WEBVTT - Why Does the Week Have 7 Days? 0:00:01.160 --> 0:00:04.760 Hey, welcome to Sign Stuff, a production of iHeartRadio. I'm 0:00:04.760 --> 0:00:07.800 hoorheit him and today we're asking the question why does 0:00:07.880 --> 0:00:12.200 the week have seven days? Why not six days or nine? 0:00:12.760 --> 0:00:15.240 It's part of a larger episode in which we explore 0:00:15.480 --> 0:00:18.760 the signs behind the time units we use in our 0:00:18.800 --> 0:00:22.320 everyday lives. For example, we're gonna answer the question why 0:00:22.400 --> 0:00:26.000 is a second called a second? Or is it day 0:00:26.239 --> 0:00:30.040 actually one full rotation of the Earth. As we'll learn, 0:00:30.200 --> 0:00:32.400 there are all kinds of surprises in the way we 0:00:32.479 --> 0:00:35.760 keep track of time. So set your clocks, take a 0:00:35.840 --> 0:00:39.240 minute with us, because the hour has come to answer 0:00:39.280 --> 0:00:50.880 the question why does the week have seven days? Hi? Everyone, 0:00:51.159 --> 0:00:54.160 Today we're going to explore the signs behind the time 0:00:54.280 --> 0:00:57.440 units we use in our everyday lives. We're gonna learn 0:00:57.480 --> 0:01:01.040 things like why does a minute have sixty second? Or 0:01:01.080 --> 0:01:03.080 why are there twelve months to a year? 0:01:03.760 --> 0:01:03.960 Now? 0:01:04.000 --> 0:01:06.120 As it turns out, a lot of time units we 0:01:06.240 --> 0:01:10.000 use have their origin in the movement of celestial bodies 0:01:10.040 --> 0:01:12.800 in space, which is why our guide for today is 0:01:12.800 --> 0:01:16.960 my friend, Professor Matt Siegler, a planetary scientist at the 0:01:17.080 --> 0:01:21.560 University of Hawaii. Here's what he does. Well, Thank you, 0:01:21.600 --> 0:01:22.840 doctor Siegler for joining us. 0:01:23.120 --> 0:01:25.720 Thank you for having me. My name is Matt Siegler. 0:01:25.800 --> 0:01:30.479 I'm a professor at University Hawaii and I studied planets. 0:01:30.720 --> 0:01:34.039 So I work on about ten different spacecraft missions that 0:01:34.080 --> 0:01:38.160 are going to the Moon or Mars or Jupiter's moons. 0:01:38.200 --> 0:01:40.680 So you based out of Hawaii, but you work with NASA, 0:01:40.720 --> 0:01:42.080 and yeah. 0:01:41.760 --> 0:01:44.880 So most projects are going to be through NASA projects. 0:01:45.040 --> 0:01:48.280 And then I'm working on the Canadian rover that's going 0:01:48.360 --> 0:01:50.840 to the south pole of the Moon and roughly twenty 0:01:50.880 --> 0:01:54.840 twenty seven, and occasionally I've worked with some ISSA missions. Uh. 0:01:55.040 --> 0:01:59.200 Interesting, in ISSA means what ISSA is European Space Agency. Well, 0:01:59.240 --> 0:02:01.320 the reason I thought you for this topic was that 0:02:01.480 --> 0:02:06.320 you're expert on planets, and I imagine that time is 0:02:06.440 --> 0:02:09.000 very important when you're thinking about the different planets, Like 0:02:09.040 --> 0:02:11.080 you have to think about how long the rotation of 0:02:11.120 --> 0:02:14.000 Mars takes or how long does the Moon go around 0:02:14.040 --> 0:02:15.840 the Earth to be able to talk to it right. 0:02:16.040 --> 0:02:19.280 Oh, yeah, your spacecraft might be orbiting at a certain 0:02:19.360 --> 0:02:21.920 rate around the Moon or you might be landed on 0:02:21.960 --> 0:02:23.880 the Moon or Mars, and then you need to care 0:02:23.919 --> 0:02:26.760 about what the day night cycle is. But then also 0:02:26.840 --> 0:02:29.840 you're thinking about, you know, when Will has come to 0:02:29.919 --> 0:02:32.239 view of Earth and when we'll be able to talk 0:02:32.280 --> 0:02:35.200 to it, or maybe you're waiting for a satellite that's 0:02:35.200 --> 0:02:37.480 going around Mars to come overhead that you talk to. 0:02:37.639 --> 0:02:38.000 It's. 0:02:38.240 --> 0:02:42.639 Yeah, there's a lot of complicated timekeeping, all right. 