1 00:00:01,160 --> 00:00:04,760 Speaker 1: Hey, welcome to Sign Stuff, a production of iHeartRadio. I'm 2 00:00:04,760 --> 00:00:07,800 Speaker 1: hoorheit him and today we're asking the question why does 3 00:00:07,880 --> 00:00:12,200 Speaker 1: the week have seven days? Why not six days or nine? 4 00:00:12,760 --> 00:00:15,240 Speaker 1: It's part of a larger episode in which we explore 5 00:00:15,480 --> 00:00:18,760 Speaker 1: the signs behind the time units we use in our 6 00:00:18,800 --> 00:00:22,320 Speaker 1: everyday lives. For example, we're gonna answer the question why 7 00:00:22,400 --> 00:00:26,000 Speaker 1: is a second called a second? Or is it day 8 00:00:26,239 --> 00:00:30,040 Speaker 1: actually one full rotation of the Earth. As we'll learn, 9 00:00:30,200 --> 00:00:32,400 Speaker 1: there are all kinds of surprises in the way we 10 00:00:32,479 --> 00:00:35,760 Speaker 1: keep track of time. So set your clocks, take a 11 00:00:35,840 --> 00:00:39,240 Speaker 1: minute with us, because the hour has come to answer 12 00:00:39,280 --> 00:00:50,880 Speaker 1: the question why does the week have seven days? Hi? Everyone, 13 00:00:51,159 --> 00:00:54,160 Speaker 1: Today we're going to explore the signs behind the time 14 00:00:54,280 --> 00:00:57,440 Speaker 1: units we use in our everyday lives. We're gonna learn 15 00:00:57,480 --> 00:01:01,040 Speaker 1: things like why does a minute have sixty second? Or 16 00:01:01,080 --> 00:01:03,080 Speaker 1: why are there twelve months to a year? 17 00:01:03,760 --> 00:01:03,960 Speaker 2: Now? 18 00:01:04,000 --> 00:01:06,120 Speaker 1: As it turns out, a lot of time units we 19 00:01:06,240 --> 00:01:10,000 Speaker 1: use have their origin in the movement of celestial bodies 20 00:01:10,040 --> 00:01:12,800 Speaker 1: in space, which is why our guide for today is 21 00:01:12,800 --> 00:01:16,960 Speaker 1: my friend, Professor Matt Siegler, a planetary scientist at the 22 00:01:17,080 --> 00:01:21,560 Speaker 1: University of Hawaii. Here's what he does. Well, Thank you, 23 00:01:21,600 --> 00:01:22,840 Speaker 1: doctor Siegler for joining us. 24 00:01:23,120 --> 00:01:25,720 Speaker 2: Thank you for having me. My name is Matt Siegler. 25 00:01:25,800 --> 00:01:30,479 Speaker 2: I'm a professor at University Hawaii and I studied planets. 26 00:01:30,720 --> 00:01:34,039 Speaker 2: So I work on about ten different spacecraft missions that 27 00:01:34,080 --> 00:01:38,160 Speaker 2: are going to the Moon or Mars or Jupiter's moons. 28 00:01:38,200 --> 00:01:40,680 Speaker 1: So you based out of Hawaii, but you work with NASA, 29 00:01:40,720 --> 00:01:42,080 Speaker 1: and yeah. 30 00:01:41,760 --> 00:01:44,880 Speaker 2: So most projects are going to be through NASA projects. 31 00:01:45,040 --> 00:01:48,280 Speaker 2: And then I'm working on the Canadian rover that's going 32 00:01:48,360 --> 00:01:50,840 Speaker 2: to the south pole of the Moon and roughly twenty 33 00:01:50,880 --> 00:01:54,840 Speaker 2: twenty seven, and occasionally I've worked with some ISSA missions. Uh. 34 00:01:55,040 --> 00:01:59,200 Speaker 1: Interesting, in ISSA means what ISSA is European Space Agency. Well, 35 00:01:59,240 --> 00:02:01,320 Speaker 1: the reason I thought you for this topic was that 36 00:02:01,480 --> 00:02:06,320 Speaker 1: you're expert on planets, and I imagine that time is 37 00:02:06,440 --> 00:02:09,000 Speaker 1: very important when you're thinking about the different planets, Like 38 00:02:09,040 --> 00:02:11,080 Speaker 1: you have to think about how long the rotation of 39 00:02:11,120 --> 00:02:14,000 Speaker 1: Mars takes or how long does the Moon go around 40 00:02:14,040 --> 00:02:15,840 Speaker 1: the Earth to be able to talk to it right. 41 00:02:16,040 --> 00:02:19,280 Speaker 2: Oh, yeah, your spacecraft might be orbiting at a certain 42 00:02:19,360 --> 00:02:21,920 Speaker 2: rate around the Moon or you might be landed on 43 00:02:21,960 --> 00:02:23,880 Speaker 2: the Moon or Mars, and then you need to care 44 00:02:23,919 --> 00:02:26,760 Speaker 2: about what the day night cycle is. But then also 45 00:02:26,840 --> 00:02:29,840 Speaker 2: you're thinking about, you know, when Will has come to 46 00:02:29,919 --> 00:02:32,239 Speaker 2: view of Earth and when we'll be able to talk 47 00:02:32,280 --> 00:02:35,200 Speaker 2: to it, or maybe you're waiting for a satellite that's 48 00:02:35,200 --> 00:02:37,480 Speaker 2: going around Mars to come overhead that you talk to. 49 00:02:37,639 --> 00:02:38,000 Speaker 1: It's. 50 00:02:38,240 --> 00:02:42,639 Speaker 2: Yeah, there's a lot of complicated timekeeping, all right. 51 00:02:42,720 --> 00:02:45,280 Speaker 1: So the first unit of time doctor Siegier and I 52 00:02:45,360 --> 00:02:48,960 Speaker 1: talked about was the day. Most people think that a 53 00:02:49,080 --> 00:02:51,480 Speaker 1: day is how much time it takes for the Earth 54 00:02:51,680 --> 00:02:55,239 Speaker 1: to spin and do a full rotation, but actually that's 55 00:02:55,280 --> 00:03:00,920 Speaker 1: not really true. Let's start with the day. Why did 56 00:03:00,960 --> 00:03:01,880 Speaker 1: you want to start with the day? 57 00:03:02,040 --> 00:03:04,600 Speaker 2: So the day is kind of an obvious place to start, 58 00:03:04,680 --> 00:03:07,480 Speaker 2: because that is the most simple thing of you look 59 00:03:07,520 --> 00:03:09,880 Speaker 2: at the sun and you wanted to come back to 60 00:03:09,960 --> 00:03:13,040 Speaker 2: noon the next day, Right, that will happen in a 61 00:03:13,040 --> 00:03:16,440 Speaker 2: certain amount of time. But early on we realized that 62 00:03:16,440 --> 00:03:18,560 Speaker 2: that was actually different than if you looked at a 63 00:03:18,639 --> 00:03:22,160 Speaker 2: star and wanted that star to come back overhead. Those 64 00:03:22,200 --> 00:03:24,360 Speaker 2: two things were just a little bit different. 65 00:03:25,680 --> 00:03:28,520 Speaker 1: Okay, so it turns out there are actually two days 66 00:03:28,600 --> 00:03:31,200 Speaker 1: here on Earth. The first is the time it takes 67 00:03:31,240 --> 00:03:33,840 Speaker 1: with the Earth to do a full rotation as it 68 00:03:33,840 --> 00:03:37,680 Speaker 1: spends relative to stay. The rest of the universe. That's 69 00:03:37,720 --> 00:03:41,000 Speaker 1: called this ideial day or the star day. And then 70 00:03:41,040 --> 00:03:42,920 Speaker 1: there's a time it takes for us to see the 71 00:03:42,960 --> 00:03:47,400 Speaker 1: Sun at its highest position or high noon. Those two 72 00:03:47,400 --> 00:03:51,800 Speaker 1: are different because the Earth is moving around the Sun. 73 00:03:54,160 --> 00:03:56,920 Speaker 2: Those are a little different. And you have to imagine 74 00:03:57,040 --> 00:04:00,600 Speaker 2: how the system works. If you're spinning around on the Earth. 