1 00:00:00,120 --> 00:00:05,080 Speaker 1: This Day in History Class is a production of iHeartRadio. 2 00:00:05,840 --> 00:00:09,559 Speaker 1: Hello and welcome to This Day in History Class, a 3 00:00:09,600 --> 00:00:12,800 Speaker 1: show that proves there's more than one way to make history. 4 00:00:15,280 --> 00:00:18,440 Speaker 1: I'm Gay Bluesier and in this episode we're looking at 5 00:00:18,440 --> 00:00:22,200 Speaker 1: an impressive achievement in early math and science. The first 6 00:00:22,320 --> 00:00:32,839 Speaker 1: credible attempt to measure the distance around our planet the 7 00:00:32,960 --> 00:00:38,559 Speaker 1: day was June nineteenth, two forty BC. Ancient Greek scholar 8 00:00:38,720 --> 00:00:43,880 Speaker 1: Eratosthenes estimated the circumference of the Earth. More than two 9 00:00:43,920 --> 00:00:47,640 Speaker 1: thousand years later, we now use man made satellites to 10 00:00:47,760 --> 00:00:51,680 Speaker 1: map and measure the Earth with pinpoint accuracy, but in 11 00:00:51,720 --> 00:00:56,040 Speaker 1: ancient Egypt, a curious polymath attempted the same feat using 12 00:00:56,080 --> 00:00:58,880 Speaker 1: nothing but a few measurements and a well placed stick 13 00:00:59,480 --> 00:01:02,680 Speaker 1: an Amazingly, the figure he came up with was only 14 00:01:02,760 --> 00:01:07,720 Speaker 1: off by less than fifty miles. Aretosthenes was born in 15 00:01:07,760 --> 00:01:11,400 Speaker 1: the Greek colony of Cyreni in modern day Libya in 16 00:01:11,520 --> 00:01:15,560 Speaker 1: around two seventy six BC. In his youth, he was 17 00:01:15,600 --> 00:01:18,920 Speaker 1: sent to Athens to study at the prestigious Plato's Academy. 18 00:01:19,560 --> 00:01:21,760 Speaker 1: At the time, the school adhered to the system of 19 00:01:21,840 --> 00:01:27,320 Speaker 1: academic skepticism, which encouraged students to question and test accepted 20 00:01:27,400 --> 00:01:30,520 Speaker 1: knowledge about the world, rather than just believing what others 21 00:01:30,560 --> 00:01:35,000 Speaker 1: claimed at face value. This hands on approach to learning 22 00:01:35,200 --> 00:01:39,680 Speaker 1: can be seen in Aritosthenes' later work, including his calculations 23 00:01:39,720 --> 00:01:45,000 Speaker 1: regarding the Earth's circumference. Some time later, Aritosthenes was called 24 00:01:45,040 --> 00:01:49,160 Speaker 1: to Egypt by Pharaoh Ptolemy the third Urugiites and appointed 25 00:01:49,280 --> 00:01:53,120 Speaker 1: as the head curator of the renowned Library of Alexandria. 26 00:01:53,880 --> 00:01:56,560 Speaker 1: He spent the rest of his life there expanding and 27 00:01:56,640 --> 00:02:00,680 Speaker 1: improving the library's vast collection, but he also found time 28 00:02:00,760 --> 00:02:04,080 Speaker 1: to continue his own studies, which covered a wide range 29 00:02:04,080 --> 00:02:09,640 Speaker 1: of disciplines. Unlike many other great scholars of antiquity, Aritosthenes 30 00:02:09,760 --> 00:02:14,000 Speaker 1: didn't specialize in a particular field. Instead, he followed the 31 00:02:14,040 --> 00:02:18,400 Speaker 1: whims of his own curiosity, engaging with everything from philosophy, 32 00:02:18,600 --> 00:02:23,960 Speaker 1: music and poetry, the geography, math, and astronomy. This led 33 00:02:24,040 --> 00:02:27,120 Speaker 1: some scholars to liken him to an athlete competing in 34 00:02:27,160 --> 00:02:31,359 Speaker 1: the pentathlon, an Olympic sport consisting of five different events, 35 00:02:32,160 --> 00:02:36,960 Speaker 1: but others were less complimentary. They thought Eritosthenes would be 36 00:02:36,960 --> 00:02:40,280 Speaker 1: better off choosing a single field to focus on. A 37 00:02:40,400 --> 00:02:44,920 Speaker 1: sentiment they mockingly expressed by nicknaming him Beta, after the 38 00:02:45,040 --> 00:02:48,360 Speaker 1: second letter of the Greek alphabet, the idea being that 39 00:02:48,440 --> 00:02:52,600 Speaker 1: he was second best at everything he did. You still 40 00:02:52,639 --> 00:02:55,880 Speaker 1: hear that kind of criticism today, with the phrase jack 41 00:02:55,919 --> 00:02:59,760 Speaker 1: of all trades, master of none. But there are benefits 42 00:02:59,760 --> 00:03:03,000 Speaker 1: to day having a more well rounded education. It can 43 00:03:03,040 --> 00:03:06,800 Speaker 1: help you recognize connections that students of a singular discipline 44 00:03:06,919 --> 00:03:11,480 Speaker 1: might overlook, and sometimes, as in Aritosthenes case, it can 45 00:03:11,560 --> 00:03:16,040 Speaker 1: lead to world changing discoveries. One day, while working in 46 00:03:16,080 --> 00:03:20,160 Speaker 1: the library, Aritosthenes learned of a curious phenomenon in the 47 00:03:20,160 --> 00:03:25,120 Speaker 1: city of Syene, just south of Alexandria. Apparently on a 48 00:03:25,160 --> 00:03:28,280 Speaker 1: particular day of the year, right at noon, the sun's 49 00:03:28,320 --> 00:03:31,400 Speaker 1: reflection was fully visible in the water at the bottom 50 00:03:31,400 --> 00:03:35,600 Speaker 1: of the town well, and the nearby sundial didn't cast 51 00:03:35,600 --> 00:03:40,080 Speaker 1: a shadow. This suggested that the sun was directly above 52 00:03:40,120 --> 00:03:45,440 Speaker 1: the city, as perfectly vertical objects don't cast shadows. The 53 00:03:45,520 --> 00:03:48,720 Speaker 1: story made Aritosthenes wonder if the same would also be 54 00:03:48,760 --> 00:03:52,160 Speaker 1: true in Alexandria, so he waited for the same day, 55 00:03:52,400 --> 00:03:56,040 Speaker 1: the summer solstice, which usually falls on June twentieth or 56 00:03:56,080 --> 00:04:00,560 Speaker 1: twenty first, and he observed that at midday the city's 57 00:04:00,600 --> 00:04:06,720 Speaker 1: obelisks and other structures did indeed cast long shadows. Aritosthenes 58 00:04:06,880 --> 00:04:10,560 Speaker 1: correctly reasoned that the difference was due to the city's location. 59 00:04:11,400 --> 00:04:15,520 Speaker 1: Alexandria was farther north than Cyine, so there the sun 60 00:04:15,720 --> 00:04:20,039 Speaker 1: wasn't exactly overhead at noon on the solstice. With that 61 00:04:20,160 --> 00:04:23,960 Speaker 1: in mind, he wisely deduced that by calculating the distance 62 00:04:24,040 --> 00:04:26,800 Speaker 1: between the two cities and the angle of the sun 63 00:04:26,920 --> 00:04:29,920 Speaker 1: at that time of year, he could determine the approximate 64 00:04:30,000 --> 00:04:35,520 Speaker 1: circumference of the entire Earth, and so in two forty BC, 65 00:04:36,080 --> 00:04:41,039 Speaker 1: Aretosthenes began gathering the necessary data. First, he hired a 66 00:04:41,080 --> 00:04:44,479 Speaker 1: man to walk from Alexandria to Syene to measure the 67 00:04:44,520 --> 00:04:48,599 Speaker 1: distance between them. The unit of measurement they used was 68 00:04:48,680 --> 00:04:52,320 Speaker 1: known as a state or stadium, and although we don't 69 00:04:52,360 --> 00:04:55,480 Speaker 1: know its exact length, historians think it was equal to 70 00:04:55,520 --> 00:04:59,039 Speaker 1: about one hundred and twenty five paces, or a little 71 00:04:59,120 --> 00:05:03,400 Speaker 1: less than a tenth of a mile. Aritosthenes is believed 72 00:05:03,440 --> 00:05:06,400 Speaker 1: to have rounded up the actual distance to an even 73 00:05:06,600 --> 00:05:10,880 Speaker 1: five thousand stadia, the equivalent of roughly five hundred miles 74 00:05:11,040 --> 00:05:16,280 Speaker 1: or eight hundred kilometers. Then, on June nineteenth, near the solstice, 75 00:05:16,560 --> 00:05:19,560 Speaker 1: he erected a pole at Alexandria and used it to 76 00:05:19,600 --> 00:05:22,920 Speaker 1: measure the angle of the Sun's rays. He did this 77 00:05:23,080 --> 00:05:25,520 Speaker 1: by dividing the length of the shadow by the height 78 00:05:25,560 --> 00:05:28,080 Speaker 1: of the pole, which gave him an angle of seven 79 00:05:28,160 --> 00:05:32,040 Speaker 1: point one to two degrees. By that point, the Greeks 80 00:05:32,080 --> 