Why Craters Are Round, Size of Life, The Real Length of Day – TYTYK

Is there a limit to how small life can be? Or how big? Neil deGrasse Tyson and Chuck Nice break down why all craters on the moon are round, the scale to life, and why the length of the day isn’t 24 hours.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Neil deGrasse Tyson?

  Thanks for showing up for these. You know, you know, you know how I come up with them? They're like things that people know about, but they don't know as much as they think they should know or might want to know after they learned all they could know.

• 0:13Chuck Nice?

  That was very Dr. Seussian of you.

• 0:20Neil deGrasse Tyson?

  Welcome to StarTalk, your place in the universe where science and pop culture collide.

• 0:29Neil deGrasse Tyson?

  StarTalk begins right now.

• 0:35Neil deGrasse Tyson?

  Something very simple, the shape of craters.

• 0:38Chuck Nice?

  Shape of craters?

• 0:40Neil deGrasse Tyson?

  Yeah, you have to look at a picture of the moon, any photograph of the moon, what shape are the craters?

• 0:45Chuck Nice?

  Well, they're all circle, concave little circles.

• 0:48Neil deGrasse Tyson?

  They're perfect circles. Every single one of them. The big ones, the little ones, the medium ones, they are perfect circles, okay? So.

• 1:01Chuck Nice?

  Let me guess, let me guess.

• 1:04Chuck Nice?

  Aliens, just like on Earth, the same way they make the crop circles.

• 1:11Neil deGrasse Tyson?

  They make moon circles.

• 1:12Chuck Nice?

  That's how they make the moon circles.

• 1:16Neil deGrasse Tyson?

  Moon circles. So, yeah, here's the thing. It's interesting that as humans, if there's something scientists don't understand, people rapidly just go to God or aliens. Well, that's why they got the explanation for what. All right. It turned out it was a mystery why all craters are perfect circles. For the longest time. It was a mystery until about 100 years ago.

• 1:41Chuck Nice?

  Okay.

• 1:42Neil deGrasse Tyson?

  And let me tell you why it was a mystery. All right? So your first thought is, well, the moon doesn't have an atmosphere. Maybe it's getting slammed by meteors.

• 1:53Chuck Nice?

  Right.

• 1:55Neil deGrasse Tyson?

  But is every meteor coming straight down at a 90-degree angle? So that the explosion, when it hits, it makes a period? Is that, surely some of them are at an angle. You'd expect some craters to be elongated.

• 2:11Chuck Nice?

  Right.

• 2:12Neil deGrasse Tyson?

  And you'd have all sorts of shapes, from circle to very, very flattened circles. You'd expect that.

• 2:20Chuck Nice?

  Some of them would be divots. Like when you swing a golf, you know, it'd just be like a.

• 2:27Neil deGrasse Tyson?

  Oh, okay.

• 2:27Chuck Nice?

  Where it came in on the angle.

• 2:28Neil deGrasse Tyson?

  On the angle from, and with the, with the, with the, because you'd have a, the slope would be different on one side than the other.

• 2:34Chuck Nice?

  Than on the other.

• 2:35Neil deGrasse Tyson?

  Because it came, slid in.

• 2:36Chuck Nice?

  It slid in.

• 2:37Neil deGrasse Tyson?

  So you'd expect that, and it is nowhere to be found on the moon. So this energized the geologists because we know that the dark areas of the moon is where lava has once flowed. Okay?

• 2:51Chuck Nice?

  Oh, cool.

• 2:51Neil deGrasse Tyson?

  I think they call it basalt. It's dark and it's lava fields, all right? And by the way, the Apollo astronauts aimed for those places because they're flat. If you're gonna go quarter million mile and land sideways and fall over, that's it, all right? So they found the flattest areas. And those are called seas. These are, before people knew that the moon didn't have weather like we have, or oceans, these large, flat areas were called the Sea of Tranquility. Okay, that's where it gets its name.

• 3:24Chuck Nice?

  Nice.

• 3:25Neil deGrasse Tyson?

  And all the seas were named after psychological states or physiological states. So there's a Sea of Facundity. There's a Sea.

• 3:32Chuck Nice?

  All right.

• 3:33Neil deGrasse Tyson?

  Yeah, all right. So there's a, anyway, but, so they're flat because lava in liquid state flattens out, right? There you go.

• 3:40Chuck Nice?

  Okay.

• 3:40Neil deGrasse Tyson?

  All right. So wherever there was a crater, it was round. So the geologist said, it's probably not these asteroids, because they'd have to all come in perpendicular. They're probably all volcanic craters. Because volcanic craters, you punch up, it makes a hole. The hole is a circle.

• 3:57Chuck Nice?

  Right.

• 3:58Neil deGrasse Tyson?

  You know, you can, you can pull that off. So that's, that's how it stood for the longest while. Until people saw craters on top of places where it didn't look like lava had flowed.

• 4:18Chuck Nice?

  Right.

• 4:19Neil deGrasse Tyson?

  So how are you gonna have a crater and no lava signature anywhere near it? What's up with that? And so this was a conundrum, okay? I have a book from 1890. And it says, "Believed by many to be volcanic in origin, perhaps they're actually of asteroid impacts, we are not sure." Okay. It's, by the way, it was that way for most of the 20th century. Until computers came along. And you could simulate impacts.

• 4:55Chuck Nice?

  Nice.

• 4:56Neil deGrasse Tyson?

  You want to simulate it? Okay, so here you go. You ready? If you, if you have an impactor that comes in straight into a surface, it makes a circular crater. If you send it at an angle, it will make an elongated crater. Okay? This will happen. So they're saying, no, wait a minute, let's send it in faster.

• 5:18Neil deGrasse Tyson?

  Turns out, there is a magic speed with which you can send in an asteroid and on collision, it will make a perfect circle no matter the angle it hits.

• 5:33Chuck Nice?

  No matter the angle it hits.

• 5:35Neil deGrasse Tyson?

  Correct. And that speed, okay? This is, this is what, okay? You ready?

• 5:40Chuck Nice?

  Let me guess, let me guess. 88 miles per hour.

• 5:46Neil deGrasse Tyson?

  Precisely.

• 5:47Chuck Nice?

  The same speed that it takes to propel you into the future.

