1 00:00:00,040 --> 00:00:02,600 Speaker 1: Hey, y'all. Eaves here were doubling up today with two 2 00:00:02,640 --> 00:00:07,560 Speaker 1: events in history on with the show. Hi, I'm Eves 3 00:00:07,920 --> 00:00:11,200 Speaker 1: and Welcome to This Day in History Class, a show 4 00:00:11,360 --> 00:00:14,680 Speaker 1: that uncovers a little bit more about history every day. 5 00:00:22,760 --> 00:00:28,800 Speaker 1: The day was June night, around seven fourteen in the morning, 6 00:00:29,200 --> 00:00:33,680 Speaker 1: in the atmosphere above Siberia's Potka Manya Tunguska River, and 7 00:00:33,840 --> 00:00:39,680 Speaker 1: explosion occurred. The ground shook, millions of trees were flattened, 8 00:00:40,360 --> 00:00:45,600 Speaker 1: reindeer were killed, windows shattered. Villagers in the area said 9 00:00:45,640 --> 00:00:49,720 Speaker 1: they saw smoke and flashes of light. There are no 10 00:00:49,840 --> 00:00:52,800 Speaker 1: pictures of the explosion, which came to be known as 11 00:00:52,800 --> 00:00:57,480 Speaker 1: the Tunguska event, but scientists have theorized about what caused 12 00:00:57,520 --> 00:01:01,520 Speaker 1: the blast. The Tunguska region is a remote area of 13 00:01:01,520 --> 00:01:04,679 Speaker 1: the Russian Tiger, so there were no official reports of 14 00:01:04,720 --> 00:01:08,559 Speaker 1: people dying from the explosion, though one hunter reportedly died 15 00:01:08,600 --> 00:01:12,760 Speaker 1: after he was flung against a tree. The explosion happened 16 00:01:12,800 --> 00:01:16,039 Speaker 1: at an altitude of about three to six miles or 17 00:01:16,080 --> 00:01:20,120 Speaker 1: five to ten kilometers. It's estimated to have exploded with 18 00:01:20,200 --> 00:01:23,319 Speaker 1: hundreds of times the force of the atomic bombs dropped 19 00:01:23,319 --> 00:01:27,160 Speaker 1: on Hiroshima and Nagasaki, though some estimates are way higher 20 00:01:27,200 --> 00:01:31,080 Speaker 1: and some are lower. Such estimates are hard to get 21 00:01:31,160 --> 00:01:35,160 Speaker 1: right since there was no actual impact crater. The blast 22 00:01:35,240 --> 00:01:38,880 Speaker 1: killed hundreds of reindeer, knocked down about eighty million trees 23 00:01:38,959 --> 00:01:42,520 Speaker 1: over about eight hundred square miles, and affected towns more 24 00:01:42,520 --> 00:01:46,040 Speaker 1: than thirty five miles from the event site. It was 25 00:01:46,200 --> 00:01:49,880 Speaker 1: visible from hundreds of miles away, and places in Siberia 26 00:01:49,960 --> 00:01:53,280 Speaker 1: and Europe had bright nighttime skies for a while after 27 00:01:53,320 --> 00:01:58,880 Speaker 1: the explosion. Meteorological stations in Europe even recorded seismic and 28 00:01:58,920 --> 00:02:03,800 Speaker 1: atmospheric way, but authorities did not immediately go to the 29 00:02:03,840 --> 00:02:06,400 Speaker 1: site of the event to figure out what happened. The 30 00:02:06,560 --> 00:02:10,800 Speaker 1: newspapers reported a potential impact or explosion. Tunguska was not 31 00:02:10,919 --> 00:02:14,960 Speaker 1: easily accessible and the political climate of Russia was unstable. 