00:05:34,880 Speaker 1: had already figured out that the planet Earth was round, 81 00:05:35,160 --> 00:05:37,560 Speaker 1: and they conceived of it as a perfect circle of 82 00:05:37,640 --> 00:05:42,800 Speaker 1: three hundred and sixty degrees Aritosthenes knew that at that moment, 83 00:05:43,120 --> 00:05:46,240 Speaker 1: the angle of the Sun's rays in Syene was zero, 84 00:05:46,600 --> 00:05:50,560 Speaker 1: as the Sun was directly overhead, while in Alexandria the 85 00:05:50,600 --> 00:05:54,760 Speaker 1: angle was just over seven degrees, And since seven degrees 86 00:05:54,839 --> 00:05:58,160 Speaker 1: is about one fiftieth of three hundred and sixty degrees, 87 00:05:58,520 --> 00:06:01,479 Speaker 1: that meant the distance between the two cities had to 88 00:06:01,520 --> 00:06:06,080 Speaker 1: be one fiftieth of the distance around the Earth. From there, 89 00:06:06,200 --> 00:06:10,720 Speaker 1: it was a simple calculation. By multiplying five thousand stadia 90 00:06:10,720 --> 00:06:15,760 Speaker 1: by fifty Eritosthenes estimated Earth's circumference to be two hundred 91 00:06:15,839 --> 00:06:20,040 Speaker 1: and fifty thousand stadia, the equivalent of twenty four thousand, 92 00:06:20,120 --> 00:06:25,560 Speaker 1: eight hundred and fifty four miles or forty thousand kilometers. Now, 93 00:06:25,720 --> 00:06:30,680 Speaker 1: to be fair, those measurements weren't entirely accurate. The distance 94 00:06:30,720 --> 00:06:33,720 Speaker 1: between the two cities had been a rough estimate, and 95 00:06:33,800 --> 00:06:37,279 Speaker 1: we now know that Earth isn't perfectly spherical because it's 96 00:06:37,320 --> 00:06:40,839 Speaker 1: flattened at the poles. But we also know from the 97 00:06:40,839 --> 00:06:44,039 Speaker 1: way that Eritosthenes rounded up the numbers to make the 98 00:06:44,080 --> 00:06:47,919 Speaker 1: math easier, that he wasn't striving for perfection. He just 99 00:06:48,040 --> 00:06:51,400 Speaker 1: wanted a close estimate, and by that measure he did 100 00:06:51,440 --> 00:06:55,520 Speaker 1: remarkably well, especially given the rudimentary tools he had to 101 00:06:55,520 --> 00:06:59,279 Speaker 1: work with. We now know that the true circumference of 102 00:06:59,279 --> 00:07:02,880 Speaker 1: the Earth is twenty four nine hundred and one miles 103 00:07:03,200 --> 00:07:08,560 Speaker 1: or forty thousand, seventy five kilometers. That's pretty darn close 104 00:07:08,680 --> 00:07:11,600 Speaker 1: for a guy whose data was based on footsteps and 105 00:07:11,720 --> 00:07:16,240 Speaker 1: shadow length. In fact, his estimate was far more precise 106 00:07:16,360 --> 00:07:20,360 Speaker 1: than the ones popularized by later astronomers, including the one 107 00:07:20,440 --> 00:07:23,960 Speaker 1: used by Christopher Columbus that caused him to mistake America 108 00:07:24,240 --> 00:07:29,160 Speaker 1: for India. Aritosthenes may have been labeled beta by his peers, 109 00:07:29,360 --> 00:07:31,560 Speaker 1: but when it came to measuring the true size of 110 00:07:31,600 --> 00:07:37,880 Speaker 1: the Earth. His work was second only to a satellite. 111 00:07:39,040 --> 00:07:42,720 Speaker 1: I'm Gabelusia and hopefully you now know a little more 112 00:07:42,760 --> 00:07:46,760 Speaker 1: about history today than you did yesterday. If you'd like 113 00:07:46,800 --> 00:07:48,800 Speaker 1: to keep up with the show, you can follow us 114 00:07:48,840 --> 00:07:53,920 Speaker 1: on Twitter, Facebook, and Instagram at TDI HC Show, and 115 00:07:53,960 --> 00:07:56,680 Speaker 1: if you have any comments or suggestions, feel free to 116 00:07:56,760 --> 00:07:59,560 Speaker 1: send him my way by writing to this day at 117 00:07:59,560 --> 00:08:04,120 Speaker 1: iHeart media dot com. Thanks to Casby Bias for producing 118 00:08:04,160 --> 00:08:06,800 Speaker 1: the show, and thanks to you for listening. I'll see 119 00:08:06,840 --> 00:08:10,720 Speaker 1: you back here again tomorrow for another day in history class.