Pod Insights Daniel and Kelly's Extraordinary Universe Could the Earth be at the center of the solar system? About this episode Daniel and Kelly explain the bizarre Tychonic model of the solar system, which for centuries stood as a valid theory alongside the Copernican model.
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Transcript 10,874 words · 8 speakers
Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.
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2:43 Daniel Whiteson? When and how did we learn that the sun is at the center of the solar system? And if distance and location are just relative, what does center mean anyway? There's a commonly told story about all of this, how Copernicus and Kepler overthrew geocentrism with better data and clever math. But as usual, that story is missing a lot of the fun nuance. Did you know that it wasn't just geocentrism versus heliocentrism, but that there was a third, even weirder, theory in the mix that also explained the data very nicely? And that it was shockingly recently that we were able to nail any of this down? Understanding the true history of science is super fun because it shows you how puzzles
3:27 Daniel Whiteson? are actually sorted out and how things seem obvious in hindsight. But when you're standing at the forefront of human knowledge, the path forward is very unclear. Welcome to Daniel and Kelly's Extraordinary Universe.
3:54 Kelly Weinersmith? Hello, I'm Kelly Wiener-Smith. I study parasites and space, and I'm looking forward to seeing how many different incorrect ways I can say Tycho Brahe today.
4:06 Kelly Weinersmith? That's probably one.
4:07 Daniel Whiteson? Hi, I'm Daniel. I study particles and aliens, and even though I speak Danish, I'm not going to try the correct pronunciation of Tycho Brahe's name.
4:16 Kelly Weinersmith? So that wasn't it?
4:18 Daniel Whiteson? That was not it, because that's like a Latinization of his name, which has some other Danish formulation, which I've heard Dan say, and I'm not going to try to reproduce because it uses one of those many Danish vowels that doesn't exist in English.
4:33 Kelly Weinersmith? And you said Tijo?
4:34 Daniel Whiteson? Tycho Brahe is the like-
4:36 Kelly Weinersmith? Tijo.
4:37 Daniel Whiteson? The Latinization of it. But yeah, it's very different in the actual Danish.
4:41 Kelly Weinersmith? Okay, I was closer than I think probably any of us would have guessed. So that's pretty good. All right.
4:48 Daniel Whiteson? Points today for Kelly right off the bat.
4:50 Kelly Weinersmith? Woo hoo for not being so far off. So today we're talking about sort of misconceptions about the way the universe works. And so my question for you is, and I'll be honest, mostly this is just because I want to share a funny story. My question for you is, what, what is a misconception that you have heard from a child or a misconception that you had as a child that you thought was pretty funny and you'd like to share?
5:17 Daniel Whiteson? It was shockingly recently that one of my children, I won't embarrass them by naming which one, revealed that they didn't understand that stars were distant suns.
5:27 Kelly Weinersmith? What?
5:28 Daniel Whiteson? We had a moment at the tenor table when I said, wait, you know that stars are just other suns and their jaw just dropped. Like, that was the moment they learned that. And I felt like surprised and confused and embarrassed. Like, how can my child not have known this until fairly recently? Oh, my gosh, I have failed as a parent and as an educator.
5:54 Kelly Weinersmith? What did they think they were? Like aliens shining laser pointers?
5:58 Daniel Whiteson? That was my follow up question. And they were like, you know, I just never really gave it much thought. And I was like, what are you doing with your life? You never thought about what the stars are? Oh, my gosh. And how have I failed you as a parent?
6:12 Kelly Weinersmith? A plus, A plus. So I mentioned to one of my kids, I also will not say which one, that my husband's middle name is Alexander. And they go, Alexander? That's like a name for magicians. And I was like, magicians? And she goes, yeah, like Alexander the Great.
6:33 Daniel Whiteson? Who I saw in Vegas. He was great.
6:35 Kelly Weinersmith? He was great. And I was like, Alexander the Great was like a commander who like killed a bunch of people to make one of the largest empires in history. He wasn't pulling rabbits out of a hat. He goes, what? Oh, oh, wait. And they, whichever child it was that did that, said, what? Anyway, and then I started laughing so hard I cried. And so then they started laughing so hard they cried. And we both had a really good laugh about it. And now we joke about Alexander the Great, the magician.
7:08 Daniel Whiteson? Also not the main character from Alexander and the no good, very bad, terrible day.
7:13 Kelly Weinersmith? Oh, I loved that book when I was a kid. Yeah. Another great one. Another great Alexander, but not Alexander the Great. Yeah.
7:20 Daniel Whiteson? Absolutely. And today we are trying to clear up some of your great misconceptions about the history of physics, how we figured it all out. Because you know, physics and science more broadly is not a linear step from A to B. It's multiple branching paths, dead ends and wrong ideas which persisted for centuries before we figured stuff out. And though we often tell the stories as a linear progression, obviously moving from one step to the next, it's much more interesting when you dig into the details and learn the nuance.