• 5:54Neil deGrasse Tyson?

  Because the flux capacitor.

• 5:56Chuck Nice?

  The flux capacitor.

• 6:01Neil deGrasse Tyson?

  Okay.

• 6:01Chuck Nice?

  89 miles per hour.

• 6:04Neil deGrasse Tyson?

  All right, so here's the, so here's what's going on. Let's, let's take a rock. And you can ask, why does the rock sort of hang together? Right, why isn't it just decomposed into sand? Well, because there are molecules that are attached. All right? It's molecularly attached within itself.

• 6:23Chuck Nice?

  Right.

• 6:23Neil deGrasse Tyson?

  Right, these are electromagnetic forces. You can, we know what they are. Okay.

• 6:30Neil deGrasse Tyson?

  All right? You can add up how much energy is contained in all of these molecular bonds.

• 6:37Chuck Nice?

  Okay.

• 6:37Neil deGrasse Tyson?

  And you can write down that number. And you say, this rock is held together by this much energy.

• 6:44Neil deGrasse Tyson?

  You can do that.

• 6:45Chuck Nice?

  Okay.

• 6:45Neil deGrasse Tyson?

  Okay, all right. Some rocks are held together with not much energy. Like if you take a sort of a semi, a kind of solidy thing.

• 6:53Chuck Nice?

  Like a snowball.

• 6:54Neil deGrasse Tyson?

  Well, I was gonna get to that in a minute, right?

• 6:56Chuck Nice?

  Oh, okay.

• 6:57Neil deGrasse Tyson?

  Like a sandball, right?

• 6:59Chuck Nice?

  Right.

• 7:00Neil deGrasse Tyson?

  That if you just sort of punch it, the whole thing just crumbles back into sand. But it holds its shape.

• 7:05Chuck Nice?

  It's held together.

• 7:06Neil deGrasse Tyson?

  Just for a little while. Not much energy is holding that together. Snowball, another example. Not much energy is holding, unless you like really pack it in. And what you're doing is you're melting the snow and have it refreeze, and that holds it up better. We had a whole, we had a whole explainer on the freezing and melting of ice.

• 7:24Chuck Nice?

  So what you're really doing is saying to the other person you're having the snowball fight with, "I hate you."

• 7:30Neil deGrasse Tyson?

  "I hate you even more."

• 7:32Chuck Nice?

  Even more. Because this is gonna be a nice little ice ball you're not gonna get hit in the face with.

• 7:38Neil deGrasse Tyson?

  So that held, and if it's held together only loosely, you can't even throw it without the thing flying apart, okay? So you can write down how much energy that is. Calculate it and write it down. Now, move the object through space or through the air. There's a kinetic energy it has, and this is the energy of motion. It's called kinetic energy. There's a formula. It's one-half times the mass of the object times the velocity squared. Okay? All right.

• 8:08Chuck Nice?

  Okay.

• 8:09Neil deGrasse Tyson?

  Now, the moment the kinetic energy that the object has exceeds the binding energy of the molecules.

• 8:21Chuck Nice?

  Right.

• 8:22Neil deGrasse Tyson?

  You have to ask, well, if the thing was going at that speed and then after it hits, it's going at zero speed, then what happened to all that kinetic energy? It got pumped back into the object.

• 8:37Chuck Nice?

  Right.

• 8:38Neil deGrasse Tyson?

  But that's more energy than what is holding the object together in the first place.

• 8:44Chuck Nice?

  Right.

• 8:45Neil deGrasse Tyson?

  So if you have more kinetic energy than the binding energy of the thing that has the kinetic energy.

• 8:50Chuck Nice?

  It's gonna explode.

• 8:51Neil deGrasse Tyson?

  On impact, it explodes.

• 8:54Chuck Nice?

  Wow.

• 8:56Neil deGrasse Tyson?

  So we call these high-speed collisions. And it's not just, oh, because it's going fast. No, it is higher speed than the energy that's holding it together. So on impact, it's an explosion. And explosions happen in all directions.

• 9:09Chuck Nice?

  Now, is that because the moon has no atmosphere? Because that doesn't happen on Earth.

• 9:16Neil deGrasse Tyson?

  So, so, so let's, I'll get to that in a minute.

• 9:19Chuck Nice?

  Okay.

• 9:20Neil deGrasse Tyson?

  Let me get to that. Just imagine the air is not a thing, just.

• 9:23Chuck Nice?

  Okay, imagine the air is not a thing.

• 9:24Neil deGrasse Tyson?

  Energy.

• 9:25Chuck Nice?

  You're just talking about the energy and, okay.

• 9:26Neil deGrasse Tyson?

  Okay, all right. So, so there you have it. That's the entire reason. So in fact, all the craters on the moon, damn near all the craters on them, there might be one or two that were volcanic. All the rest are asteroids, meteors coming in at whatever angle they choose.

• 9:43Chuck Nice?

  Doesn't make a difference.

• 9:45Neil deGrasse Tyson?

  That doesn't make a difference.

• 9:46Chuck Nice?

  They all explode on impact.

• 9:48Neil deGrasse Tyson?

  They explode on impact because they are coming in at, with, at what we call a high-speed collision. Now, now, let's look at snowballs. You should try this, okay? When you throw a snowball at a wall, winter's coming up, okay? We're recording this in November. So you throw it at a wall. When it hits the wall, it doesn't stay as a snowball.

• 10:13Chuck Nice?

  No, it explodes.

• 10:14Neil deGrasse Tyson?

  It basically pops.

• 10:16Chuck Nice?

  It goes everywhere.

• 10:17Neil deGrasse Tyson?

  It goes everywhere. And try this.

• 10:19Chuck Nice?

  Except for one little white dot.

• 10:20Neil deGrasse Tyson?

  Yeah, one little white dot that's stuck.

• 10:24Neil deGrasse Tyson?

  So you've done this before.

• 10:25Chuck Nice?

  Yeah, yeah.

• 10:26Neil deGrasse Tyson?

  This to all our Hawaii friends and other friends who, who don't have snowball fights. So try throwing it at different angles when winter comes. You will see that every time it explodes on impact and you see the scatter all around it in equal directions. That's because even at your speed, okay? You're not going hypersonic speeds. It's just the speed that you throw it. That's more kinetic energy than is the binding energy of the snowball.