32 00:02:16,480 --> 00:02:21,639 Speaker 1: Russian mineralogist Leonid Kulik interviewed local eyewitnesses in nineteen one. 33 00:02:22,760 --> 00:02:26,160 Speaker 1: People who witnessed the event said they saw a fireball 34 00:02:26,480 --> 00:02:29,360 Speaker 1: that caused the ground to tremble, hot winds to blow 35 00:02:29,400 --> 00:02:33,280 Speaker 1: people over, and loud noises that sound like guns firing. 36 00:02:34,560 --> 00:02:38,440 Speaker 1: It wasn't until nineteen when a team led by Leonid 37 00:02:38,480 --> 00:02:42,160 Speaker 1: Kulik traveled to the site to investigate. They found a 38 00:02:42,240 --> 00:02:46,040 Speaker 1: large area of flattened trees, with some bear charred trees 39 00:02:46,200 --> 00:02:50,160 Speaker 1: still standing at the epicenter of the explosion. They did 40 00:02:50,160 --> 00:02:53,000 Speaker 1: not find a large crater or remnants of a meteor, 41 00:02:53,360 --> 00:02:56,000 Speaker 1: but they suggested that a meteor had exploded in the 42 00:02:56,000 --> 00:02:59,920 Speaker 1: atmosphere anyway. They explained the lack of a crater by 43 00:03:00,040 --> 00:03:03,120 Speaker 1: saying that the ground was too soft and swampy to 44 00:03:03,200 --> 00:03:06,720 Speaker 1: preserve an impact crater, and that any debris was buried. 45 00:03:07,840 --> 00:03:12,000 Speaker 1: In nineteen thirty four, Soviet scientists proposed that the extraterrestrial 46 00:03:12,040 --> 00:03:15,480 Speaker 1: body that blew up in the atmosphere was instead a comment. 47 00:03:16,240 --> 00:03:18,519 Speaker 1: Since comments are made up of ice rather than rock, 48 00:03:18,840 --> 00:03:22,280 Speaker 1: it would have vaporized when it hit the Earth. Later, 49 00:03:22,480 --> 00:03:25,800 Speaker 1: more theories cropped up. An engineer and writer said it 50 00:03:25,800 --> 00:03:29,240 Speaker 1: could have been the result of an extraterrestrial nuclear explosion. 51 00:03:30,320 --> 00:03:34,160 Speaker 1: In nineteen seventy three, physicists suggested that a black hole 52 00:03:34,280 --> 00:03:39,200 Speaker 1: had collided with Earth. Others suggested nearby Lake checa formed 53 00:03:39,240 --> 00:03:43,960 Speaker 1: after the impact, though this idea was mostly rejected and 54 00:03:44,080 --> 00:03:47,680 Speaker 1: yes some have proposed that aliens caused the explosion when 55 00:03:47,680 --> 00:03:50,640 Speaker 1: a spaceship exploded in the air, while heading to lake 56 00:03:50,680 --> 00:03:55,080 Speaker 1: by call for its fresh water. But in a team 57 00:03:55,160 --> 00:03:59,800 Speaker 1: of Ukrainian, German, and American scientists analyzed rocks collected from 58 00:03:59,800 --> 00:04:03,480 Speaker 1: this ight earlier and found that they were of meteoric origin, 59 00:04:04,640 --> 00:04:07,280 Speaker 1: but that still was not a definitive answer to the 60 00:04:07,320 --> 00:04:12,600 Speaker 1: mystery because meteor showers are not uncommon. Though debate over 61 00:04:12,640 --> 00:04:15,880 Speaker 1: the cause of the explosion continues, the consensus is that 62 00:04:16,000 --> 00:04:20,040 Speaker 1: a meteor or comment collided with substances and Earth's atmosphere 63 00:04:20,440 --> 00:04:24,480 Speaker 1: and exploded. It's thought that the cosmic body was broken 64 00:04:24,520 --> 00:04:27,880 Speaker 1: into smaller pieces as it approached the Earth's surface, and 65 00:04:28,040 --> 00:04:31,560 Speaker 1: any remnants that entered Earth's atmosphere may have been turned 66 