0:02:42.720 --> 0:02:45.280 So the first unit of time doctor Siegier and I 0:02:45.360 --> 0:02:48.960 talked about was the day. Most people think that a 0:02:49.080 --> 0:02:51.480 day is how much time it takes for the Earth 0:02:51.680 --> 0:02:55.239 to spin and do a full rotation, but actually that's 0:02:55.280 --> 0:03:00.920 not really true. Let's start with the day. Why did 0:03:00.960 --> 0:03:01.880 you want to start with the day? 0:03:02.040 --> 0:03:04.600 So the day is kind of an obvious place to start, 0:03:04.680 --> 0:03:07.480 because that is the most simple thing of you look 0:03:07.520 --> 0:03:09.880 at the sun and you wanted to come back to 0:03:09.960 --> 0:03:13.040 noon the next day, Right, that will happen in a 0:03:13.040 --> 0:03:16.440 certain amount of time. But early on we realized that 0:03:16.440 --> 0:03:18.560 that was actually different than if you looked at a 0:03:18.639 --> 0:03:22.160 star and wanted that star to come back overhead. Those 0:03:22.200 --> 0:03:24.360 two things were just a little bit different. 0:03:25.680 --> 0:03:28.520 Okay, so it turns out there are actually two days 0:03:28.600 --> 0:03:31.200 here on Earth. The first is the time it takes 0:03:31.240 --> 0:03:33.840 with the Earth to do a full rotation as it 0:03:33.840 --> 0:03:37.680 spends relative to stay. The rest of the universe. That's 0:03:37.720 --> 0:03:41.000 called this ideial day or the star day. And then 0:03:41.040 --> 0:03:42.920 there's a time it takes for us to see the 0:03:42.960 --> 0:03:47.400 Sun at its highest position or high noon. Those two 0:03:47.400 --> 0:03:51.800 are different because the Earth is moving around the Sun. 0:03:54.160 --> 0:03:56.920 Those are a little different. And you have to imagine 0:03:57.040 --> 0:04:00.600 how the system works. If you're spinning around on the Earth. 0:04:00.760 --> 0:04:01.200 Uh huh. 0:04:01.240 --> 0:04:04.360 If you're just the Earth spinning, it actually takes twenty 0:04:04.360 --> 0:04:07.840 three hours and fifty six minutes roughly for you to 0:04:07.880 --> 0:04:10.520 get back to the same place. The Earth spins on 0:04:10.600 --> 0:04:13.720 its axis once every twenty three hours and fifty six minutes. 0:04:13.880 --> 0:04:18.440 What yeah, what, And it's the fact that we're moving 0:04:18.640 --> 0:04:22.240 around the Sun. It takes a little bit longer each 0:04:22.360 --> 0:04:24.880 day for us to point back at the Sun again. 0:04:25.400 --> 0:04:28.920 And so here's this combination of the Earth's motion around 0:04:29.000 --> 0:04:32.080 the Sun and the spinning of the Earth that come 0:04:32.160 --> 0:04:34.479 together to give us a day which is just the 0:04:34.560 --> 0:04:36.840 solar day, which is a little bit longer than how 0:04:36.880 --> 0:04:38.120 long it takes for us to spin. 0:04:38.600 --> 0:04:40.960 What wait wait wait, wait wait wait wait, you just 0:04:41.000 --> 0:04:44.400 blew my mind and we just started this is crazy 0:04:44.680 --> 0:04:45.919 wait wait. 0:04:46.120 --> 0:04:47.920 Yeah, we really need one of your animations. 