• 10:53Chuck Nice?

  Right.

• 10:54Neil deGrasse Tyson?

  So that's why a high-speed collision, you have to ask what's binding the object and how much energy does it have of motion? And it's the, the relationship of those two numbers that'll tell you if it's a high-speed collision. So a snowball on someone's chest exploding is a high-speed collision.

• 11:11Chuck Nice?

  Nice. That's super cool.

• 11:14Neil deGrasse Tyson?

  Yeah, yeah.

• 11:15Chuck Nice?

  And so let's, let's just hope though that you never throw a snowball hard enough to leave a crater in somebody.

• 11:26Neil deGrasse Tyson?

  We still have a problem at that point. That would be more energy than is necessary to explode the the the snowball at the other side, but correct. Yeah, you don't want to be leaving craters and right. Alright, so let's get back to the atmosphere. Very important and interesting question. Okay, so now an asteroid comes and it sees the atmosphere. Right. Well, the atmosphere is going to slow it down a bit, isn't it? Okay, it's going to slow it down. If it slows it down enough, so that its kinetic energy is less than the energy that binds it together, it will survive on impact. Right.

• 12:07Neil deGrasse Tyson?

  We do find meteorites. We had the I T E after you it's on the ground meteor coming through the air, meteorite. We find there are meteorites that make it to the ground. Okay. Wow, yeah, right. We have them. They're there. Okay, they slowed down enough. Put the brakes on them. Put the brakes on them and they did not completely explode. Now, in the explosion, there could be some pieces that remain intact, just in the explosion. So meteor crater Arizona, which used to be called Barringer Crater, and Pete and geologists said, this has got to be volcanic because it's a perfect circle, but there's no volcanic activity in Arizona. Right. It's just that there's no volcano for miles. Alright, so that was a conundrum.

• 12:48Neil deGrasse Tyson?

  When we figured it out, it got renamed Meteor Crater. And those those computer simulations were were abundant in the early seventies when we were able to program computers in the science laboratories. So that that asteroid, they were saying, well, where is the asteroid? If an asteroid did it, let's dig and find the big asteroid. Alright, and so they dug and they didn't find anything because they didn't know that the sucker blew up. Okay, and so a person bought that land, a mining company bought that land on the expectation that they could mine the metals of the asteroid that must be buried deep in it, and it was nowhere to ninety percent of it vaporized on impact. There are pieces that are scattered

• 13:29Neil deGrasse Tyson?

  around and and those pieces are now in collections. We have some at the museum, but most of it is gone for that reason. And that's why craters are around. There you go. Okay, you know, we keep doing this, we'll run out of stuff to explain. That's like reaching the end of the internet, which I I don't think it's gonna happen. Well, the end of Netflix movies, right? Right. So the next.

• 14:11Neil deGrasse Tyson?

  Here's yet another fact from Lost in Space, the latest collaboration between StarTalk and National Geographic. Saturn is the only planet in the solar system whose average density is less than that of water, which means if you found a bathtub big enough, Saturn would float.

• 14:37Neil deGrasse Tyson?

  If you like that fact, you can find 4,999 more in Lost in Space. 5,000 facts to help navigate the universe. Lost in Space is now available for preorder wherever books are sold.

• 15:10Neil deGrasse Tyson?

  How long does Earth take to rotate on its axis? From what I've been told, 24 hours. 24 hours. Okay. In fact, we kind of defined 24 hours to mean that. Right. So that's how you that we divide up time. Okay, so as you might have guessed, it doesn't take 24 hours. It actually takes 23 hours, 56 minutes and 4 seconds. Okay? Really? Yes. Now, wait a minute. Wait, wait, wait, hold on. So let me just be clear about what I mean. 23 hours. Get rid of the entire just get rid of the entire solar system and watch Earth rotate. Okay, and stand there and time it. It will that spot that's in front of you will come back around in 23 hours, 56 minutes and 4 seconds.

• 15:55Neil deGrasse Tyson?

  One full revolution. Okay. Okay, that's called a sidereal day. A sidereal. Because sidereal means star, star day. So you're measuring with respect to the universe. Okay? Nice. However, we don't base our lives on when stars return to the same spot in the sky, in the night sky. We base our days on when the sun, which also happens to be a star, returns to its spot on the sky. Okay, it turns out that takes longer than 23 hours and 50. Why? I'll tell you why. Because in the time it took Earth to rotate, 23 hours

• 16:36Neil deGrasse Tyson?

  and 56 minutes, it actually moved almost one degree in its orbit around the sun. So it rotates back to where it's previously, but it has to turn a little bit extra. A little bit extra to get back to the same. A little bit extra to put the sun back in the same spot on the sky. Right. And that's a little extra minute extra. That's fantastic. And why did I say? Oh, my God, that's that's just, I love that. I've only just begun. So so that little extra four minutes. So I said, we move a degree in our orbit each day. You know, I didn't just pull that out. How many how many days are there in a year? Uh, 365. Okay, and how many degrees in a circle? 360.

• 17:21Neil deGrasse Tyson?

  Yeah, so it's about a degree a day. It's about a degree a day. Yeah, we we to technically is one degree and five 360 fifths. Oh, wow. Of a degree. But it's basically a degree a day. And in that degree, you have to turn that little extra. So just imagine you keep having to turn your head. Just a little bit more. Extra amount. Okay. Because you move just a little bit, so now you gotta look back just a little bit. Correct. That's cool. Well, let's keep going. Okay? Alright. Earth's orbit around the sun is not a perfect circle. Oh, by the way, so the first day is a sidereal day, the second day is a solar day. Gotcha. Okay, so that for obvious reasons, and they don't they're not the same. Alright, now, Earth's orbit around the sun is not a perfect circle. Right. Some, which means sometimes we're farther away, sometimes we're closer. When we are

• 18:05Neil deGrasse Tyson?

  closer, we are moving faster in our orbit than when we are farther away. Okay. Okay, that's how gravity works. So it turns out that extra four minutes is not the same if we're farther from the sun than if we're closer to the sun, because we move more than our allocated fraction of a circle when we're close to the sun and less when we're farther away from the sun. Gotcha. Okay, so the length of the solar day is changing continually throughout the year. Wow.