7:53 Kelly Weinersmith? And I feel like we often don't hear those stories because they're harder to tell, but it's a much more accurate depiction of, you know, how humans as a society work. And so we're going to try to tell that story today because we like challenges. And I started looking through our outline today and I looked at the question you sent, our extraordinary. And I have to think that maybe they're wondering what's happening to the podcast that they're listening to because the question you asked them is, could the sun orbit the earth? And maybe, maybe Kelly next week is gonna send out, how many times have you seen Bigfoot? Or how tall is Bigfoot? But I guess we'll see what they had to say.
8:35 Daniel Whiteson? That's right. Is heliocentrism a government scam?
8:38 Kelly Weinersmith? That's right. Are the lizard people running the world?
8:44 Daniel Whiteson? That's right. But there was a caveat also in the question, right? The question was, is it possible that the sun orbits the earth with all the other planets orbiting the sun? Right? An even weirder idea.
8:57 Kelly Weinersmith? Oh, you wrote that in smaller text and so I skipped it.
9:02 Daniel Whiteson? All right. So think about your mental picture of the solar system. Is it possible that the sun could be moving around the earth with all the other planets orbiting the sun? Or is that just too weird to be true? Here's what the extraordinaries had to say.
9:18 Speaker 07 I don't think so, just based on what we know about the masses of the sun, earth and other planets. I think technically the sun and earth orbit their common center of mass, but I'm not sure that might still be inside the sun. As I understand it, it's not that the sun would orbit the earth. It's that orbits are the two objects orbiting around one point. And if you were to expand this out to all of the planets in the solar system, they are all orbiting some point, which is probably inside the sun. No, I do not think it is possible that the sun orbits the earth with all of their
9:53 Speaker 03 planets orbiting the sun. I think we've had this figured out since Copernicus. Now, if the sun orbited the earth, but all the planets still orbited it, that would make Helios really upset, I would expect, and also be more than a three-body problem. No. Since motion is relative, you could describe the motions of these things in such a way, but for that to hold with all we know about gravity, the masses of these objects and star formation.
10:29 Kelly Weinersmith? Is it possible that the sun orbits the earth with all other planets orbiting the sun? I don't think so, because otherwise that would mean that the earth is the center of gravity. And if the sun orbits the earth, then all other planets will also orbit the earth. All right. So at least one of our extraordinaries are 100% on to you and provided the historical context.
10:58 Kelly Weinersmith? I think you confused some of them.
11:01 Kelly Weinersmith? And the rest of them are switching over to Real Science Podcast now, Daniel.
11:08 Daniel Whiteson? Join us next week. We'll be interviewing Bigfoot on his theory of heliocentrism.
11:15 Kelly Weinersmith? Okay, but what is, what is the context for why you asked this question in particular?
11:22 Daniel Whiteson? The context is the history of how we figured out the geometry of the solar system, and crucially, how it moves in relation to the rest of the universe. And it turns out the usual story of like, the Earth is the center of the solar system, to the Sun is the center of the solar system, and that we moved to this new idea about 500 years ago, misses a lot of interesting nuance about the history of physics and the alternative ideas, which took a long time to squash.
11:48 Kelly Weinersmith? All right. Well, let's start at the very beginning then. What was like the first theory for what was happening with the Earth and the Sun? I mean, fortunately, some people who were not your kids were looking outwards and were thinking, what's going on out there?
12:01 Daniel Whiteson? Ouch, ouch.
12:04 Kelly Weinersmith? Sorry, I won't pick on your kids anymore.
12:08 Daniel Whiteson? No, that's a blow against me as a parent. Ooh.
12:12 Daniel Whiteson? You know, if you read ancient theology and ancient writing about the solar system, people were curious about it for a long, long time, and they had sort of a mental picture of how things worked. And, you know, some of them were geometric thinkers, and they imagined the Earth as a flat disk covered in a dome, and the stars were like lights in that dome somehow. And other theories, like the Chinese, they were more arithmetic, just looking at the patterns in the sky, not always assembling like a geometric picture of like where everything was at the same time. I think the first like credible theory for how things work comes from the ancient Greeks. You know, we're talking like Aristotle days, 300 ish B.C., which rests, of course,
12:55 Daniel Whiteson? on the knowledge that the Earth is a sphere and not a flat disk.
13:00 Kelly Weinersmith? I've been reading a little bit more about the history of like medicine and the just kind of like the history of science. Does every piece of information we know like go back to Aristotle? It feels like everybody has to have a like, what did Aristotle think about this moment in their history?