0:04:49.800 --> 0:04:54.560 This is where being a cartoonist is extra frustrating. Okay, 0:04:54.640 --> 0:04:58.320 here's what's going on to Earth actually takes twenty three 0:04:58.400 --> 0:05:02.359 hours and fifty six minutes to spin around on its axis. 0:05:02.880 --> 0:05:05.599 But because we're also going around the Sun, by the 0:05:05.640 --> 0:05:08.719 time we spin around, the Sun is now a little 0:05:08.720 --> 0:05:11.280 bit behind us, and so it takes a little bit 0:05:11.279 --> 0:05:14.799 of extra time to catch it again at high noon. 0:05:16.680 --> 0:05:19.919 And so because at the same time, we move a 0:05:19.920 --> 0:05:22.680 little way around the Sun, roughly a degree or so, 0:05:23.080 --> 0:05:25.640 it takes a little bit of extra time for us 0:05:25.680 --> 0:05:28.839 to come back and point to the Sun because we've 0:05:28.880 --> 0:05:31.840 moved a little ways around, And so that extra time 0:05:32.000 --> 0:05:34.599 is four minutes every day, no. 0:05:34.720 --> 0:05:36.680 Kidding, Wait, I guess it's sort of like the Sun 0:05:36.920 --> 0:05:40.920 moved around relative to us in the solar system. Yeah. 0:05:41.040 --> 0:05:43.080 So let's say you're jogging down the street and you 0:05:43.200 --> 0:05:45.960 see a crazy looking dog or something, and you're going 0:05:45.960 --> 0:05:48.680 to turn your head backward a little to look because 0:05:48.680 --> 0:05:52.640 you ran past. Right. Oh, you have to turn a 0:05:52.680 --> 0:05:56.240 little more than if you're just standing right next to 0:05:56.279 --> 0:05:56.760 that dog. 0:05:57.040 --> 0:05:58.680 I see, So we have to turn a little bit 0:05:58.680 --> 0:06:02.800 more to complete the noon cycle. Yeah, and it's four minutes. 0:06:02.920 --> 0:06:04.120 That seems like a lot. 0:06:04.040 --> 0:06:07.240 I know, and that's basically based on the ratio between 0:06:07.520 --> 0:06:11.000 the day and the year. But it gets even crazier. 0:06:12.040 --> 0:06:15.440 Yes, it gets crazier. Not only is a day not 0:06:15.680 --> 0:06:18.520 really a day, but it also depends on what time 0:06:18.560 --> 0:06:20.000 of the year it is. 0:06:21.760 --> 0:06:23.680 Kepler was the one that did most of the math 0:06:23.760 --> 0:06:26.960 behind it, and he figured out that the Earth's orbit 0:06:27.400 --> 0:06:30.200 is not a perfect circle. So this adds an extra 0:06:30.240 --> 0:06:33.000 complication of this. When we're going around the Sun, you 0:06:33.279 --> 0:06:36.280 go at a little bit different speeds depending on if 0:06:36.320 --> 0:06:38.200 you're at the near part of that oval or the 0:06:38.279 --> 0:06:40.760 far part of that oval away from the Sun. 0:06:42.160 --> 0:06:44.919 So it turns out that the Earth's orbit around the 0:06:44.960 --> 0:06:49.080 Sun is not a perfect circle. It's almost a perfect circle, 0:06:49.240 --> 0:06:52.920 but not quite. It's a little bit oval shape. That 0:06:53.000 --> 0:06:56.320 means the Earth is not always going at the same speed. 0:06:56.800 --> 0:06:59.520 During the narrow parts of the oval, the Earth goes 0:06:59.600 --> 0:07:02.360 a little faster, and doing the wide parts it goes 0:07:02.440 --> 0:07:05.360 a little slower, which means the extra little bit of 0:07:05.480 --> 0:07:08.120 rotation we need to catch the Sun again at the 0:07:08.160 --> 0:07:13.200 high noon changes, so sometimes it's less than four minutes, 0:07:13.320 --> 0:07:15.400 sometimes it's more than four minutes exactly. 0:07:15.680 --> 0:07:18.360 So it's basically you know again that analogy when we 0:07:18.720 --> 0:07:20.800 saw that crazy dog when we were taking our jog 0:07:20.840 --> 0:07:22.960 in the morning. If you're jogging at a little bit 0:07:23.000 --> 0:07:25.240 faster pace, you're going to have to turn a little 0:07:25.280 --> 0:07:27.559 more to see that same object. Or if you're jogging 0:07:27.560 --> 0:07:29.480 at a slower pace, you're going to have to turn 0:07:29.520 --> 0:07:31.920 a little less to see the dog behind you. 0:07:32.240 --> 0:07:35.560 Interesting, So high noon is always high noon, but it's 0:07:35.600 --> 0:07:36.520 not always noon. 0:07:37.040 --> 0:07:40.840 Yes, it's going to happen at a little bit different time, 0:07:41.760 --> 0:07:42.200 all right. 