• 18:49Neil deGrasse Tyson?

  And sometimes it's less than 24 hours, sometimes it's more than 24 hours. So sometimes the sun gets to its highest point in the sky before clock noon. Right. And sometimes it gets, so what we do is we just average that over the whole year and say, sun, you are averaged 24 hours, and there you go. Wow. By the way, if you ever look at sundials, there's a map on the sundial that corrects for the sun being early and the sun being late. You either add or subtract up to 14 minutes of the day from what the sun time reads in order to get your clock time. Wow. Alright, every sundial has it, so it's a figure eight. It's called an analemma.

• 19:32Neil deGrasse Tyson?

  It's got a name, an analemma. But I don't want to talk about analemmas right now. So what you have on your clock is the average length of a day over the 365 days of the year. Alright, so now we define that as 24 hours, each hour 60 minutes, each minute 60 seconds. Got it. Okay. Well, what is defining this? Well, it's the rotation of the Earth. Right. Okay. Makes sense. Well, well, alright. Well, how stable is that? Even in the perfect average that we're taking? It's how, well, you'll never know, will you? Because you're using Earth to define the time for me. Right, exactly. If Earth is your measure, and you are slowing down, you will never know this.

• 20:18Neil deGrasse Tyson?

  Just there's no way to know it. Right. Okay, now, back when I was growing up, watches, they would boast, this is how old I am, they would say, get this watch, it's so accurate, it's accurate to two minutes a month. Wow, what? That that was like accurate. That is not a good advertisement. Okay, but then it was because, you know, cheap watches were 10 minutes a month. You'd have to reset, you'd set your watch every day. Why do you think heist movies would always say, let's synchronize our clocks? Right. Before they perform the heist. That's cool. They knew that the clocks there were not keeping good time. Earth was keeping the best time of them all. Okay, so now, you posed the question, maybe Earth is not

• 21:00Neil deGrasse Tyson?

  the best timekeeping device. Let's offload the responsibility of keeping time to something else, like a vibrating atom. So we did that. That sounds good. So the cesium 137, there's a electron transition between two energy levels that has a very precise frequency. Okay, very precise. You can measure. What's good about that is any lab can get some cesium and measure this and then define the length of a second in their lab. Okay? Okay. When you do this, you multiply it by 60, you multiply that by 60, you get the hour, you multiply that by 24, you do you do this and you find out that Earth is slowing down.

• 21:47Chuck Nice?

  Well, you know, it's kind of old. I'm just saying.

• 21:53Neil deGrasse Tyson?

  It's been added, it's tired.

• 21:54Chuck Nice?

  It's a long time.

• 21:55Neil deGrasse Tyson?

  It's a tired.

• 21:56Chuck Nice?

  If you're, if you're 4.6 billion years old, you might slow down a little bit too.

• 22:00Neil deGrasse Tyson?

  You might be tired too.

• 22:01Chuck Nice?

  I'm just saying, you might lose a step on your game.

• 22:03Neil deGrasse Tyson?

  That's very sweet of you, Chuck. That's very, that's very geriatrically sensitive of you. So you only would know that Earth was slowing down once you offload it to something else that tracks time.

• 22:14Chuck Nice?

  Right.

• 22:15Neil deGrasse Tyson?

  And what we found out is that the sloshing of tides on the ocean floor, on the beachfronts, actually works to slow down the rotation of the Earth.

• 22:31Chuck Nice?

  Oh, wow.

• 22:32Neil deGrasse Tyson?

  Okay, because the moon is causing these tides.

• 22:36Chuck Nice?

  Right.

• 22:36Neil deGrasse Tyson?

  Okay, and we're rotating faster than the moon is orbiting us. So the moon is tugging on tides backwards on our attempt to rotate.

• 22:47Chuck Nice?

  Right.

• 22:48Neil deGrasse Tyson?

  Okay.

• 22:49Chuck Nice?

  So it's almost like there's a, a, a counterweight.

• 22:53Neil deGrasse Tyson?

  A counterbalance, exactly.

• 22:54Chuck Nice?

  Yeah, counterbalance that's pulling against what?

• 22:56Neil deGrasse Tyson?

  Against us. So tides are slowing down the rotation of the Earth. And in response, the moon is spiraling away from us by a couple of inches a year. Okay, that's in response to Earth slowing down. It all relates to what's called the conservation of angular momentum, but it's a big ballet, okay? And so we've been slowing down and Chuck, that's, so we, what we could do is say, let's redefine the second, the length of the second, so that we always have 24 hours and 60 minutes and 60 seconds. But that's messy. Every year, here's a new definition of the second, folks. Go to your lab, redefine the CCM Adam.

• 23:34Chuck Nice?

  It's much easier to accept the fact that, you know, we're breaking up with the moon, but you know, it's just taking some time.

• 23:42Neil deGrasse Tyson?

  Breaking up is hard to do.

• 23:43Chuck Nice?

  Everybody, everybody has to be on the same pace so the breakup can be as amicable.

• 23:49Neil deGrasse Tyson?

  Ah, so that's, that's, that's, that's a nice way to think about it, yeah. So, so this, so, so we, the way we compensate for this is.

• 23:58Chuck Nice?

  How?

• 23:58Neil deGrasse Tyson?

  We add a leap second.

• 24:01Chuck Nice?

  When, when do we, oh, well, it has to be every four years then we had a.

• 24:03Neil deGrasse Tyson?

  No, no, no, no, no. Did I mention years at all? I'm talking about days, dude, days.

• 24:09Chuck Nice?

  Every four days?

• 24:10Neil deGrasse Tyson?

  No, no, no, no, no. What I'm saying is, we monitor when we have fell behind by a second.

• 24:17Chuck Nice?

  Okay, so when the second, when we know that we've lost a second, based on our atomic measurement.

• 24:23Neil deGrasse Tyson?

  Correct. Then internationally, we say, time to throw in a leap second.

• 24:27Chuck Nice?

  Now we throw it in.

• 24:28Neil deGrasse Tyson?

  By convention, we throw it in on June 30th or on December 31st. And we can throw in one at each time if we needed it, okay? Since 1973 or four, something like early 70s, there's been 23, 24 leap seconds added to the calendar.

• 24:45Chuck Nice?

  Sweet.