75 00:04:00,760 --> 00:04:01,200 Speaker 1: Uh huh. 76 00:04:01,240 --> 00:04:04,360 Speaker 2: If you're just the Earth spinning, it actually takes twenty 77 00:04:04,360 --> 00:04:07,840 Speaker 2: three hours and fifty six minutes roughly for you to 78 00:04:07,880 --> 00:04:10,520 Speaker 2: get back to the same place. The Earth spins on 79 00:04:10,600 --> 00:04:13,720 Speaker 2: its axis once every twenty three hours and fifty six minutes. 80 00:04:13,880 --> 00:04:18,440 Speaker 2: What yeah, what, And it's the fact that we're moving 81 00:04:18,640 --> 00:04:22,240 Speaker 2: around the Sun. It takes a little bit longer each 82 00:04:22,360 --> 00:04:24,880 Speaker 2: day for us to point back at the Sun again. 83 00:04:25,400 --> 00:04:28,920 Speaker 2: And so here's this combination of the Earth's motion around 84 00:04:29,000 --> 00:04:32,080 Speaker 2: the Sun and the spinning of the Earth that come 85 00:04:32,160 --> 00:04:34,479 Speaker 2: together to give us a day which is just the 86 00:04:34,560 --> 00:04:36,840 Speaker 2: solar day, which is a little bit longer than how 87 00:04:36,880 --> 00:04:38,120 Speaker 2: long it takes for us to spin. 88 00:04:38,600 --> 00:04:40,960 Speaker 1: What wait wait wait, wait wait wait wait, you just 89 00:04:41,000 --> 00:04:44,400 Speaker 1: blew my mind and we just started this is crazy 90 00:04:44,680 --> 00:04:45,919 Speaker 1: wait wait. 91 00:04:46,120 --> 00:04:47,920 Speaker 2: Yeah, we really need one of your animations. 92 00:04:49,800 --> 00:04:54,560 Speaker 1: This is where being a cartoonist is extra frustrating. Okay, 93 00:04:54,640 --> 00:04:58,320 Speaker 1: here's what's going on to Earth actually takes twenty three 94 00:04:58,400 --> 00:05:02,359 Speaker 1: hours and fifty six minutes to spin around on its axis. 95 00:05:02,880 --> 00:05:05,599 Speaker 1: But because we're also going around the Sun, by the 96 00:05:05,640 --> 00:05:08,719 Speaker 1: time we spin around, the Sun is now a little 97 00:05:08,720 --> 00:05:11,280 Speaker 1: bit behind us, and so it takes a little bit 98 00:05:11,279 --> 00:05:14,799 Speaker 1: of extra time to catch it again at high noon. 99 00:05:16,680 --> 00:05:19,919 Speaker 2: And so because at the same time, we move a 100 00:05:19,920 --> 00:05:22,680 Speaker 2: little way around the Sun, roughly a degree or so, 101 00:05:23,080 --> 00:05:25,640 Speaker 2: it takes a little bit of extra time for us 102 00:05:25,680 --> 00:05:28,839 Speaker 2: to come back and point to the Sun because we've 103 00:05:28,880 --> 00:05:31,840 Speaker 2: moved a little ways around, And so that extra time 104 00:05:32,000 --> 00:05:34,599 Speaker 2: is four minutes every day, no. 105 00:05:34,720 --> 00:05:36,680 Speaker 1: Kidding, Wait, I guess it's sort of like the Sun 106 00:05:36,920 --> 00:05:40,920 Speaker 1: moved around relative to us in the solar system. Yeah. 107 00:05:41,040 --> 00:05:43,080 Speaker 2: So let's say you're jogging down the street and you 108 00:05:43,200 --> 00:05:45,960 Speaker 2: see a crazy looking dog or something, and you're going 109 00:05:45,960 --> 00:05:48,680 Speaker 2: to turn your head backward a little to look because 110 00:05:48,680 --> 00:05:52,640 Speaker 2: you ran past. Right. Oh, you have to turn a 111 00:05:52,680 --> 00:05:56,240 Speaker 2: little more than if you're just standing right next to 112 00:05:56,279 --> 00:05:56,760 Speaker 2: that dog. 113 00:05:57,040 --> 00:05:58,680 Speaker 1: I see, So we have to turn a little bit 114 00:05:58,680 --> 00:06:02,800 Speaker 1: more to complete the noon cycle. Yeah, and it's four minutes. 115 00:06:02,920 --> 00:06:04,120 Speaker 1: That seems like a lot. 116 00:06:04,040 --> 00:06:07,240 Speaker 2: I know, and that's basically based on the ratio between 117 00:06:07,520 --> 00:06:11,000 Speaker 2: the day and the year. But it gets even crazier. 118 00:06:12,040 --> 00:06:15,440 Speaker 1: Yes, it gets crazier. Not only is a day not 119 00:06:15,680 --> 00:06:18,520 Speaker 1: really a day, but it also depends on what time 120 00:06:18,560 --> 00:06:20,000 Speaker 1: of the year it is. 121 00:06:21,760 --> 00:06:23,680 Speaker 2: Kepler was the one that did most of the math 122 00:06:23,760 --> 00:06:26,960 Speaker 2: behind it, and he figured out that the Earth's orbit 123 00:06:27,400 --> 00:06:30,200 Speaker 2: is not a perfect circle. So this adds an extra 124 00:06:30,240 --> 00:06:33,000 Speaker 2: complication of this. When we're going around the Sun, you 125 00:06:33,279 --> 00:06:36,280 Speaker 2: go at a little bit different speeds depending on if 126 00:06:36,320 --> 00:06:38,200 Speaker 2: you're at the near part of that oval or the 127 00:06:38,279 --> 00:06:40,760 Speaker 2: far part of that oval away from the Sun. 128 00:06:42,160 --> 00:06:44,919 Speaker 1: So it turns out that the Earth's orbit around the 129 00:06:44,960 --> 00:06:49,080 Speaker 1: Sun is not a perfect circle. It's almost a perfect circle, 130 00:06:49,240 --> 00:06:52,920 Speaker 1: but not quite. It's a little bit oval shape. That 131 00:06:53,000 --> 00:06:56,320 Speaker 1: means the Earth is not always going at the same speed. 132 00:06:56,800 --> 00:06:59,520 Speaker 1: During the narrow parts of the oval, the Earth goes 133 00:06:59,600 --> 00:07:02,360 Speaker 1: a little faster, and doing the wide parts it goes 134 00:07:02,440 --> 00:07:05,360 Speaker 1: a little slower, which means the extra little bit of 135 00:07:05,480 --> 00:07:08,120 Speaker 1: rotation we need to catch the Sun again at the 136 00:07:08,160 --> 00:07:13,200 Speaker 1: high noon changes, so sometimes it's less than four minutes, 137 00:07:13,320 --> 00:07:15,400 Speaker 1: sometimes it's more than four minutes exactly. 138 00:07:15,680 --> 00:07:18,360 Speaker 2: So it's basically you know again that analogy when we 139 00:07:18,720 --> 00:07:20,800 Speaker 2: saw that crazy dog when we were taking our jog 140 00:07:20,840 --> 00:07:22,960 Speaker 2: in the morning. If you're jogging at a little bit 141 00:07:23,000 --> 00:07:25,240 Speaker 2: faster pace, you're going to have to turn a little 142 00:07:25,280 --> 00:07:27,559 Speaker 2: more to see that same object. Or if you're jogging 143 00:07:27,560 --> 00:07:29,480 Speaker 2: at a slower pace, you're going to have to turn 144 00:07:29,520 --> 00:07:31,920 Speaker 2: a little less to see the dog behind you. 145 00:07:32,240 --> 00:07:35,560 Speaker 1: Interesting, So high noon is always high noon, but it's 146 00:07:35,600 --> 00:07:36,520 Speaker 1: not always noon. 147 00:07:37,040 --> 00:07:40,840 Speaker 2: Yes, it's going to happen at a little bit different time, 148 00:07:41,760 --> 00:07:42,200 Speaker 2: all right. 