0:07:42.280 --> 0:07:46.320 So a day is definitely not a star day, which 0:07:46.360 --> 0:07:48.280 is how much time it takes with the Earth to 0:07:48.320 --> 0:07:51.400 do a full spin, and a solar day, which is 0:07:51.440 --> 0:07:54.200 how much time passes between when the sun is at 0:07:54.240 --> 0:07:58.520 its peak in the sky, changes throughout the year. So 0:07:58.560 --> 0:08:02.320 what exactly is what we call a day? What does 0:08:02.320 --> 0:08:05.040 the official day that we use in our calendars and 0:08:05.120 --> 0:08:12.640 clocks and phones represent? So if it's always changing, how 0:08:12.680 --> 0:08:16.000 do we pick what an official day is? I wonder 0:08:16.040 --> 0:08:18.600 if what we picked us the official day will be 0:08:18.760 --> 0:08:22.040 plus exactly four minutes and minus exactly four minutes, or 0:08:22.120 --> 0:08:24.200 is it like plus two minus six Do you know 0:08:24.240 --> 0:08:24.640 what I mean? 0:08:24.840 --> 0:08:27.160 So I think in the end we chose the average day. 0:08:27.360 --> 0:08:34.480 Oh fascinating, Wow, actually, we were wrong here. What we 0:08:34.640 --> 0:08:37.920 use as the official day in our everyday lives is 0:08:37.960 --> 0:08:42.640 not the average day. It's something a little different. When 0:08:42.640 --> 0:08:45.440 we come back, we'll tackle what a day actually is 0:08:45.760 --> 0:08:48.200 and we'll answer why a week is made up of 0:08:48.280 --> 0:08:52.080 seven of those days. Stay with us, we'll be right 0:08:52.120 --> 0:09:07.120 back and we're back, all right. We talked about what 0:09:07.240 --> 0:09:10.680 a day actually is, and we learned a day is 0:09:10.920 --> 0:09:13.880 not really a day. It's not how long it takes 0:09:13.880 --> 0:09:16.400 to do a full revolution of the earth, and it's 0:09:16.480 --> 0:09:19.120 not the amount of time between when the sun is 0:09:19.160 --> 0:09:22.160 at its highest peak in the sky twice in a row. 0:09:22.559 --> 0:09:25.960 That time changes throughout the year. But now let's go 0:09:26.080 --> 0:09:28.840 small and look at the time units that are shorter 0:09:29.040 --> 0:09:32.280 than a day, and let's start with the hour. Have 0:09:32.360 --> 0:09:35.200 you ever wondered why there are twenty four hours in 0:09:35.240 --> 0:09:39.560 a day? Where did the hour come from? Why does 0:09:39.600 --> 0:09:42.080 the day have twenty four hours and not twenty three? 0:09:42.280 --> 0:09:44.080 Why not thirty? Why not fifty? 0:09:44.280 --> 0:09:46.880 Yeah? So where did twenty four come from? It seems 0:09:46.920 --> 0:09:50.720 like a pretty random number to us to divide something 0:09:50.800 --> 0:09:54.319 into that cycle, And it came out of wanting twelve 0:09:54.400 --> 0:09:56.440 hours in the day and twelve hours at night. This 0:09:56.559 --> 0:10:00.640 is what the Egyptians and Babylonians wanted because it's obvious 0:10:00.679 --> 0:10:02.640 if you count on your fingers, you count to twelve. 0:10:02.880 --> 0:10:06.440 Right, Wait, how many fingers do you have? 0:10:06.520 --> 0:10:11.320 Man, So it's not that the Babylonians had extra fingers. 0:10:11.679 --> 0:10:14.920 It's basically a different way of counting, and you actually 0:10:14.960 --> 0:10:17.840 can count higher if you use your hands in this 0:10:17.920 --> 0:10:20.359 way that you count on your knuckles. 0:10:20.720 --> 0:10:21.360 Uh huh. 0:10:21.400 --> 0:10:24.160 So each finger has three knuckles, right, and so you 0:10:24.200 --> 0:10:26.280 do that for your four fingers, and you can count 0:10:26.280 --> 0:10:26.960 with your thumb. 