00:04:31,560 --> 00:04:35,479 Speaker 1: into dust. The explosion is considered the largest impact of 67 00:04:35,520 --> 00:04:38,679 Speaker 1: it to happen over land in the recorded history of Earth, 68 00:04:39,240 --> 00:04:43,400 Speaker 1: even though there was no actual impact. I'm each Jeffcode 69 00:04:43,480 --> 00:04:45,960 Speaker 1: and hopefully you know a little more about history today 70 00:04:46,200 --> 00:04:50,400 Speaker 1: than you did yesterday. You can learn more about history 71 00:04:50,480 --> 00:04:55,160 Speaker 1: by following us on Twitter, Facebook, and Instagram at T 72 00:04:55,680 --> 00:05:00,280 Speaker 1: D I h C podcast. If you have a yet, 73 00:05:00,400 --> 00:05:02,400 Speaker 1: listen to a new show that I host called it 74 00:05:02,400 --> 00:05:04,920 Speaker 1: in a popular You can get it anywhere you get 75 00:05:04,960 --> 00:05:08,320 Speaker 1: this day in history class. Thank you again for listening, 76 00:05:08,360 --> 00:05:20,800 Speaker 1: and we will see you tomorrow. Hey, y'all, it's Eves. 77 00:05:21,000 --> 00:05:23,599 Speaker 1: Welcome to This Day in History Class, a podcast for 78 00:05:23,640 --> 00:05:27,039 Speaker 1: people who can never know enough about history. And it's 79 00:05:27,040 --> 00:05:30,040 Speaker 1: a super special episode today because it's the last new 80 00:05:30,080 --> 00:05:33,200 Speaker 1: episode that I'll be hosting. We will still continue to 81 00:05:33,279 --> 00:05:35,520 Speaker 1: run episodes from the vault, and you'll still hear my 82 00:05:35,680 --> 00:05:39,600 Speaker 1: voice for this reason. You'll also hear Tracy V. Wilson's voice, 83 00:05:39,640 --> 00:05:43,040 Speaker 1: who previously hosted the show, that said, it's been a 84 00:05:43,160 --> 00:05:46,159 Speaker 1: joy being immersed in so much history and getting to 85 00:05:46,200 --> 00:05:48,120 Speaker 1: share it with you, and I hope you've enjoyed it 86 00:05:48,160 --> 00:05:50,920 Speaker 1: as much as I did, and I hope that you'll 87 00:05:50,960 --> 00:05:53,920 Speaker 1: all continue to return to the show to learn about 88 00:05:53,960 --> 00:05:56,440 Speaker 1: anything you may have missed, or to give your favorite 89 00:05:56,440 --> 00:06:06,120 Speaker 1: episodes a second Listen now on with the show. The 90 00:06:06,160 --> 00:06:10,279 Speaker 1: day was June nineteen seventy two at eleven fifty nine 91 00:06:10,279 --> 00:06:13,039 Speaker 1: PM and sixty seconds. A leap second was added to 92 00:06:13,080 --> 00:06:17,480 Speaker 1: Coordinated Universal Time to synchronize clocks with earth decelerating rotation. 93 00:06:19,040 --> 00:06:22,000 Speaker 1: The second has been defined many different ways over the years. 94 00:06:22,600 --> 00:06:25,479 Speaker 1: At one point, it was defined as one eight six thousand, 95 00:06:25,480 --> 00:06:28,479 Speaker 1: four hundred of the mean solar day, but a more 96 00:06:28,480 --> 00:06:31,200 Speaker 1: precise measurement was needed because the length of a day 97 00:06:31,360 --> 00:06:36,080 Speaker 1: varies depending on many factors like seasonal and daily weather variations, 98 00:06:36,240 --> 00:06:41,080 Speaker 1: as well as oceanic and atmospheric tides. By nineteen sixty seven, 99 00:06:41,160 --> 00:06:44,360 Speaker 1: the second was defined as and I quote