149 00:07:42,280 --> 00:07:46,320 Speaker 1: So a day is definitely not a star day, which 150 00:07:46,360 --> 00:07:48,280 Speaker 1: is how much time it takes with the Earth to 151 00:07:48,320 --> 00:07:51,400 Speaker 1: do a full spin, and a solar day, which is 152 00:07:51,440 --> 00:07:54,200 Speaker 1: how much time passes between when the sun is at 153 00:07:54,240 --> 00:07:58,520 Speaker 1: its peak in the sky, changes throughout the year. So 154 00:07:58,560 --> 00:08:02,320 Speaker 1: what exactly is what we call a day? What does 155 00:08:02,320 --> 00:08:05,040 Speaker 1: the official day that we use in our calendars and 156 00:08:05,120 --> 00:08:12,640 Speaker 1: clocks and phones represent? So if it's always changing, how 157 00:08:12,680 --> 00:08:16,000 Speaker 1: do we pick what an official day is? I wonder 158 00:08:16,040 --> 00:08:18,600 Speaker 1: if what we picked us the official day will be 159 00:08:18,760 --> 00:08:22,040 Speaker 1: plus exactly four minutes and minus exactly four minutes, or 160 00:08:22,120 --> 00:08:24,200 Speaker 1: is it like plus two minus six Do you know 161 00:08:24,240 --> 00:08:24,640 Speaker 1: what I mean? 162 00:08:24,840 --> 00:08:27,160 Speaker 2: So I think in the end we chose the average day. 163 00:08:27,360 --> 00:08:34,480 Speaker 1: Oh fascinating, Wow, actually, we were wrong here. What we 164 00:08:34,640 --> 00:08:37,920 Speaker 1: use as the official day in our everyday lives is 165 00:08:37,960 --> 00:08:42,640 Speaker 1: not the average day. It's something a little different. When 166 00:08:42,640 --> 00:08:45,440 Speaker 1: we come back, we'll tackle what a day actually is 167 00:08:45,760 --> 00:08:48,200 Speaker 1: and we'll answer why a week is made up of 168 00:08:48,280 --> 00:08:52,080 Speaker 1: seven of those days. Stay with us, we'll be right 169 00:08:52,120 --> 00:09:07,120 Speaker 1: back and we're back, all right. We talked about what 170 00:09:07,240 --> 00:09:10,680 Speaker 1: a day actually is, and we learned a day is 171 00:09:10,920 --> 00:09:13,880 Speaker 1: not really a day. It's not how long it takes 172 00:09:13,880 --> 00:09:16,400 Speaker 1: to do a full revolution of the earth, and it's 173 00:09:16,480 --> 00:09:19,120 Speaker 1: not the amount of time between when the sun is 174 00:09:19,160 --> 00:09:22,160 Speaker 1: at its highest peak in the sky twice in a row. 175 00:09:22,559 --> 00:09:25,960 Speaker 1: That time changes throughout the year. But now let's go 176 00:09:26,080 --> 00:09:28,840 Speaker 1: small and look at the time units that are shorter 177 00:09:29,040 --> 00:09:32,280 Speaker 1: than a day, and let's start with the hour. Have 178 00:09:32,360 --> 00:09:35,200 Speaker 1: you ever wondered why there are twenty four hours in 179 00:09:35,240 --> 00:09:39,560 Speaker 1: a day? Where did the hour come from? Why does 180 00:09:39,600 --> 00:09:42,080 Speaker 1: the day have twenty four hours and not twenty three? 181 00:09:42,280 --> 00:09:44,080 Speaker 1: Why not thirty? Why not fifty? 182 00:09:44,280 --> 00:09:46,880 Speaker 2: Yeah? So where did twenty four come from? It seems 183 00:09:46,920 --> 00:09:50,720 Speaker 2: like a pretty random number to us to divide something 184 00:09:50,800 --> 00:09:54,319 Speaker 2: into that cycle, And it came out of wanting twelve 185 00:09:54,400 --> 00:09:56,440 Speaker 2: hours in the day and twelve hours at night. This 186 00:09:56,559 --> 00:10:00,640 Speaker 2: is what the Egyptians and Babylonians wanted because it's obvious 187 00:10:00,679 --> 00:10:02,640 Speaker 2: if you count on your fingers, you count to twelve. 188 00:10:02,880 --> 00:10:06,440 Speaker 1: Right, Wait, how many fingers do you have? 189 00:10:06,520 --> 00:10:11,320 Speaker 2: Man, So it's not that the Babylonians had extra fingers. 190 00:10:11,679 --> 00:10:14,920 Speaker 2: It's basically a different way of counting, and you actually 191 00:10:14,960 --> 00:10:17,840 Speaker 2: can count higher if you use your hands in this 192 00:10:17,920 --> 00:10:20,359 Speaker 2: way that you count on your knuckles. 193 00:10:20,720 --> 00:10:21,360 Speaker 1: Uh huh. 194 00:10:21,400 --> 00:10:24,160 Speaker 2: So each finger has three knuckles, right, and so you 195 00:10:24,200 --> 00:10:26,280 Speaker 2: do that for your four fingers, and you can count 196 00:10:26,280 --> 00:10:26,960 Speaker 2: with your thumb. 197 00:10:28,160 --> 00:10:30,800 Speaker 1: Okay, this is a little hard to explain on the radio, 198 00:10:31,000 --> 00:10:33,680 Speaker 1: but basically the idea is that you can count to 199 00:10:33,800 --> 00:10:38,160 Speaker 1: twelve using one hand. This is how it works. Hold 200 00:10:38,160 --> 00:10:41,040 Speaker 1: your hand out so that you're looking at your palm. 201 00:10:41,280 --> 00:10:44,199 Speaker 1: Now turn your thumb in so that it touches the 202 00:10:44,240 --> 00:10:48,840 Speaker 1: bottom joint that connects your pinky to your hand. That's one. 203 00:10:49,520 --> 00:10:52,120 Speaker 1: Then move your thumb up and touch the middle joint 204 00:10:52,240 --> 00:10:55,960 Speaker 1: of your pinky. That's two. Now move it up again 205 00:10:56,120 --> 00:10:59,600 Speaker 1: and touch the top joint of your pinky. That's three. 206 00:11:00,280 --> 00:11:02,360 Speaker 1: Then move on to your ring finger and touch the 207 00:11:02,400 --> 00:11:05,439 Speaker 1: bottom joint that connects to your ring finger to your hand, 208 00:11:05,920 --> 00:11:07,360 Speaker 1: and repeat. 209 00:11:09,400 --> 00:11:12,920 Speaker 2: And you go down your pinky one, two, three, go 210 00:11:13,000 --> 00:11:17,280 Speaker 2: down your next finger one to three knuckles, four fingers. 211 00:11:17,400 --> 00:11:19,840 Speaker 2: That adds up to twelve. So you can keep track 212 00:11:19,880 --> 00:11:20,840 Speaker 2: of twelve pretty easy. 213 00:11:21,200 --> 00:11:22,280 Speaker 1: Oh, I see, I see. 214 00:11:22,440 --> 00:11:25,480 Speaker 2: So that was where the base twelve system came from, 215 00:11:25,920 --> 00:11:28,800 Speaker 2: and so that was how everyone used to count. 216 00:11:29,840 --> 00:11:30,200 Speaker 1: Really. 217 00:11:30,520 --> 00:11:33,800 Speaker 2: Yeah, this idea of us counting on ten fingers is 218 00:11:33,920 --> 00:11:36,360 Speaker 2: kind of a new thing that came basically from the 219 00:11:36,440 --> 00:11:38,760 Speaker 2: Romans when we think, oh, it comes naturally from our 220 00:11:38,800 --> 00:11:41,920 Speaker 2: ten fingers. But the original base twelve system was an 221 00:11:41,960 --> 00:11:44,640 Speaker 2: easier way to count things on your hand. So this 222 00:11:44,760 --> 00:11:47,320 Speaker 2: base twelve system is called the duo decimal. 223 00:11:47,040 --> 00:11:50,439 Speaker 1: System, not the Dewey decimal system, yes, not. 224 00:11:50,400 --> 00:11:53,720 Speaker 2: The Dewey decimal system, but the duo decimal system. 