 1: you'll see a star that's much much brighter than Polarists, 84 00:04:53,440 --> 00:04:56,919 Speaker 1: but farther from the circle that's Vega, which are descend 85 00:04:56,920 --> 00:04:59,200 Speaker 1: in some twelve thousand years from now, if humans are 86 00:04:59,200 --> 00:05:05,200 Speaker 1: still around, will consider their north star. And as Fineberg explains, quote, 87 00:05:05,600 --> 00:05:08,560 Speaker 1: it's just a coincidence that at this point in Earth's history, 88 00:05:08,839 --> 00:05:11,480 Speaker 1: the north facing end of the axis happens to point 89 00:05:11,600 --> 00:05:15,360 Speaker 1: almost directly at a bright, naked eye star. The same 90 00:05:15,480 --> 00:05:17,720 Speaker 1: is not currently true for the south facing end of 91 00:05:17,760 --> 00:05:20,640 Speaker 1: the axis. In other words, there is no south star. 92 00:05:25,960 --> 00:05:28,440 Speaker 1: Today's episode was written by Patrick J. Kaiger and produced 93 00:05:28,440 --> 00:05:30,960 Speaker 1: by Tyler Clang. Brain Stuff is production of I Heart 94 00:05:31,040 --> 00:05:33,280 Speaker 1: Radio's How Stuff Works. For more in this months of 95 00:05:33,279 --> 00:05:35,599 Speaker 1: other topics to help navigate the world around you, visit 96 00:05:35,600 --> 00:05:38,240 Speaker 1: our home planet, how stuff Works dot com. And for 97 00:05:38,279 --> 00:05:40,360 Speaker 1: more podcasts from my heart Radio, visit the I heart 98 00:05:40,400 --> 00:05:43,000 Speaker 1: Radio app, Apple Podcasts, or wherever you listen to your 99 00:05:43,040 --> 00:05:43,719 Speaker 1: favorite shows.