0:10:28.160 --> 0:10:30.800 Okay, this is a little hard to explain on the radio, 0:10:31.000 --> 0:10:33.680 but basically the idea is that you can count to 0:10:33.800 --> 0:10:38.160 twelve using one hand. This is how it works. Hold 0:10:38.160 --> 0:10:41.040 your hand out so that you're looking at your palm. 0:10:41.280 --> 0:10:44.199 Now turn your thumb in so that it touches the 0:10:44.240 --> 0:10:48.840 bottom joint that connects your pinky to your hand. That's one. 0:10:49.520 --> 0:10:52.120 Then move your thumb up and touch the middle joint 0:10:52.240 --> 0:10:55.960 of your pinky. That's two. Now move it up again 0:10:56.120 --> 0:10:59.600 and touch the top joint of your pinky. That's three. 0:11:00.280 --> 0:11:02.360 Then move on to your ring finger and touch the 0:11:02.400 --> 0:11:05.439 bottom joint that connects to your ring finger to your hand, 0:11:05.920 --> 0:11:07.360 and repeat. 0:11:09.400 --> 0:11:12.920 And you go down your pinky one, two, three, go 0:11:13.000 --> 0:11:17.280 down your next finger one to three knuckles, four fingers. 0:11:17.400 --> 0:11:19.840 That adds up to twelve. So you can keep track 0:11:19.880 --> 0:11:20.840 of twelve pretty easy. 0:11:21.200 --> 0:11:22.280 Oh, I see, I see. 0:11:22.440 --> 0:11:25.480 So that was where the base twelve system came from, 0:11:25.920 --> 0:11:28.800 and so that was how everyone used to count. 0:11:29.840 --> 0:11:30.200 Really. 0:11:30.520 --> 0:11:33.800 Yeah, this idea of us counting on ten fingers is 0:11:33.920 --> 0:11:36.360 kind of a new thing that came basically from the 0:11:36.440 --> 0:11:38.760 Romans when we think, oh, it comes naturally from our 0:11:38.800 --> 0:11:41.920 ten fingers. But the original base twelve system was an 0:11:41.960 --> 0:11:44.640 easier way to count things on your hand. So this 0:11:44.760 --> 0:11:47.320 base twelve system is called the duo decimal. 0:11:47.040 --> 0:11:50.439 System, not the Dewey decimal system, yes, not. 0:11:50.400 --> 0:11:53.720 The Dewey decimal system, but the duo decimal system. 0:11:53.880 --> 0:11:55.480 So you can count to twelve with one hand. 0:11:55.840 --> 0:11:58.920 Yeah. And so this was the basis of bartering in 0:11:59.000 --> 0:12:01.640 the market or counting, you know, things that you were 0:12:01.720 --> 0:12:04.360 going to sell or whatever it might be. Started as 0:12:04.400 --> 0:12:07.480 base twelve, and so it was natural to use that 0:12:07.600 --> 0:12:10.680 system to count the hours of the day. And so 0:12:10.760 --> 0:12:14.040 they split the day into twelve hours and then split 0:12:14.080 --> 0:12:15.880 the night into twelve units. 0:12:16.120 --> 0:12:16.679 I see. 0:12:16.800 --> 0:12:19.440 And the night comes from the importance of the signs 0:12:19.480 --> 0:12:22.760 of the zodiac. There's just twelve constellations that are pretty 0:12:22.800 --> 0:12:26.400 equally spaced throughout the night sky, and so you could 0:12:26.480 --> 0:12:29.880 use these zodiac signs over the course of an evening 0:12:30.120 --> 0:12:32.600 to see how many hours you had gone. 0:12:32.760 --> 0:12:36.640 Wait what Yeah, so over the course of the night, 0:12:36.920 --> 0:12:40.280 the constellations will kind of like parade across the sky. 0:12:40.559 --> 0:12:43.400 Yeah, and so you know when this constellation set that 0:12:43.520 --> 0:12:47.319 an hour has passed. And then they decided, oh, we 0:12:47.400 --> 0:12:49.839 need a little more precision, so they broke these up 0:12:49.840 --> 0:12:52.760 into things called decans, which are a third of a 0:12:52.920 --> 0:12:56.040 zodiac sign. So they took like, ah, this star from 0:12:56.040 --> 0:12:58.400 that zodiac sign and this star from that zodiac sign 0:12:58.400 --> 0:13:01.520 of this and broke them up in threes to give 0:13:01.559 --> 0:13:03.520 them a little more accuracy over the night. 