• 24:45Neil deGrasse Tyson?

  So when they're going to add a leap second, they choose which of those days it will be. When they do so, that final minute has 61 seconds in it.

• 24:53Chuck Nice?

  Nice.

• 24:54Neil deGrasse Tyson?

  Yes, it's very cool. It's very cool. And so, so this is what we do.

• 24:59Chuck Nice?

  The longest minute of.

• 25:01Neil deGrasse Tyson?

  Yes, it's the longest minute because it's actually 61 seconds. Okay, so newspapers like having fun with this, say, this year will be slightly longer than other years because you have to throw in the leap second. The leap second happens on Greenwich time. So for us, it would take place at like, uh, I guess 7:00 PM.

• 25:19Chuck Nice?

  Right.

• 25:19Neil deGrasse Tyson?

  Because we're five hours, uh, behind them.

• 25:22Chuck Nice?

  On the Greenwich Mean Time, right?

• 25:24Neil deGrasse Tyson?

  Greenwich Mean Time, right. So I was at a dinner party once in the June 30th leap second and 7:00 PM, that's when you're having dinner. And I said, pause. I got out the atomic clock and we just watched that sucker tick. 61 seconds went by. We toasted it with a sip of champagne and then went on our way.

• 25:41Chuck Nice?

  Okay, why are you walking around with an atomic clock?

• 25:45Neil deGrasse Tyson?

  No, no, I haven't, wait, just don't have access. Don't just, let's not, just, I got people.

• 25:51Chuck Nice?

  Okay, right on.

• 25:53Neil deGrasse Tyson?

  All right, so a couple more things. Uh, other things that can change the rotation of the Earth, not just the tidal sloshing.

• 25:59Chuck Nice?

  Right.

• 26:00Neil deGrasse Tyson?

  Okay, but here's one for you. Are you ready?

• 26:02Chuck Nice?

  Good.

• 26:03Neil deGrasse Tyson?

  Right, you've seen skaters who, uh, want to speed up their speed. So what do they do? Their hands start out extended. And they start with a slight rotation. They bring in their hands and they spin faster.

• 26:14Chuck Nice?

  Right.

• 26:14Neil deGrasse Tyson?

  Right. What they've done is they've changed where the mass is relative to their rotation axis.

• 26:20Chuck Nice?

  Right.

• 26:20Neil deGrasse Tyson?

  So the farther away the mass is, the slower they're going to rotate. The closer it is to the rotation, the faster they'll turn.

• 26:26Chuck Nice?

  Right.

• 26:26Neil deGrasse Tyson?

  Okay? If Earth has an earthquake and one of the continental slabs shifts north, okay? Then there's mass on Earth's surface that used to be closer to the equator the day before and has now moved closer to the pole. That will have the effect of speeding up the rotation of the Earth.

• 26:52Chuck Nice?

  Right.

• 26:53Neil deGrasse Tyson?

  Large animals that migrate, okay? Will change where the mass of the Earth is from the northern climes down to the south and they're farther away from the rotation of the axis.

• 27:09Neil deGrasse Tyson?

  So not only does, do tides affect the rotation of the Earth, my seasonal migration of animals affects the rotation of the Earth. And so does earthquakes, so do volcanoes and anything else that's remapping the surface of the Earth. And you know what else that's changed it? The melting of land glaciers.

• 27:27Chuck Nice?

  Uh-oh, we're in trouble.

• 27:29Neil deGrasse Tyson?

  Okay, that you got, uh, Antarctica has, has land glaciers, has and melts. What used to be right there near the pole now melts and goes closer to the equator. That will slow down the rotation of the Earth because that's like the skater bringing their hands farther away.

• 27:45Chuck Nice?

  Right.

• 27:45Neil deGrasse Tyson?

  So all of these factors combined, basically, Earth today has been increasing rather than, in principle, it could decrease depending on what's going on.

• 27:54Chuck Nice?

  Right.

• 27:55Neil deGrasse Tyson?

  Then I, I, then I had this diabolical idea. We'd go set up jet engines, um, anchor them to the Earth, face them either due east or due west and ignite them. And then the exhaust would help, uh, speed up or slow down the Earth. I thought we might do that. Then I did the math on that.

• 28:10Chuck Nice?

  And?

• 28:11Neil deGrasse Tyson?

  And no, it's not going to work. It's not enough.

• 28:16Chuck Nice?

  You would have made a good Bond villain though.

• 28:20Neil deGrasse Tyson?

  Yeah, it's just, you know, it's like Lex Luthor saying, let me, um, create an earthquake to, um.

• 28:27Chuck Nice?

  Create his front property.

• 28:28Neil deGrasse Tyson?

  Uh, in California. So yeah, it's geoengineering on a, on a huge scale. Um, but in principle, you could do that. But if you take the greatest engines and fire them, the mass of the Earth is so huge, you're just having essentially no effect.

• 28:42Chuck Nice?

  No effect at all.

• 28:43Neil deGrasse Tyson?

  Yeah. So I'm just saying, the rotation rate of the Earth is, uh, is, is susceptible to all these small effects that can add up. And we deal with it, we, you know, deal with it. We throw in leap seconds.

• 28:54Chuck Nice?

  23 hours, 56 minutes and 4 seconds.

• 29:00Neil deGrasse Tyson?

  That's our rotation rate to the stars.

• 29:02Chuck Nice?

  To the stars.

• 29:03Neil deGrasse Tyson?

  It's exactly 24 hours on average and that average is changing.

• 29:08Chuck Nice?

  Right. Oh, man, that is, that's so cool, man.

• 29:12Neil deGrasse Tyson?

  Yeah, just to show you that, that smart people think about this stuff.

• 29:15Chuck Nice?

  Yeah.

• 29:15Neil deGrasse Tyson?

  And solve it so you don't have to, because everyone, you just think everything, oh, just it works. Oh, the computer tells me what the right time is and everything and the bank knows what time it is and my GPS. We've got top people thinking about this stuff.

• 29:28Chuck Nice?

  So before the atomic clock, nobody knew what time it was.

• 29:33Neil deGrasse Tyson?

  That's why they synchronize clocks at the beginning of heist movies. Everyone had different time, dude.

• 29:40Chuck Nice?