225 00:11:53,880 --> 00:11:55,480 Speaker 1: So you can count to twelve with one hand. 226 00:11:55,840 --> 00:11:58,920 Speaker 2: Yeah. And so this was the basis of bartering in 227 00:11:59,000 --> 00:12:01,640 Speaker 2: the market or counting, you know, things that you were 228 00:12:01,720 --> 00:12:04,360 Speaker 2: going to sell or whatever it might be. Started as 229 00:12:04,400 --> 00:12:07,480 Speaker 2: base twelve, and so it was natural to use that 230 00:12:07,600 --> 00:12:10,680 Speaker 2: system to count the hours of the day. And so 231 00:12:10,760 --> 00:12:14,040 Speaker 2: they split the day into twelve hours and then split 232 00:12:14,080 --> 00:12:15,880 Speaker 2: the night into twelve units. 233 00:12:16,120 --> 00:12:16,679 Speaker 1: I see. 234 00:12:16,800 --> 00:12:19,440 Speaker 2: And the night comes from the importance of the signs 235 00:12:19,480 --> 00:12:22,760 Speaker 2: of the zodiac. There's just twelve constellations that are pretty 236 00:12:22,800 --> 00:12:26,400 Speaker 2: equally spaced throughout the night sky, and so you could 237 00:12:26,480 --> 00:12:29,880 Speaker 2: use these zodiac signs over the course of an evening 238 00:12:30,120 --> 00:12:32,600 Speaker 2: to see how many hours you had gone. 239 00:12:32,760 --> 00:12:36,640 Speaker 1: Wait what Yeah, so over the course of the night, 240 00:12:36,920 --> 00:12:40,280 Speaker 1: the constellations will kind of like parade across the sky. 241 00:12:40,559 --> 00:12:43,400 Speaker 2: Yeah, and so you know when this constellation set that 242 00:12:43,520 --> 00:12:47,319 Speaker 2: an hour has passed. And then they decided, oh, we 243 00:12:47,400 --> 00:12:49,839 Speaker 2: need a little more precision, so they broke these up 244 00:12:49,840 --> 00:12:52,760 Speaker 2: into things called decans, which are a third of a 245 00:12:52,920 --> 00:12:56,040 Speaker 2: zodiac sign. So they took like, ah, this star from 246 00:12:56,040 --> 00:12:58,400 Speaker 2: that zodiac sign and this star from that zodiac sign 247 00:12:58,400 --> 00:13:01,520 Speaker 2: of this and broke them up in threes to give 248 00:13:01,559 --> 00:13:03,520 Speaker 2: them a little more accuracy over the night. 249 00:13:03,840 --> 00:13:07,440 Speaker 1: I see, But wouldn't that differ depending on the season. 250 00:13:07,920 --> 00:13:11,120 Speaker 2: Well, which zodiac signs are up in the night sky 251 00:13:11,280 --> 00:13:14,600 Speaker 2: changes with the seasons, but not the number of them 252 00:13:14,600 --> 00:13:15,280 Speaker 2: that will pass. 253 00:13:15,440 --> 00:13:17,880 Speaker 1: There will always be twelve of them parading across the 254 00:13:17,920 --> 00:13:20,200 Speaker 1: sky evenly space about one hour each. 255 00:13:20,640 --> 00:13:20,960 Speaker 2: Yeah. 256 00:13:21,120 --> 00:13:25,480 Speaker 1: Oh fascinating. And so it was like this merger of like, 257 00:13:25,600 --> 00:13:27,600 Speaker 1: we like twelve because we can count with our fingers, 258 00:13:27,840 --> 00:13:31,320 Speaker 1: and also there's these things, these markers in the sky. Yeah, 259 00:13:31,559 --> 00:13:34,880 Speaker 1: I always thought that it was twelve because twelve have 260 00:13:35,000 --> 00:13:36,560 Speaker 1: so many factors to it. 261 00:13:36,720 --> 00:13:38,640 Speaker 2: Well, that was the other convenient thing of the base 262 00:13:38,640 --> 00:13:42,480 Speaker 2: twelve system is you could divide by three and by four, 263 00:13:42,559 --> 00:13:45,800 Speaker 2: and all these things were natural units. So three, four, 264 00:13:46,040 --> 00:13:48,920 Speaker 2: there were these easily countable numbers that were the base 265 00:13:49,080 --> 00:13:52,160 Speaker 2: of all these and so early mathematicians got very excited 266 00:13:52,200 --> 00:13:53,760 Speaker 2: about these kind of patterns. 267 00:13:54,240 --> 00:13:57,080 Speaker 1: Fascinating. So that's why we split the day into twenty 268 00:13:57,080 --> 00:13:57,800 Speaker 1: four hours. 269 00:13:58,080 --> 00:14:01,920 Speaker 2: Yeah, was because of the obvious counting of twelve on your. 270 00:14:01,840 --> 00:14:07,559 Speaker 1: Hand, and so an hour is one twenty fourth of 271 00:14:07,600 --> 00:14:07,920 Speaker 1: a day. 272 00:14:08,160 --> 00:14:11,920 Speaker 2: Yeah. And why they chose to space twenty four rather 273 00:14:11,960 --> 00:14:14,760 Speaker 2: than twelve, that I think was just kind of a 274 00:14:14,840 --> 00:14:17,560 Speaker 2: random choice. They wanted the unit to be twelve for 275 00:14:17,640 --> 00:14:19,200 Speaker 2: the day and twelve at. 276 00:14:19,120 --> 00:14:22,200 Speaker 1: Night because otherwise that Keefer Sutherland show from the nineties 277 00:14:22,240 --> 00:14:24,640 Speaker 1: would have been called twelve hours, not twenty four hours. Yes, 278 00:14:24,920 --> 00:14:27,240 Speaker 1: all right, so then that's the hour. So the hour 279 00:14:27,320 --> 00:14:29,440 Speaker 1: is dependent on what we define as a day. Yes, 280 00:14:31,120 --> 00:14:34,720 Speaker 1: so that's an hour, it's one twenty fourth of a day. 281 00:14:34,800 --> 00:14:37,720 Speaker 1: And now we get to minutes and seconds But first, 282 00:14:37,840 --> 00:14:40,120 Speaker 1: it's interesting to think about why we would want to 283 00:14:40,160 --> 00:14:42,440 Speaker 1: split the hour in the first place. 284 00:14:44,560 --> 00:14:48,280 Speaker 2: As time went on, people cared about smaller and smaller 285 00:14:48,360 --> 00:14:52,040 Speaker 2: time increments. Right When back in the olden days, you 286 00:14:52,080 --> 00:14:54,040 Speaker 2: didn't care too much about an hour. It was just 287 00:14:54,080 --> 00:14:56,880 Speaker 2: good enough to say, is it morning or afternoon? Right? 288 00:14:57,520 --> 00:15:00,440 Speaker 2: But now when you had to go to work, because 289 00:15:00,520 --> 00:15:03,120 Speaker 2: now there was a building that you had a job 290 00:15:03,200 --> 00:15:05,240 Speaker 2: at and you had to get to that building, you 291 00:15:05,360 --> 00:15:07,440 Speaker 2: needed to know roughly what hour it was. 292 00:15:07,640 --> 00:15:11,480 Speaker 1: Right, because we needed to start coordinating between humans, Like 293 00:15:11,560 --> 00:15:13,080 Speaker 1: I needed to know when I should go to work 294 00:15:13,080 --> 00:15:14,080 Speaker 1: because you were expecting me. 295 00:15:14,280 --> 00:15:14,440 Speaker 2: Right. 296 00:15:14,480 --> 00:15:17,880 Speaker 1: It's like complication that comes from a society. 297 00:15:18,240 --> 00:15:21,400 Speaker 2: Yeah, and so when we didn't have society, we didn't 298 00:15:21,400 --> 00:15:25,280 Speaker 2: have those complications. Yeah, an hour's so complicated. You need 299 00:15:25,280 --> 00:15:26,920 Speaker 2: to know everything down to the mill sector. 