the duration 100 00:06:44,520 --> 00:06:48,080 Speaker 1: of nine billion, one ninety two million, six hundred and 101 00:06:48,120 --> 00:06:52,080 Speaker 1: thirty one thousand, seven hundred and seventy periods of their radiation, 102 00:06:52,320 --> 00:06:56,880 Speaker 1: corresponding to the transition between the two hyperfine levels of 103 00:06:56,920 --> 00:07:01,360 Speaker 1: the ground state of the ses M one thirty three atom. 104 00:07:01,360 --> 00:07:04,320 Speaker 1: This was the measurement that the International System of Units 105 00:07:04,440 --> 00:07:07,720 Speaker 1: or s I used. Since then, the wording of the 106 00:07:07,760 --> 00:07:12,320 Speaker 1: official definition has been updated slightly. Atomic clocks keep time 107 00:07:12,360 --> 00:07:16,480 Speaker 1: with extreme precision. On atomic clocks, a day is exactly 108 00:07:16,680 --> 00:07:21,200 Speaker 1: eighty six thousand, four hundred s I seconds. International atomic 109 00:07:21,280 --> 00:07:24,480 Speaker 1: time is a time scale that is computed by taking 110 00:07:24,480 --> 00:07:27,840 Speaker 1: the weighted average of more than four hundred atomic clocks 111 00:07:27,880 --> 00:07:32,720 Speaker 1: around the world. It's not connected to any astronomical observations. 112 00:07:33,720 --> 00:07:36,640 Speaker 1: Universal time, on the other hand, is a time standard 113 00:07:36,720 --> 00:07:41,720 Speaker 1: that is based on Earth's rotation and astronomical observations. Coordinated 114 00:07:41,800 --> 00:07:46,200 Speaker 1: universal time or UTC, is under the umbrella of universal time, 115 00:07:46,560 --> 00:07:50,080 Speaker 1: which also includes UT zero, U T one, U T 116 00:07:50,280 --> 00:07:54,000 Speaker 1: one R, and U T two. Unlike other versions of 117 00:07:54,080 --> 00:07:59,280 Speaker 1: universal time, UTC is determined by International Atomic Time. Though 118 00:07:59,320 --> 00:08:03,360 Speaker 1: the practice of UTC was already being coordinated internationally, the 119 00:08:03,440 --> 00:08:08,240 Speaker 1: International Astronomical Union didn't adopt the name coordinated Universal Time 120 00:08:08,360 --> 00:08:13,040 Speaker 1: until nineteen sixty seven. Coordinated Universal time is the primary 121 00:08:13,080 --> 00:08:17,480 Speaker 1: standard by which the world regulates time, but Earth's rotation, 122 00:08:17,640 --> 00:08:21,200 Speaker 1: as measured by UT one, is gradually slowing, so that 123 00:08:21,240 --> 00:08:24,280 Speaker 1: the length of a rotational day is about two milliseconds 124 00:08:24,360 --> 00:08:27,480 Speaker 1: longer than the eighty six thousand, four hundred seconds it 125 00:08:27,640 --> 00:08:31,320 Speaker 1: was two centuries ago. That means that there's a discrepancy 126 00:08:31,440 --> 00:08:37,200 Speaker 1: between UTC and UT one. Scientists determined that UTC would 127 00:08:37,200 --> 00:08:40,120 Speaker 1: have to be adjusted to account for the difference between 128 00:08:40,120 --> 00:08:43,800 Speaker 1: the definition of the second and Earth's rotation. This keeps 129 00:08:43,920 --> 00:08:46,640 Speaker 1: UTC in line with the apparent position of the Sun 130 00:08:46,760 --> 00:08:49,800 Speaker 1: and stars. In other words, a second would need to 131 00:08:49,800 --> 00:08:52,760 Speaker 1: be added to or