  Oh my God, that's crazy. Oh man, I wish I lived back there and I'd never be late for anything. It'd be like, Chuck, you're 10 minutes late. Not according to my watch and as far as I could tell, don't nobody know what time it is.

• 29:59Neil deGrasse Tyson?

  I'm not 10 minutes late, you 10 minutes early.

• 30:01Chuck Nice?

  That's what the problem is.

• 30:04Neil deGrasse Tyson?

  So that's all I got to say. I mean, it's a fascinating thing.

• 30:07Chuck Nice?

  That is fascinating.

• 30:08Neil deGrasse Tyson?

  And I love thinking about it just because of how many different branches of, of the science and technological world had to come together to figure this out.

• 30:18Chuck Nice?

  Sweet. Well, I gotta go. I'm, I'm, I'm preparing for the next leap second.

• 30:26Neil deGrasse Tyson?

  So, all right, dude. And by the way, if we have a leap second announced, we'll do a special show and maybe celebrate that and I'll bring out my atomic clock and we can watch it.

• 30:34Chuck Nice?

  That'd be so cool. I'm all about it.

• 30:36Neil deGrasse Tyson?

  Okay.

• 30:37Chuck Nice?

  Yes, and make sure, don't forget the champagne because you said you had champagne the last time. So don't even try to skip out on the champagne.

• 30:43Neil deGrasse Tyson?

  Forget that.

• 30:44Chuck Nice?

  That's right. Okay, I'm just saying.

• 31:00Neil deGrasse Tyson?

  Hi, I'm Ernie Carducci from Columbus, Ohio. I'm here with my son Ernie because we listen to StarTalk every night and support StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.

• 31:24Neil deGrasse Tyson?

  Consider a few things. I want to talk about life.

• 31:28Chuck Nice?

  Well, okay.

• 31:30Neil deGrasse Tyson?

  Yeah, it's relevant. And on size and life.

• 31:36Chuck Nice?

  Well, um, listen, the way I see it is this, okay? You know, size is a preference thing, okay? And not all of us can actually, you know, be what some people might have as a preference. And, you know, why are you looking at me like that? Because why? Perhaps you've been told something about, you know, uh, my ethnicity? And maybe I'm supposed to be a certain way. Well, it doesn't necessarily happen that way for every, every person in my, in my position. And someone who looks like me.

• 32:12Neil deGrasse Tyson?

  We are, I witnessed Chuck digging himself out of a box.

• 32:18Neil deGrasse Tyson?

  So, here we go. So, you, you're in a room there, right? All right, it looks like a hotel room. All right, you can walk around on the floor.

• 32:26Chuck Nice?

  I can.

• 32:27Neil deGrasse Tyson?

  Um, if there were an ant walking around on the floor, it would be doing just what you're doing.

• 32:32Chuck Nice?

  Absolutely.

• 32:32Neil deGrasse Tyson?

  However, an ant can go to the wall and then just walk up the wall.

• 32:37Chuck Nice?

  Right.

• 32:37Neil deGrasse Tyson?

  How come you're not walking up the wall?

• 32:39Chuck Nice?

  Because I'm not Spider-Man.

• 32:40Neil deGrasse Tyson?

  Okay.

• 32:42Chuck Nice?

  That's all. If I were Spider-Man, I'd be walking up the wall.

• 32:44Neil deGrasse Tyson?

  Okay, because Spider-Man is imitating a spider.

• 32:47Chuck Nice?

  Yes, he is.

• 32:48Neil deGrasse Tyson?

  Okay, but there are no spiders the size of humans.

• 32:53Chuck Nice?

  This is true.

• 32:54Neil deGrasse Tyson?

  That can just walk up the wall.

• 32:55Chuck Nice?

  Correct.

• 32:56Neil deGrasse Tyson?

  All right, there's a reason for that. There's a very good reason for it. And it has to do with the physics of life. Nobody ever talks about it that way. People, oh, it's the biology, this. You can talk any biology you want. At the end of the day, physics sets the rules.

• 33:12Chuck Nice?

  Take that biologist.

• 33:15Chuck Nice?

  Here's a little smackdown for you, you biologist. Physics sets the rules, even in your world.

• 33:22Neil deGrasse Tyson?

  Physics. All right, so it, it all comes down to this.

• 33:27Chuck Nice?

  Go ahead.

• 33:28Neil deGrasse Tyson?

  Chuck, okay? So, um, how strong are your limbs? Well, the strength of your limbs is measured by the cross-sectional area.

• 33:42Chuck Nice?

  Oh, God.

• 33:43Neil deGrasse Tyson?

  So that tells you how big your muscles are.

• 33:45Chuck Nice?

  Well, you're just embarrassing me on every level today. First we're talking about size, now we're talking about skinny wrists. Thanks.

• 33:52Neil deGrasse Tyson?

  All right, so just take any part of your body, your legs and your arms. Take the cross-section, and that tells you how big your muscles are. And when you say have big muscles, you're measuring sort of circumference, okay?

• 34:04Chuck Nice?

  Correct, right.

• 34:05Neil deGrasse Tyson?

  And that's, that's related to the

• 34:06Chuck Nice?

  That's always the way you measure.

• 34:08Neil deGrasse Tyson?

  The circumference of the, okay.

• 34:09Chuck Nice?

  Right.

• 34:10Neil deGrasse Tyson?

  So, as you get bigger, your strength will grow as you're the area of your muscles.

• 34:20Chuck Nice?

  Right.

• 34:20Neil deGrasse Tyson?

  The cross-sectional area of your muscles.

• 34:22Chuck Nice?

  Okay.

• 34:23Neil deGrasse Tyson?

  However, your weight goes up as the cube of those dimension, dimensions.

• 34:32Chuck Nice?

  Oh, my goodness. I, now, of course, I knew your, your weight goes up, but I didn't realize it.

• 34:38Neil deGrasse Tyson?

  Okay.

• 34:39Chuck Nice?

  Wow, that's a lot.

• 34:40Neil deGrasse Tyson?

  That's, okay, so, that's why, okay? A 300-pound person does not look all that much bigger than a 200-pound person.

• 34:53Chuck Nice?

  Right.

• 34:53Neil deGrasse Tyson?

  Okay, they're chubbier and they're big, you know, if they could be tall, whatever. But if you start increasing depth, height, and width.