300 00:15:27,760 --> 00:15:31,640 Speaker 1: Yeah, it's all because of people. Yes, okay, let's get 301 00:15:31,640 --> 00:15:35,120 Speaker 1: to a minute. The reason the hour is split into 302 00:15:35,120 --> 00:15:38,520 Speaker 1: sixty increment also goes back to counting with your hands. 303 00:15:38,840 --> 00:15:40,880 Speaker 1: If you use one hand to count to twelve with 304 00:15:41,000 --> 00:15:43,400 Speaker 1: your thumb and finger joints, you can use your other 305 00:15:43,480 --> 00:15:46,040 Speaker 1: hand to count groups of twelve. 306 00:15:47,200 --> 00:15:49,120 Speaker 2: And then you have your other hand free because you're 307 00:15:49,160 --> 00:15:50,560 Speaker 2: not counting any of those fingers. 308 00:15:50,640 --> 00:15:51,000 Speaker 1: Uh huh. 309 00:15:51,080 --> 00:15:53,080 Speaker 2: And so then you could say, oh, I counted one twelve, 310 00:15:53,400 --> 00:15:55,320 Speaker 2: I counted two twelves, I counted three twelve. 311 00:15:55,840 --> 00:15:59,000 Speaker 1: Here doctor Ziegler is counting to twelve with his right hand, 312 00:15:59,360 --> 00:16:02,480 Speaker 1: and each time he reaches twelve, he opens one full 313 00:16:02,520 --> 00:16:05,640 Speaker 1: finger with his left hand, just like you would count 314 00:16:05,640 --> 00:16:07,040 Speaker 1: to five with your fingers. 315 00:16:07,400 --> 00:16:10,160 Speaker 2: It's I kind of four twelves. I counted five twelves, huh, 316 00:16:10,160 --> 00:16:11,560 Speaker 2: which is sixty? Wait? 317 00:16:11,600 --> 00:16:13,800 Speaker 1: Wait, so on one hand I use twelve, but on 318 00:16:13,840 --> 00:16:15,960 Speaker 1: the other hand you do use your five fingers. 319 00:16:16,160 --> 00:16:19,600 Speaker 2: Yeah, so you can count to twelve five times before 320 00:16:19,640 --> 00:16:22,080 Speaker 2: you've used up all your fingers on both hands. 321 00:16:22,120 --> 00:16:24,480 Speaker 1: But why wouldn't I use twelve times twelve? If I 322 00:16:24,520 --> 00:16:26,920 Speaker 1: can count to twelve in the one hand, it's just 323 00:16:26,960 --> 00:16:27,360 Speaker 1: too much. 324 00:16:27,480 --> 00:16:30,240 Speaker 2: Then you have to be ambidextrious the other. 325 00:16:31,600 --> 00:16:33,400 Speaker 1: So you can count to twelve with one hand, but 326 00:16:33,440 --> 00:16:35,720 Speaker 1: then you keep track of how. 327 00:16:35,440 --> 00:16:37,680 Speaker 2: Many twelves you count on it with the other. 328 00:16:37,760 --> 00:16:39,840 Speaker 1: Other hand, which and you use your five fingers, and 329 00:16:39,840 --> 00:16:40,840 Speaker 1: that's where we get sixty. 330 00:16:41,160 --> 00:16:46,400 Speaker 2: Yeah. And so the natural ways of counting to Babylonian 331 00:16:46,600 --> 00:16:50,800 Speaker 2: were base twelve and base sixty. So why sixty minutes 332 00:16:50,800 --> 00:16:53,840 Speaker 2: to an hour was basically because we got used to 333 00:16:53,880 --> 00:16:56,960 Speaker 2: this base sixty system. They decided it was sensible to 334 00:16:57,040 --> 00:16:59,880 Speaker 2: use this system rather than a base twelve minutes system. 335 00:17:00,200 --> 00:17:02,840 Speaker 1: Like, the word minute comes from the word sort of 336 00:17:03,040 --> 00:17:04,240 Speaker 1: first first division. 337 00:17:04,480 --> 00:17:09,280 Speaker 2: Yeah, first division, and then second is obviously the second division. 338 00:17:10,440 --> 00:17:12,560 Speaker 1: And that's why the second is called the second. 339 00:17:12,840 --> 00:17:15,760 Speaker 2: Yeah, it's because it was a first division of an 340 00:17:15,760 --> 00:17:17,440 Speaker 2: hour and the second division of an hour. 341 00:17:18,480 --> 00:17:21,480 Speaker 1: Man, I'm forty nine years old, and it's taking me 342 00:17:21,560 --> 00:17:26,480 Speaker 1: this long to figure that, to learn this fact. Yeah, 343 00:17:26,680 --> 00:17:28,280 Speaker 1: that's where the word second comes from. 344 00:17:28,760 --> 00:17:29,000 Speaker 2: Yeah. 345 00:17:30,240 --> 00:17:33,919 Speaker 1: Yeah, So that, according to doctor Siegler, is where the 346 00:17:33,960 --> 00:17:38,200 Speaker 1: word second comes from. It's the second division of an hour. 347 00:17:38,760 --> 00:17:41,240 Speaker 1: And we divide the hour and the minute into sixty 348 00:17:41,600 --> 00:17:45,919 Speaker 1: because that was the preferred number system of the ancient Egyptians, 349 00:17:46,160 --> 00:17:49,800 Speaker 1: except that in the nineteen sixties we decided to redefine 350 00:17:50,200 --> 00:17:53,680 Speaker 1: the second, which in turn change what exactly a minute 351 00:17:53,800 --> 00:17:57,560 Speaker 1: is and an hour and even a day. We'll dig 352 00:17:57,600 --> 00:18:00,840 Speaker 1: into that and we'll finally answer why the week has 353 00:18:00,880 --> 00:18:05,600 Speaker 1: seven days. After the break, they'll go anywhere, we'll be 354 00:18:05,800 --> 00:18:16,720 Speaker 1: right back, welcome back. 355 00:18:17,800 --> 00:18:18,159 Speaker 2: Okay. 356 00:18:18,240 --> 00:18:20,439 Speaker 1: So the reason we have twenty four hours to a 357 00:18:20,560 --> 00:18:24,600 Speaker 1: day and sixty minutes to an hour and sixty seconds 358 00:18:24,640 --> 00:18:28,000 Speaker 1: to a minute. Goes back to traditions we've had since 359 00:18:28,160 --> 00:18:32,400 Speaker 1: ancient Egypt, which makes you wonder why haven't we changed it. 360 00:18:35,200 --> 00:18:38,320 Speaker 2: So it's a lot of just heritage and being stuck 361 00:18:38,400 --> 00:18:40,680 Speaker 2: with what works. One of the reasons it's stuck in 362 00:18:40,720 --> 00:18:43,439 Speaker 2: our culture is because it's always going on, right. You 363 00:18:43,480 --> 00:18:46,240 Speaker 2: can't just stop and say, okay, we're all going to 364 00:18:46,280 --> 00:18:49,000 Speaker 2: switch to the metric system of time. 365 00:18:49,119 --> 00:18:52,320 Speaker 1: People are like, forget it, I'm too used to hours 366 00:18:52,320 --> 00:18:54,960 Speaker 1: and minutes and seconds. Don't make me think too much. 367 00:18:55,280 --> 00:18:57,840 Speaker 2: Yeah, And you can see that those traditions are hard 368 00:18:57,920 --> 00:19:01,520 Speaker 2: to shake in even things like measurement right where we're 369 00:19:01,560 --> 00:19:04,200 Speaker 2: worried in America about oh, can we ever switch to 370 00:19:04,240 --> 00:19:06,959 Speaker 2: the metric system or not? But like if you switched 371 00:19:07,000 --> 00:19:08,600 Speaker 2: time suddenly, now everyone's off. 372 00:19:10,880 --> 00:19:13,880 Speaker 1: Okay. So for a long time, a second was a 373 00:19:13,920 --> 00:19:17,840 Speaker 1: subdivision of a subdivision of a subdivision of a day, 374 00:19:18,359 --> 00:19:22,639 Speaker 1: which you can measure using the average solar day. But 375 00:19:22,680 --> 00:19:25,480 Speaker 1: as we said, the solar day is a bit squishy, 376 00:19:26,000 --> 00:19:30,200 Speaker 1: it's not super precise. So in the nineteen sixties people 377 00:19:30,240 --> 00:19:33,480 Speaker 1: decided to standardize the second and ground it in a 378 00:19:33,640 --> 00:19:36,080 Speaker 1: precise physical phenomenon. 