removed from clocks to realign them 132 00:08:52,760 --> 00:08:58,400 Speaker 1: with Earth's rotation. Occasionally, scientists specified that UTC should not 133 00:08:58,559 --> 00:09:02,080 Speaker 1: deviate more than nine of a second from UT one, 134 00:09:02,440 --> 00:09:05,760 Speaker 1: So on June thirtieth, nineteen seventy two, the first leap 135 00:09:05,840 --> 00:09:10,240 Speaker 1: second was added to UTC. The International Earth Rotation and 136 00:09:10,320 --> 00:09:13,840 Speaker 1: Reference System Service decides when to add a leap second. 137 00:09:14,440 --> 00:09:18,440 Speaker 1: One is typically added either on June or December thirty one. 138 00:09:19,320 --> 00:09:22,600 Speaker 1: From nineteen seventy two to nineteen ninety nine, leap seconds 139 00:09:22,640 --> 00:09:24,840 Speaker 1: were added at a rate of about one per year. 140 00:09:25,480 --> 00:09:28,880 Speaker 1: After that, they've been added less frequently. There have been 141 00:09:29,000 --> 00:09:32,560 Speaker 1: twenty seven leap seconds since nineteen seventy two. The most 142 00:09:32,679 --> 00:09:37,520 Speaker 1: recent leap second was added on December thirty one. Many 143 00:09:37,559 --> 00:09:40,200 Speaker 1: people have called for the elimination of leap seconds and 144 00:09:40,280 --> 00:09:43,920 Speaker 1: the replacement of UTC with a new system. Leap seconds 145 00:09:43,920 --> 00:09:47,440 Speaker 1: have caused problems for some computer systems since they're not 146 00:09:47,520 --> 00:09:51,520 Speaker 1: that predictable and can't be anticipated far in advance, and 147 00:09:51,679 --> 00:09:54,520 Speaker 1: they'll need to be added more frequently as Earth's rotation 148 00:09:54,600 --> 00:09:58,720 Speaker 1: continues to slow down. Some people who support abolishing leap 149 00:09:58,760 --> 00:10:01,960 Speaker 1: seconds argue that it doesn't matter whether our perception of 150 00:10:02,000 --> 00:10:05,240 Speaker 1: time changes along with the rotation of Earth, since that 151 00:10:05,280 --> 00:10:10,120 Speaker 1: would happen over a long time anyway. I'm Eves Jeff Coo, 152 00:10:10,360 --> 00:10:13,080 Speaker 1: and hopefully you know a little more about history today 153 00:10:13,400 --> 00:10:16,320 Speaker 1: than you did yesterday, and if you have any commerce 154 00:10:16,360 --> 00:10:18,480 Speaker 1: oar suggestions, you can send them to us at this 155 00:10:18,600 --> 00:10:21,000 Speaker 1: day and I heart media dot com. You can also 156 00:10:21,080 --> 00:10:24,000 Speaker 1: hit us up on social media where at t D 157 00:10:24,040 --> 00:10:27,240 Speaker 1: I h C podcast. Also a shout out to the 158 00:10:27,280 --> 00:10:31,120 Speaker 1: extraordinary producers of this show, Alexis and Chandler, who y'all 159 00:10:31,120 --> 00:10:33,360 Speaker 1: never get to hear but are a huge part of 160 00:10:33,360 --> 00:10:35,320 Speaker 1: why you love the show and are still listening to it. 161 00:10:36,360 --> 00:10:38,439 Speaker 1: Thanks to Kenni for listening to the show and we'll 162 00:10:38,440 --> 00:10:53,040 Speaker 1: see you tomorrow. For more podcasts from I Heart Radio, 163 00:10:53,200 --> 00:10:55,800 Speaker 1: visit the iHeart Radio app, Apple Podcasts, or wherever you 164 00:10:55,840 --> 00:10:56,960 Speaker 1: listen to your favorite shows.