• 35:01Chuck Nice?

  Right.

• 35:01Neil deGrasse Tyson?

  Your volume, as your volume increases, so does your mass. But your strength necessary to sustain that volume and that weight does not go up in proportion.

• 35:14Chuck Nice?

  Right.

• 35:15Neil deGrasse Tyson?

  So, your limbs, if you're gonna hold up a heavy animal, your limbs have to be much fatter than they would otherwise be if you were smaller. And what are your heaviest animals on Earth?

• 35:30Chuck Nice?

  Uh, your elephant, your whale?

• 35:32Neil deGrasse Tyson?

  Well, yeah, on Earth's surface. The way, the, the elephant. The elephant. How, its legs are huge.

• 35:40Chuck Nice?

  Yes.

• 35:41Neil deGrasse Tyson?

  Okay, they don't have spindly legs.

• 35:43Chuck Nice?

  No, they don't.

• 35:44Neil deGrasse Tyson?

  Their legs are huge to compensate for the fact that strength only goes up as the area of their muscles. While the weight is going up as the volume. And volume rapidly outstrips area. Okay? Now, you can go the opposite direction as you get smaller and smaller and smaller. Your, the weight with your volume gets lower and lower and lower. And the strength of your limbs becomes better relative to your body weight.

• 36:15Chuck Nice?

  So why an ant can lift, what is it?

• 36:17Neil deGrasse Tyson?

  Not only is it why they can lift things relative to their body weight.

• 36:22Chuck Nice?

  Relative to the body weight.

• 36:23Neil deGrasse Tyson?

  Okay, all right. There's, not only can they do that, it's why they can get around with really skinny legs.

• 36:29Chuck Nice?

  Right.

• 36:30Neil deGrasse Tyson?

  Okay, yes, they have six of them, but they're really skinny compared to the size of, to the thickness of their body. Because the, the legs aren't holding up much weight relative to their own strength.

• 36:40Chuck Nice?

  Right, and they intermittent fast. They do intermittent fasting too, so.

• 36:44Neil deGrasse Tyson?

  How that works, thank you.

• 36:48Neil deGrasse Tyson?

  Go to an ant colony, they have these diet books.

• 36:52Chuck Nice?

  Wow, so you know what? You just, you just gave me a really, um, stark thought. Which is, I watched this documentary about this guy who climbed, uh, uh, the only cliff face that these people die all the time climbing without any ballet. And, um, this guy was super skinny.

• 37:16Neil deGrasse Tyson?

  Yep, yep.

• 37:18Chuck Nice?

  Not, not strong like with big giant muscles, but I mean, his muscles, when you look at his musculature, this dude was ripped.

• 37:27Neil deGrasse Tyson?

  He's ripped, but he doesn't weigh very much.

• 37:29Chuck Nice?

  But he doesn't weigh much at all.

• 37:30Neil deGrasse Tyson?

  Correct, correct. And that's why in the movie Cliffhanger, which involved rock climbers and mountain climbers, it starred Sylvester Stallone, who's got all these muscles, is like, no! Every mountain climber on Earth knew that that is not the body type. Because he's got muscles where he does not need them. He's got body mass that is counter to his ability to support himself.

• 37:54Chuck Nice?

  Right.

• 37:54Neil deGrasse Tyson?

  So, so the point is, generally, and there's certain exceptions depending on environments, the smaller you are, the, the, the less you weigh, the thinner your legs can be and still hold up your weight. And the bigger you are in mass, the thicker your legs are. So rhinoceruses and hippopotamuses.

• 38:14Chuck Nice?

  Right.

• 38:14Neil deGrasse Tyson?

  Hippopotami and, and elephants all have really thick legs. Because as they got bigger, uh, if they kept their thin legs, they'd break their legs. And that'd be, that's the end of you. You get eaten and that, you leave the gene pool very quickly. When, when that happens, okay?

• 38:33Chuck Nice?

  All, all the lions are missing you.

• 38:37Chuck Nice?

  Remember what we used to, remember those elephants with the skinny legs? And we, we used to just find them lying around. Oh, they made such a delicious meal.

• 38:50Chuck Nice?

  Remember, remember those days? We would just walk, walk out on the plane and we would find.

• 38:59Neil deGrasse Tyson?

  The elephants are crutches because they kept breaking their legs, right? So, anyhow, so.

• 39:05Chuck Nice?

  Oh, snap.

• 39:05Neil deGrasse Tyson?

  So that's why you, you don't find very tiny creatures with really thick legs. That's, that, so, because they don't need it. That's the point. Okay, so, so now, that, so that's a important fact number one. Whales are different because they don't weigh anything.

• 39:23Chuck Nice?

  Right.

• 39:24Neil deGrasse Tyson?

  You gotta go back to our weight density and whatever.

• 39:27Chuck Nice?

  I was just about to say.

• 39:28Neil deGrasse Tyson?

  Did we talk about, I think we talked about that.

• 39:29Chuck Nice?

  No, we didn't, but they're buoyant because they're at a certain depth and that.

• 39:33Neil deGrasse Tyson?

  Right, and so, so they don't, so they don't have to hold up their own weight. That's why they can get so big.

• 39:38Chuck Nice?

  Right.

• 39:38Neil deGrasse Tyson?

  Okay, so it doesn't, it's not fair to say, how much does that whale weigh? It weighs 400 tons. No, it doesn't. It weighs zero because it is neutrally buoyant in the water. And if you bring it onto the land, it will die because it cannot hold up its own weight. It cannot do anything in its own weight. So you cannot say it weighs that much because that's not where it lives.

• 40:00Chuck Nice?

  It makes so much sense because you've never seen a beach whale say, all right, I'm out of here.

• 40:08Chuck Nice?

  I'm good, I'm good with the land thing. I tried the beach, I tried the beach. Now I'm gonna roll myself back on it. Yeah, I'm, I'm good. I'm, you, you never saw it.

• 40:17Neil deGrasse Tyson?

  You never saw it. So that's, so they don't weigh anything, they don't have to hold up their own weight. So they're, they're really not, so everything I'm describing is sort of in the air on Earth's surface. Okay, all right, so, but I'm not done.

• 40:30Chuck Nice?

  Oh, cool.