379 00:19:38,920 --> 00:19:42,480 Speaker 2: So basically, by the nineteen sixties, we really were carrying 380 00:19:42,480 --> 00:19:46,400 Speaker 2: about smaller time scales than the second, and we need 381 00:19:46,400 --> 00:19:49,719 Speaker 2: to keep track of things really precisely. Someone in France 382 00:19:49,760 --> 00:19:52,960 Speaker 2: having a different second than someone here, it just wouldn't work. 383 00:19:53,119 --> 00:19:55,760 Speaker 2: So in the nineteen sixties we started carrying about these 384 00:19:55,800 --> 00:19:59,280 Speaker 2: smaller units of time more precisely. So they got together 385 00:19:59,320 --> 00:20:01,320 Speaker 2: internationally and said, okay, what are we going to do 386 00:20:01,400 --> 00:20:04,680 Speaker 2: to develop the second? And they decided, here is this 387 00:20:05,040 --> 00:20:08,119 Speaker 2: vibration that happens in the caesium atom. 388 00:20:08,240 --> 00:20:08,720 Speaker 1: Uh huh. 389 00:20:08,720 --> 00:20:11,600 Speaker 2: So we take this caesium atom and it turns out 390 00:20:11,680 --> 00:20:15,920 Speaker 2: that nine trillion, one hundred and ninety two million, six 391 00:20:16,040 --> 00:20:20,639 Speaker 2: hundred and thirty one thousand, seven hundred and seventy vibrations 392 00:20:20,680 --> 00:20:22,879 Speaker 2: of the caesium atom happen every second. 393 00:20:23,160 --> 00:20:23,640 Speaker 1: Huh. 394 00:20:23,680 --> 00:20:26,679 Speaker 2: They said, from now on that will be the second. 395 00:20:26,800 --> 00:20:28,840 Speaker 1: Whatever I was before, I forget it. This is what 396 00:20:28,880 --> 00:20:30,119 Speaker 1: it is now exactly. 397 00:20:30,240 --> 00:20:33,960 Speaker 2: So now the second is very precisely calibrated to this 398 00:20:34,160 --> 00:20:35,800 Speaker 2: transition of the caesium. 399 00:20:35,400 --> 00:20:39,800 Speaker 1: Ad why the casion atom, why not the carbon atom 400 00:20:39,960 --> 00:20:41,040 Speaker 1: or oxygen atom. 401 00:20:41,240 --> 00:20:44,000 Speaker 2: It was just an atom that had this property of 402 00:20:44,080 --> 00:20:45,600 Speaker 2: a very regular vibration. 403 00:20:47,560 --> 00:20:50,760 Speaker 1: All right, So we redefined the second to be the 404 00:20:50,800 --> 00:20:55,240 Speaker 1: precise vibrations of a caesium atom, and this technically redefines 405 00:20:55,320 --> 00:21:01,320 Speaker 1: the minute, and the hour and even the day. Now 406 00:21:01,320 --> 00:21:04,080 Speaker 1: here's my question. If I take the second according to 407 00:21:04,119 --> 00:21:07,080 Speaker 1: the season atom I multiplied by sixty, I now get 408 00:21:07,080 --> 00:21:10,359 Speaker 1: an official minute, right, Yes. If I multiply that by sixty, 409 00:21:10,440 --> 00:21:13,560 Speaker 1: I get a new hour, which is now the official hour. Yes. 410 00:21:13,600 --> 00:21:16,160 Speaker 1: And if I multiply that by twenty four, I now 411 00:21:16,200 --> 00:21:19,480 Speaker 1: get the official day, right yeah. So now how does 412 00:21:19,560 --> 00:21:22,880 Speaker 1: that day match to the solar day that we talked 413 00:21:22,920 --> 00:21:25,760 Speaker 1: about before, Like, I wonder if it's really the average 414 00:21:25,800 --> 00:21:28,040 Speaker 1: now or fit's deviated from the average. 415 00:21:28,280 --> 00:21:31,680 Speaker 2: Yeah, so it doesn't match. Well, that gets into why 416 00:21:31,840 --> 00:21:35,360 Speaker 2: in the nineteen seventies we started adding these leap seconds 417 00:21:35,400 --> 00:21:40,600 Speaker 2: into the calendar to correct ourselves back to this caesium 418 00:21:40,800 --> 00:21:42,600 Speaker 2: atom standard of time. 419 00:21:44,119 --> 00:21:47,080 Speaker 1: Yes, you might have heard of leap years, where every 420 00:21:47,119 --> 00:21:50,520 Speaker 1: four years we add February twenty nine to the calendar 421 00:21:50,800 --> 00:21:53,480 Speaker 1: to keep us synchronized with the orbit of the Earth 422 00:21:53,640 --> 00:21:57,600 Speaker 1: around the Sun. Well, we also have leap seconds, and 423 00:21:57,640 --> 00:21:59,959 Speaker 1: that is when we add a second to the official 424 00:22:00,280 --> 00:22:05,160 Speaker 1: time of the human race, called coordinated Universal Time or UTC, 425 00:22:05,720 --> 00:22:08,800 Speaker 1: to make up the difference between the official day, which 426 00:22:08,840 --> 00:22:11,959 Speaker 1: comes from multiplying the official second that comes from the 427 00:22:11,960 --> 00:22:16,239 Speaker 1: caesium atom, and the actual solar day, which again is 428 00:22:16,240 --> 00:22:20,240 Speaker 1: the time between when the sun reaches high noon. In 429 00:22:20,320 --> 00:22:23,320 Speaker 1: nineteen seventy two, when we first realized we needed to 430 00:22:23,359 --> 00:22:27,480 Speaker 1: do this, we added ten seconds to everyone's clock, and 431 00:22:27,560 --> 00:22:30,720 Speaker 1: since then, according to the National Institute of Standards and 432 00:22:30,760 --> 00:22:34,600 Speaker 1: Technology or NIST, we've added one second to the world 433 00:22:34,680 --> 00:22:38,560 Speaker 1: clock about every year and a half. So about every 434 00:22:38,640 --> 00:22:41,320 Speaker 1: year and a half, without most of humanity knowing it, 435 00:22:41,640 --> 00:22:45,880 Speaker 1: our clocks repeat one second right at midnight on either 436 00:22:45,920 --> 00:22:51,960 Speaker 1: New Year's Eve or the end of June. But everyone 437 00:22:52,000 --> 00:22:53,480 Speaker 1: has to remember to do that, do you know what 438 00:22:53,480 --> 00:22:57,600 Speaker 1: I mean? Like that is a huge logistical burden for everybody. 439 00:22:57,760 --> 00:23:00,520 Speaker 1: Like whatever you do, just remember everyone in the world. 440 00:23:00,520 --> 00:23:03,520 Speaker 1: We need to add one second this year, not next year, 441 00:23:03,880 --> 00:23:06,959 Speaker 1: not the even before this year. We need to everyone 442 00:23:07,000 --> 00:23:07,600 Speaker 1: at a second. 443 00:23:07,720 --> 00:23:10,560 Speaker 2: Yeah, and you know, right now, at least in history, 444 00:23:10,600 --> 00:23:13,920 Speaker 2: we don't care about those super small time scales that much. 445 00:23:13,960 --> 00:23:16,960 Speaker 2: But maybe in another hundred years, being off by a 446 00:23:17,000 --> 00:23:20,000 Speaker 2: few milliseconds is going to be an issue societal, right. 