0:13:03.840 --> 0:13:07.440 I see, But wouldn't that differ depending on the season. 0:13:07.920 --> 0:13:11.120 Well, which zodiac signs are up in the night sky 0:13:11.280 --> 0:13:14.600 changes with the seasons, but not the number of them 0:13:14.600 --> 0:13:15.280 that will pass. 0:13:15.440 --> 0:13:17.880 There will always be twelve of them parading across the 0:13:17.920 --> 0:13:20.200 sky evenly space about one hour each. 0:13:20.640 --> 0:13:20.960 Yeah. 0:13:21.120 --> 0:13:25.480 Oh fascinating. And so it was like this merger of like, 0:13:25.600 --> 0:13:27.600 we like twelve because we can count with our fingers, 0:13:27.840 --> 0:13:31.320 and also there's these things, these markers in the sky. Yeah, 0:13:31.559 --> 0:13:34.880 I always thought that it was twelve because twelve have 0:13:35.000 --> 0:13:36.560 so many factors to it. 0:13:36.720 --> 0:13:38.640 Well, that was the other convenient thing of the base 0:13:38.640 --> 0:13:42.480 twelve system is you could divide by three and by four, 0:13:42.559 --> 0:13:45.800 and all these things were natural units. So three, four, 0:13:46.040 --> 0:13:48.920 there were these easily countable numbers that were the base 0:13:49.080 --> 0:13:52.160 of all these and so early mathematicians got very excited 0:13:52.200 --> 0:13:53.760 about these kind of patterns. 0:13:54.240 --> 0:13:57.080 Fascinating. So that's why we split the day into twenty 0:13:57.080 --> 0:13:57.800 four hours. 0:13:58.080 --> 0:14:01.920 Yeah, was because of the obvious counting of twelve on your. 0:14:01.840 --> 0:14:07.559 Hand, and so an hour is one twenty fourth of 0:14:07.600 --> 0:14:07.920 a day. 0:14:08.160 --> 0:14:11.920 Yeah. And why they chose to space twenty four rather 0:14:11.960 --> 0:14:14.760 than twelve, that I think was just kind of a 0:14:14.840 --> 0:14:17.560 random choice. They wanted the unit to be twelve for 0:14:17.640 --> 0:14:19.200 the day and twelve at. 0:14:19.120 --> 0:14:22.200 Night because otherwise that Keefer Sutherland show from the nineties 0:14:22.240 --> 0:14:24.640 would have been called twelve hours, not twenty four hours. Yes, 0:14:24.920 --> 0:14:27.240 all right, so then that's the hour. So the hour 0:14:27.320 --> 0:14:29.440 is dependent on what we define as a day. Yes, 0:14:31.120 --> 0:14:34.720 so that's an hour, it's one twenty fourth of a day. 0:14:34.800 --> 0:14:37.720 And now we get to minutes and seconds But first, 0:14:37.840 --> 0:14:40.120 it's interesting to think about why we would want to 0:14:40.160 --> 0:14:42.440 split the hour in the first place. 0:14:44.560 --> 0:14:48.280 As time went on, people cared about smaller and smaller 0:14:48.360 --> 0:14:52.040 time increments. Right When back in the olden days, you 0:14:52.080 --> 0:14:54.040 didn't care too much about an hour. It was just 0:14:54.080 --> 0:14:56.880 good enough to say, is it morning or afternoon? Right? 0:14:57.520 --> 0:15:00.440 But now when you had to go to work, because 0:15:00.520 --> 0:15:03.120 now there was a building that you had a job 0:15:03.200 --> 0:15:05.240 at and you had to get to that building, you 0:15:05.360 --> 0:15:07.440 needed to know roughly what hour it was. 0:15:07.640 --> 0:15:11.480 Right, because we needed to start coordinating between humans, Like 0:15:11.560 --> 0:15:13.080 I needed to know when I should go to work 0:15:13.080 --> 0:15:14.080 because you were expecting me. 0:15:14.280 --> 0:15:14.440 Right. 0:15:14.480 --> 0:15:17.880 It's like complication that comes from a society. 0:15:18.240 --> 0:15:21.400 Yeah, and so when we didn't have society, we didn't 0:15:21.400 --> 0:15:25.280 have those complications. Yeah, an hour's so complicated. You need 0:15:25.280 --> 0:15:26.920 to know everything down to the mill sector. 