• 40:31Neil deGrasse Tyson?

  Not only that, the laws of physics don't all manifest equally at all size scales.

• 40:38Chuck Nice?

  Interesting.

• 40:39Neil deGrasse Tyson?

  Okay, so, um, if you're gonna drink water, you'll put it in a glass and then you'll drink it like this.

• 40:47Chuck Nice?

  Right.

• 40:47Neil deGrasse Tyson?

  Why do you put it in a glass? Why don't you just sort of pour it in front of you? Well, because it'll flatten out on the table and you'll make a mess.

• 40:54Chuck Nice?

  Right.

• 40:55Neil deGrasse Tyson?

  Okay, but suppose I am an insect. Again, let's, I suppose I'm an ant. Does an ant need a vessel in which to put the water in order for it to drink? No, because water beads up. There's a bead of water that does not continue to spread. It could just walk up and suck the juice right out of the, out of the bead of water until it's gone. Okay.

• 41:18Chuck Nice?

  Nice.

• 41:19Neil deGrasse Tyson?

  Now, the producers and writers of the movie Bug's Life knew this. So when the mosquito went to the bar and ordered a drink, and what drink did the mosquito order? A Bloody Mary, of course.

• 41:38Neil deGrasse Tyson?

  Okay, so Bloody Mary.

• 41:41Chuck Nice?

  I just, I just turned it to my mother. I can't believe it.

• 41:44Neil deGrasse Tyson?

  You turned it to your parents. That's right.

• 41:46Chuck Nice?

  I turned it to my parents then. Oh my God.

• 41:49Neil deGrasse Tyson?

  Okay.

• 41:49Chuck Nice?

  Bloody Mary.

• 41:50Neil deGrasse Tyson?

  Bloody Mary, oh positive, okay? And so the bartender, which is another insect, I don't remember what kind, has a spigot, pours out a blob of Bloody Mary, and plunks it down in front of the mosquito, and it's just a ball. Okay? Held up by surface tension. Surface tension is this sort of, this imaginary film that exists on the surfaces of liquids that you have to sort of puncture that in order to fall through. But that's, that sort of film actually contains it in small enough amounts. Surface tension is not strong enough to contain a big blob of water like this because gravity wins. But when you're small enough, gravity loses against surface tension. Surface tension wins.

• 42:35Neil deGrasse Tyson?

  They plop this drop of Bloody Mary in front of the mosquito. Mosquito put in its nose, sucked it out, and then that's, that was the end of that scene. This was brilliant, and it's in that movie. It's a Pixar movie that people who knew physics and chemistry write in the script for that movie. So, different forces operate when you're small than when you are large. And so, that's why they have, there's something called, is it a Jesus spider? A water strider, sometimes called, there's a, there's one, something that's that walks on the water swiftly. And in some regions, they call it a Jesus spider, I think. Anyway, because Jesus in the Bible walked on water.

• 43:16Neil deGrasse Tyson?

  Well, except, Jesus weighs more than the surface tension would have held him up. So Jesus would have just sunk without some kind of magic, or spirit, or miracle, okay?

• 43:29Chuck Nice?

  Right, right.

• 43:30Neil deGrasse Tyson?

  Whereas, if you're small enough...

• 43:32Chuck Nice?

  Well, maybe he had just giant foam sandals.

• 43:35Neil deGrasse Tyson?

  Foam sandals. We didn't check.

• 43:37Chuck Nice?

  Right, he was the first person to wear the giant foam sandals. And they're just like, oh my God, Jesus, it's a miracle.

• 43:45Neil deGrasse Tyson?

  People misinterpreted it, right?

• 43:46Chuck Nice?

  Right, they were like, hey, but go ahead.

• 43:48Neil deGrasse Tyson?

  So, so with the, so all I'm saying is that if you're small enough, that surface tension, you don't weigh enough to break the surface tension. So then you can just sort of walk on the water as some insects do. So my point is, size is everything in this world. And, you might say, well, could you have something really big? Like, a life form the size of a galaxy? Probably not. Here's why. Because suppose, you're that big, by the way, the galaxy's 100,000 light years across. Suppose, you, you have, your head itches. And then you send the signal to the brain, and then it goes to your finger, and you gotta bring your finger up to scratch your head.

• 44:33Chuck Nice?

  Well, that, that took, that took about 30 million years.

• 44:37Neil deGrasse Tyson?

  It took...

• 44:40Neil deGrasse Tyson?

  It's gonna take at least 100,000 years to get your arm to your head moving at the speed of light. And you're probably not moving at the speed of light. So, so you just, you're not gonna be able to respond to stimulus the way life needs to in order to thrive in an environment. So there's certain sizes above which are not realistic. So, physics contains the largest and the small. And by the way, you can't be so small that quantum physics prevents your molecules from, from binding. You can't be smaller than the sizes of molecules.

• 45:17Chuck Nice?

  Right.

• 45:17Neil deGrasse Tyson?

  Because, what are you at that point? Okay? If molecules comprise life, you can't be life-size smaller than a molecule. It's just not, there's no, so, so the chemistry and physics contain all the realms in which you will find biology. And that's just the beginning of it. I'm giving you the basics of it. Where, where, that's the entry level, sort of size and life 101. Uh, so, so there you have it. So, so Spider-Man, he's got the powers of a spider? No, not if he's that size. He doesn't.

• 45:50Chuck Nice?

  No, he doesn't.

• 45:51Neil deGrasse Tyson?

  No, he doesn't.

• 45:52Chuck Nice?

  Right.

• 45:52Neil deGrasse Tyson?

  No, he doesn't. He can't. No.

• 45:56Chuck Nice?

  He basically just has the powers of a really, really good rock climber.

• 46:00Neil deGrasse Tyson?

  Rock climber.

• 46:05Neil deGrasse Tyson?

  Yes.

• 46:06Chuck Nice?

  That's about it.

• 46:07Neil deGrasse Tyson?

  That, that's about it. All right, we gotta, we gotta go there.

• 46:11Chuck Nice?

  All righty.

• 46:11Neil deGrasse Tyson?

  Good to have you.

• 46:12Chuck Nice?

  Always a pleasure.

• 46:13Neil deGrasse Tyson?

  Neil deGrasse Tyson, signing off, bidding you. Keep looking out.