447 00:23:20,160 --> 00:23:23,159 Speaker 2: It seems so messy, yeah, I mean, and it's messy 448 00:23:23,200 --> 00:23:26,680 Speaker 2: when we're trying to match this traditional system and. 449 00:23:26,720 --> 00:23:30,960 Speaker 1: To match it to like giant physical processes like the 450 00:23:31,080 --> 00:23:33,520 Speaker 1: rotation of the Earth and whether it sinks to the 451 00:23:33,920 --> 00:23:37,760 Speaker 1: orbit around the Sun. I mean, these are huge things, right, Yeah. 452 00:23:37,920 --> 00:23:40,159 Speaker 2: And so to get to the month, we start to 453 00:23:40,200 --> 00:23:44,640 Speaker 2: throw in the moon cycle, which is another bizarre excerp. 454 00:23:47,400 --> 00:23:49,640 Speaker 1: Okay, let's get to the main question we set out 455 00:23:49,640 --> 00:23:54,280 Speaker 1: to answer, which is why does the week have seven days? 456 00:23:55,600 --> 00:23:57,600 Speaker 1: What do you know about why the week has seven days? 457 00:23:57,720 --> 00:24:01,200 Speaker 2: So the original week back in ancient Egypt was actually 458 00:24:01,280 --> 00:24:03,879 Speaker 2: ten days a week, and this came from trying to 459 00:24:03,880 --> 00:24:07,199 Speaker 2: get this daily cycle to match the lunar cycle. So 460 00:24:07,240 --> 00:24:10,040 Speaker 2: the moon appears to go from it's noon that we 461 00:24:10,080 --> 00:24:12,720 Speaker 2: see the full moon to the full moon happens in 462 00:24:12,760 --> 00:24:15,280 Speaker 2: about twenty nine and a half days, Okay, And so 463 00:24:15,320 --> 00:24:17,000 Speaker 2: that was close to thirty days. 464 00:24:17,359 --> 00:24:17,720 Speaker 1: Uh huh. 465 00:24:17,720 --> 00:24:20,520 Speaker 2: So the original idea was that thirty days are important. 466 00:24:20,720 --> 00:24:23,760 Speaker 2: And then for some reason, because thirty couldn't be broken 467 00:24:23,800 --> 00:24:26,199 Speaker 2: up by twelve, they said, ah, let's break it up 468 00:24:26,240 --> 00:24:29,520 Speaker 2: into three weeks and so there were three weeks a 469 00:24:29,520 --> 00:24:33,919 Speaker 2: month that added to thirty days, and that roughly, you know, 470 00:24:34,359 --> 00:24:36,440 Speaker 2: at twelve months of thirty days, you got to three 471 00:24:36,480 --> 00:24:40,040 Speaker 2: hundred and sixty, which fit the nice base sixty system, 472 00:24:40,440 --> 00:24:43,480 Speaker 2: and that's how it was. Then you have this other 473 00:24:43,520 --> 00:24:47,960 Speaker 2: cultural tradition of the Jewish tradition and where that became 474 00:24:47,960 --> 00:24:50,879 Speaker 2: the Christian tradition of the seven days a week. 475 00:24:51,119 --> 00:24:53,160 Speaker 1: Okay, before we get to that, I feel like you're 476 00:24:53,160 --> 00:24:56,040 Speaker 1: saying like maybe the original concept of the week was 477 00:24:56,080 --> 00:24:58,560 Speaker 1: somehow related to the month, and the concept of the 478 00:24:58,600 --> 00:25:02,040 Speaker 1: month was sort of to the moon cycle. So what's 479 00:25:02,080 --> 00:25:02,720 Speaker 1: the moon cycle? 480 00:25:03,040 --> 00:25:05,520 Speaker 2: So if you look at the moon, for it to 481 00:25:05,560 --> 00:25:09,320 Speaker 2: go from full moon to full moon, that cycle is 482 00:25:09,520 --> 00:25:11,760 Speaker 2: going to be about twenty nine and a half days. 483 00:25:12,440 --> 00:25:16,320 Speaker 2: But the rotational cycle of the moon is actually different. 484 00:25:16,720 --> 00:25:19,160 Speaker 2: How often the moon goes around the Earth and gets 485 00:25:19,160 --> 00:25:21,760 Speaker 2: to the same place in the sky, uh huh is 486 00:25:21,800 --> 00:25:26,639 Speaker 2: actually different. It's like twenty seven point three days. And 487 00:25:26,720 --> 00:25:29,680 Speaker 2: so that gets really complicated as well. Do we count 488 00:25:29,720 --> 00:25:32,359 Speaker 2: where the moon comes back to the same spot or 489 00:25:32,400 --> 00:25:34,800 Speaker 2: do we count where the moon goes through its whole cycle? 490 00:25:35,000 --> 00:25:35,359 Speaker 1: Okay? 491 00:25:35,600 --> 00:25:38,160 Speaker 2: And so it was a little bit of a which month, 492 00:25:38,280 --> 00:25:42,040 Speaker 2: do you choose develop which way you want to break 493 00:25:42,080 --> 00:25:43,320 Speaker 2: that month apart into weeks? 494 00:25:44,440 --> 00:25:47,040 Speaker 1: All Right, What doctor Siegler is saying is that the 495 00:25:47,119 --> 00:25:50,040 Speaker 1: reason we have a week is to break up the month, 496 00:25:50,359 --> 00:25:53,119 Speaker 1: and the month is related to the cycle of the moon. 497 00:25:53,600 --> 00:25:56,520 Speaker 1: Except there are two moon cycles, just like there are 498 00:25:56,600 --> 00:25:59,719 Speaker 1: two day cycles. There's how long it takes for the 499 00:25:59,720 --> 00:26:02,760 Speaker 1: moon to do a full rotation around the Earth, and 500 00:26:02,800 --> 00:26:04,800 Speaker 1: there's how long it takes for the moon to go 501 00:26:04,880 --> 00:26:09,000 Speaker 1: from full moon to full moon. One it's about thirty days, 502 00:26:09,160 --> 00:26:11,840 Speaker 1: which lends itself to have a ten day week, and 503 00:26:11,920 --> 00:26:15,280 Speaker 1: the other is about twenty eight days, which lends itself 504 00:26:15,320 --> 00:26:16,680 Speaker 1: to have a seven day week. 505 00:26:18,720 --> 00:26:22,080 Speaker 2: And so you could split the month into four seven 506 00:26:22,119 --> 00:26:24,200 Speaker 2: day weeks if it was a twenty eight day month, 507 00:26:24,359 --> 00:26:27,080 Speaker 2: or you could split it into three ten day weeks 508 00:26:27,080 --> 00:26:31,200 Speaker 2: if it were a thirty day But when the Romans 509 00:26:31,280 --> 00:26:34,879 Speaker 2: had to choose, huh, they basically went with the seven 510 00:26:35,000 --> 00:26:38,919 Speaker 2: day system because that worked better with whatever traditions they 511 00:26:38,960 --> 00:26:39,640 Speaker 2: were adopting. 512 00:26:40,040 --> 00:26:42,520 Speaker 1: Well, from what I read, nobody really cared about the 513 00:26:42,560 --> 00:26:45,600 Speaker 1: week basically, like nobody really kept track of like, oh, 514 00:26:45,640 --> 00:26:48,840 Speaker 1: this important event happened on a Tuesday. But the Jewish 515 00:26:48,840 --> 00:26:51,639 Speaker 1: people obviously did back then. You know, for them, it 516 00:26:51,720 --> 00:26:54,840 Speaker 1: was a command from God not to work. And then 517 00:26:55,440 --> 00:26:57,879 Speaker 1: what historians seem to have found is that at the 518 00:26:57,920 --> 00:27:02,600 Speaker 1: same time, the Roman people had this seven day cycle 519 00:27:03,040 --> 00:27:05,600 Speaker 1: that was just based on astrology. So they looked at 520 00:27:05,640 --> 00:27:08,679 Speaker 1: the sky. They could see five planets, the Sun, and 521 00:27:08,760 --> 00:27:12,680 Speaker 1: the moon. I imagine they couldn't like really see Neptune or Urinus. 