0:15:27.760 --> 0:15:31.640 Yeah, it's all because of people. Yes, okay, let's get 0:15:31.640 --> 0:15:35.120 to a minute. The reason the hour is split into 0:15:35.120 --> 0:15:38.520 sixty increment also goes back to counting with your hands. 0:15:38.840 --> 0:15:40.880 If you use one hand to count to twelve with 0:15:41.000 --> 0:15:43.400 your thumb and finger joints, you can use your other 0:15:43.480 --> 0:15:46.040 hand to count groups of twelve. 0:15:47.200 --> 0:15:49.120 And then you have your other hand free because you're 0:15:49.160 --> 0:15:50.560 not counting any of those fingers. 0:15:50.640 --> 0:15:51.000 Uh huh. 0:15:51.080 --> 0:15:53.080 And so then you could say, oh, I counted one twelve, 0:15:53.400 --> 0:15:55.320 I counted two twelves, I counted three twelve. 0:15:55.840 --> 0:15:59.000 Here doctor Ziegler is counting to twelve with his right hand, 0:15:59.360 --> 0:16:02.480 and each time he reaches twelve, he opens one full 0:16:02.520 --> 0:16:05.640 finger with his left hand, just like you would count 0:16:05.640 --> 0:16:07.040 to five with your fingers. 0:16:07.400 --> 0:16:10.160 It's I kind of four twelves. I counted five twelves, huh, 0:16:10.160 --> 0:16:11.560 which is sixty? Wait? 0:16:11.600 --> 0:16:13.800 Wait, so on one hand I use twelve, but on 0:16:13.840 --> 0:16:15.960 the other hand you do use your five fingers. 0:16:16.160 --> 0:16:19.600 Yeah, so you can count to twelve five times before 0:16:19.640 --> 0:16:22.080 you've used up all your fingers on both hands. 0:16:22.120 --> 0:16:24.480 But why wouldn't I use twelve times twelve? If I 0:16:24.520 --> 0:16:26.920 can count to twelve in the one hand, it's just 0:16:26.960 --> 0:16:27.360 too much. 0:16:27.480 --> 0:16:30.240 Then you have to be ambidextrious the other. 0:16:31.600 --> 0:16:33.400 So you can count to twelve with one hand, but 0:16:33.440 --> 0:16:35.720 then you keep track of how. 0:16:35.440 --> 0:16:37.680 Many twelves you count on it with the other. 0:16:37.760 --> 0:16:39.840 Other hand, which and you use your five fingers, and 0:16:39.840 --> 0:16:40.840 that's where we get sixty. 0:16:41.160 --> 0:16:46.400 Yeah. And so the natural ways of counting to Babylonian 0:16:46.600 --> 0:16:50.800 were base twelve and base sixty. So why sixty minutes 0:16:50.800 --> 0:16:53.840 to an hour was basically because we got used to 0:16:53.880 --> 0:16:56.960 this base sixty system. They decided it was sensible to 0:16:57.040 --> 0:16:59.880 use this system rather than a base twelve minutes system. 0:17:00.200 --> 0:17:02.840 Like, the word minute comes from the word sort of 0:17:03.040 --> 0:17:04.240 first first division. 0:17:04.480 --> 0:17:09.280 Yeah, first division, and then second is obviously the second division. 0:17:10.440 --> 0:17:12.560 And that's why the second is called the second. 0:17:12.840 --> 0:17:15.760 Yeah, it's because it was a first division of an 0:17:15.760 --> 0:17:17.440 hour and the second division of an hour. 0:17:18.480 --> 0:17:21.480 Man, I'm forty nine years old, and it's taking me 0:17:21.560 --> 0:17:26.480 this long to figure that, to learn this fact. Yeah, 0:17:26.680 --> 0:17:28.280 that's where the word second comes from. 0:17:28.760 --> 0:17:29.000 Yeah. 0:17:30.240 --> 0:17:33.919 Yeah, So that, according to doctor Siegler, is where the 0:17:33.960 --> 0:17:38.200 word second comes from. It's the second division of an hour. 0:17:38.760 --> 0:17:41.240 And we divide the hour and the minute into sixty 0:17:41.600 --> 0:17:45.919 because that was the preferred number system of the ancient Egyptians, 0:17:46.160 --> 0:17:49.800 except that in the nineteen sixties we decided to redefine 0:17:50.200 --> 0:17:53.680 the second, which in turn change what exactly a