522 00:27:12,760 --> 00:27:16,600 Speaker 2: Right, yeah, those weren't discovered until late seventeen hundreds. We 523 00:27:16,680 --> 00:27:19,679 Speaker 2: found Urinus and then Neptune was even later, so. 524 00:27:19,760 --> 00:27:21,560 Speaker 1: Right, right, but the others you can see in the sky, 525 00:27:21,680 --> 00:27:24,199 Speaker 1: right yeah, So they like each God must be in 526 00:27:24,280 --> 00:27:26,560 Speaker 1: charge of the day. So that's why we have this 527 00:27:26,680 --> 00:27:29,719 Speaker 1: astrological keeping track of seven days at a time. So 528 00:27:29,880 --> 00:27:32,560 Speaker 1: then it's sort of like this nebulous process of we 529 00:27:32,600 --> 00:27:36,439 Speaker 1: sort of have this planetary astrological seven day week. The 530 00:27:36,520 --> 00:27:39,800 Speaker 1: Jewish people are keeping track every seven days, and then 531 00:27:39,880 --> 00:27:43,720 Speaker 1: Christianity adopted this Sunday as the day of worship and 532 00:27:43,800 --> 00:27:46,280 Speaker 1: so let's make it a seven day week. 533 00:27:46,480 --> 00:27:49,000 Speaker 2: So it all kind of came out of this conglomeration 534 00:27:49,080 --> 00:27:49,960 Speaker 2: of cultures. 535 00:27:50,720 --> 00:27:53,639 Speaker 1: All right, here's the basic scenario for the month. We 536 00:27:53,680 --> 00:27:56,720 Speaker 1: seem to have based it on the lunar face cycle, 537 00:27:57,080 --> 00:28:00,320 Speaker 1: the period of time between two full moons, which is 538 00:28:00,320 --> 00:28:04,000 Speaker 1: about thirty days. But for the week, we opted to 539 00:28:04,080 --> 00:28:07,639 Speaker 1: base it on a multiple of the orbital lunar cycle. 540 00:28:07,960 --> 00:28:10,280 Speaker 1: How long it takes for the moon to go around 541 00:28:10,400 --> 00:28:11,840 Speaker 1: to Earth, which. 542 00:28:11,600 --> 00:28:14,400 Speaker 2: Is twenty eight days, probably. 543 00:28:13,960 --> 00:28:17,919 Speaker 1: Because of the cultural traditions of the Jewish Sabbath and 544 00:28:18,200 --> 00:28:22,320 Speaker 1: Roman astrology, which had seven days. But here's a twist, 545 00:28:22,720 --> 00:28:24,920 Speaker 1: how long it takes for the moon to go around 546 00:28:25,000 --> 00:28:27,000 Speaker 1: the Earth has been changing. 547 00:28:29,200 --> 00:28:32,920 Speaker 2: The month wasn't always this twenty nine and a half 548 00:28:33,040 --> 00:28:35,800 Speaker 2: day cycle. We have this whole idea of the moon 549 00:28:35,920 --> 00:28:38,120 Speaker 2: formed from a giant impact with the Earth and you 550 00:28:38,280 --> 00:28:41,360 Speaker 2: form the moon. The original moon in that idea would 551 00:28:41,400 --> 00:28:43,760 Speaker 2: have had a four day month, and then due to 552 00:28:43,920 --> 00:28:46,440 Speaker 2: the interactions with tides on the Earth. Uh huh, the 553 00:28:46,480 --> 00:28:49,440 Speaker 2: moon has in the last several billion years been moving 554 00:28:49,560 --> 00:28:52,440 Speaker 2: outward towards where it is today, and the month is 555 00:28:52,480 --> 00:28:56,680 Speaker 2: slowly getting longer all the time. So this hasn't happened 556 00:28:56,720 --> 00:28:59,160 Speaker 2: over the course of human history, right in the last 557 00:28:59,160 --> 00:29:01,800 Speaker 2: million years or so that you could say humans were around. 558 00:29:01,920 --> 00:29:04,080 Speaker 2: But if you go back in the geologic record, you 559 00:29:04,120 --> 00:29:06,560 Speaker 2: can see times when the month was actually shorter. 560 00:29:06,880 --> 00:29:10,280 Speaker 1: What you mean, like, if we had lived in a 561 00:29:10,320 --> 00:29:12,800 Speaker 1: different time in the history of Earth and created the 562 00:29:12,880 --> 00:29:16,120 Speaker 1: month like a billion years ago, there would be more 563 00:29:16,240 --> 00:29:19,920 Speaker 1: months in the year exactly. Okay, So basically the reason 564 00:29:19,960 --> 00:29:22,720 Speaker 1: we have twelve months a year is that we just 565 00:29:22,800 --> 00:29:25,360 Speaker 1: happened to be living in his time in the history 566 00:29:25,400 --> 00:29:29,200 Speaker 1: of Earth, where the moon goes around the Earth twelve 567 00:29:29,240 --> 00:29:30,880 Speaker 1: times roughly a year. 568 00:29:30,880 --> 00:29:34,760 Speaker 2: Exactly, and we picked twelve rather than thirteen because twelve 569 00:29:34,880 --> 00:29:37,560 Speaker 2: was nice to count on our fingers. 570 00:29:38,360 --> 00:29:42,240 Speaker 1: And because of the month. That's how we picked the week, 571 00:29:42,360 --> 00:29:44,440 Speaker 1: because a week, if we really probably just picked it 572 00:29:44,480 --> 00:29:48,400 Speaker 1: as a division of the month. Yeah, well, there you 573 00:29:48,440 --> 00:29:52,200 Speaker 1: have it. The reason the week has seven days is 574 00:29:52,360 --> 00:29:56,080 Speaker 1: partly cultural and religious, partly due to the physics of 575 00:29:56,120 --> 00:30:00,720 Speaker 1: the Moon's orbit, and partly coincidence. If human said come 576 00:30:00,720 --> 00:30:03,760 Speaker 1: around earlier or later in the history of the Earth, 577 00:30:04,200 --> 00:30:08,640 Speaker 1: the week might have been shorter or longer. So if 578 00:30:08,680 --> 00:30:11,760 Speaker 1: you're having a long week, just think it could have 579 00:30:11,800 --> 00:30:20,160 Speaker 1: been even longer. Thanks for joining us, See you next week. Hey, 580 00:30:20,440 --> 00:30:22,400 Speaker 1: please take a second and leave us a review on 581 00:30:22,480 --> 00:30:26,040 Speaker 1: Apple Podcasts, Spotify, or wherever you listen to the podcast. 582 00:30:26,720 --> 00:30:27,240 Speaker 2: Thanks a lot. 583 00:30:28,040 --> 00:30:31,440 Speaker 1: You've been listening to Science Stuff the production of iHeartRadio, 584 00:30:32,240 --> 00:30:36,320 Speaker 1: written and produced by me Or Hitcham, edited by Rose Seguda, 585 00:30:36,560 --> 00:30:40,760 Speaker 1: executive producer Jerry Rowland, and audio engineer and mixer Casey Peckram. 586 00:30:40,880 --> 00:30:43,040 Speaker 1: And you can follow me on social media. Just search 587 00:30:43,080 --> 00:30:46,280 Speaker 1: for PhD Comics and the name of your favorite platform. 588 00:30:46,400 --> 00:30:49,320 Speaker 1: Be sure to subscribe to Sign Stuff on the iHeartRadio app, 589 00:30:49,400 --> 00:30:52,600 Speaker 1: Apple Podcasts, or wherever you get your podcasts, and please 590 00:30:52,800 --> 00:31:06,160 Speaker 1: tell your friends We'll be back next Wednesday with another episode.