minute 0:17:53.800 --> 0:17:57.560 is and an hour and even a day. We'll dig 0:17:57.600 --> 0:18:00.840 into that and we'll finally answer why the week has 0:18:00.880 --> 0:18:05.600 seven days. After the break, they'll go anywhere, we'll be 0:18:05.800 --> 0:18:16.720 right back, welcome back. 0:18:17.800 --> 0:18:18.159 Okay. 0:18:18.240 --> 0:18:20.439 So the reason we have twenty four hours to a 0:18:20.560 --> 0:18:24.600 day and sixty minutes to an hour and sixty seconds 0:18:24.640 --> 0:18:28.000 to a minute. Goes back to traditions we've had since 0:18:28.160 --> 0:18:32.400 ancient Egypt, which makes you wonder why haven't we changed it. 0:18:35.200 --> 0:18:38.320 So it's a lot of just heritage and being stuck 0:18:38.400 --> 0:18:40.680 with what works. One of the reasons it's stuck in 0:18:40.720 --> 0:18:43.439 our culture is because it's always going on, right. You 0:18:43.480 --> 0:18:46.240 can't just stop and say, okay, we're all going to 0:18:46.280 --> 0:18:49.000 switch to the metric system of time. 0:18:49.119 --> 0:18:52.320 People are like, forget it, I'm too used to hours 0:18:52.320 --> 0:18:54.960 and minutes and seconds. Don't make me think too much. 0:18:55.280 --> 0:18:57.840 Yeah, And you can see that those traditions are hard 0:18:57.920 --> 0:19:01.520 to shake in even things like measurement right where we're 0:19:01.560 --> 0:19:04.200 worried in America about oh, can we ever switch to 0:19:04.240 --> 0:19:06.959 the metric system or not? But like if you switched 0:19:07.000 --> 0:19:08.600 time suddenly, now everyone's off. 0:19:10.880 --> 0:19:13.880 Okay. So for a long time, a second was a 0:19:13.920 --> 0:19:17.840 subdivision of a subdivision of a subdivision of a day, 0:19:18.359 --> 0:19:22.639 which you can measure using the average solar day. But 0:19:22.680 --> 0:19:25.480 as we said, the solar day is a bit squishy, 0:19:26.000 --> 0:19:30.200 it's not super precise. So in the nineteen sixties people 0:19:30.240 --> 0:19:33.480 decided to standardize the second and ground it in a 0:19:33.640 --> 0:19:36.080 precise physical phenomenon. 0:19:38.920 --> 0:19:42.480 So basically, by the nineteen sixties, we really were carrying 0:19:42.480 --> 0:19:46.400 about smaller time scales than the second, and we need 0:19:46.400 --> 0:19:49.719 to keep track of things really precisely. Someone in France 0:19:49.760 --> 0:19:52.960 having a different second than someone here, it just wouldn't work. 0:19:53.119 --> 0:19:55.760 So in the nineteen sixties we started carrying about these 0:19:55.800 --> 0:19:59.280 smaller units of time more precisely. So they got together 0:19:59.320 --> 0:20:01.320 internationally and said, okay, what are we going to do 0:20:01.400 --> 0:20:04.680 to develop the second? And they decided, here is this 0:20:05.040 --> 0:20:08.119 vibration that happens in the caesium atom. 0:20:08.240 --> 0:20:08.720 Uh huh. 0:20:08.720 --> 0:20:11.600 So we take this caesium atom and it turns out 0:20:11.680 --> 0:20:15.920 that nine trillion, one hundred and ninety two million, six 0:20:16.040 --> 0:20:20.639 hundred and thirty one thousand, seven hundred and seventy vibrations 0:20:20.680 --> 0:20:22.879 of the caesium atom happen every second. 0:20:23.160 --> 0:20:23.640 Huh. 0:20:23.680 --> 0:20:26.679 They said, from now on that will be the second. 0:20:26.800 --> 0:20:28.840 Whatever I was before, I forget it. This is what 0:20:28.880 --> 0:20:30.119 it is now exactly. 0:20:30.240 --> 0:20:33.960 So now the second is very precisely calibrated to this 0:20:34.160 --> 0:20:35.800 transition of the caesium. 0:20:35.400 --> 0:20:39.800 Ad why the casion atom, why not the carbon atom 0:20:39.960 --> 0:20:41.040 or oxygen atom. 0:20:41.240 --> 0:20:44.000