13:16 Daniel Whiteson? Yeah. Well, you know, Aristotle and the Greeks get a lot more credit than people usually give them because their theory of geocentrism was honestly pretty good.
13:25 Kelly Weinersmith? Okay.
13:25 Daniel Whiteson? Like it fit the data. It was the best explanation for the data and we're going to explain why in a minute. And I've often been guilty of like dismissing the Greeks as being pre-scientific about just like sitting in a cave and thinking about the universe. But that's too simple. Like they really did use data and look at the universe and try to make their theories fit with their observations. And it's like, not technically empiricism because that didn't come for a couple thousand more years, but it's almost empiricism. I mean, like, how did they know that the earth was a sphere to begin with? You know, they could see that like the constellations were different in the northern and southern hemisphere, right? You see different stars, which suggests you have a different view because you're
14:06 Daniel Whiteson? looking out on a different part of a round ball, right? You're not just standing on the disc where you would see the same view all through the year. They could also see the shape of the earth when they saw lunar eclipse, right? Remember, a lunar eclipse is when the earth is between the sun and the moon. So the earth is making a shadow on the moon instead of the moon making a shadow on the earth, which means you can see the shape of the earth on the moon. It's super amazing, right? It's like the universe is revealing the shape of the earth. It's like if you did hand puppets, right? You stood up on the edge of the earth and you stuck your hand out during a lunar eclipse, technically you could do like hand puppets on the surface of the moon. The moon is the screen there, right? It's amazing.
14:51 Kelly Weinersmith? But wouldn't a flat Maybe I'm not gonna, maybe I'm not gonna want this on the record.
14:56 Daniel Whiteson? No, no, do it, do it.
14:57 Kelly Weinersmith? Wouldn't a flat disk make a similar shadow as a sphere?
15:01 Daniel Whiteson? A flat disk would make a similar shadow if it was perfectly aligned, right? Otherwise, it would be like an ellipse, or it would look like a line, depending on its alignment between the earth and the sun. So you could, if you only had that one piece of data, argue that the earth could be a flat disk that was perfectly aligned to make a circular shadow. Yes.
15:20 Kelly Weinersmith? Okay.
15:21 Daniel Whiteson? So that one piece of information is not enough.
15:23 Kelly Weinersmith? Got it. Okay. And then I had heard that another piece of information that they'd use is they'd watch ships. And as the ships went away, you could see the like bottom part of the ship going away and you'd, but you'd still see their, uh, the masts and the sails.
15:35 Daniel Whiteson? Yeah, exactly. You can literally see the curvature of the earth. If you look over long distances, because you can see the top of the ship and you can no longer see the bottom of the ship. Right? And there's also an experiment they did where you look at shadows at different parts of the earth. And you know, if the sun is straight overhead in one city, so it makes no shadow, you can measure the length of a shadow in another city. And you can deduce whether or not you're on a flat surface or on a curve based on the length of that shadow. And flat earthers also argue like, oh, but that would also be true if the sun was not super far away. If it was close, it could cause the same effect. But you can rule that out by just adding a couple more sticks and measuring more shadows. So anyway, the earth is not flat and the Greeks knew that, right?
16:20 Daniel Whiteson? And that raised an obvious question to them, which is like, okay, if the earth is a sphere, why don't we fall off the bottom of it? Right? And why does the stuff in the sky not fall to the earth? Cause like you drop an apple, it does fall. You don't need Newton to observe apples falling, see that apples do fall. So this is a very natural next question for Aristotle. And this is where his theory sort of falls apart because his theory here is sort of just like, well, because. He says apples and people are made out of a certain kind of stuff, which we'll call like earthy stuff. And earthy stuff is defined as stuff that falls to the center of the universe. For no reason, that's just the nature of earthy stuff to do.
17:03 Daniel Whiteson? And heavenly stuff, star stuff, doesn't. It's embedded in crystal spheres and so doesn't fall. And so like, why don't we fall off the surface of the earth? Because it's not in our nature to fall off the surface of the earth. We are made out of earthy stuff and everything falls towards the center of the universe, which is the center of the earth. And everything out in the heavens is not made of that stuff. And so it doesn't fall to the earth. And it seems kind of quaint now, doesn't it?
17:27 Kelly Weinersmith? Yes. Yeah. Why don't I go to California? Well, because I'm made out of Virginia stuff. And so I, I tend to fall into Virginia. And, uh, yes. And you're made of like crystals that stay in California.
17:39 Daniel Whiteson? Yes, we are made of crystals out here. Exactly. Hence our shimmering lifestyle. And because stuff doesn't fall to the earth, it's made out of heavenly stuff and therefore it's perfect and it moves in perfect circles. And this is the first idea that the earth is at the center and everything moves around it. And you might initially think like, well, this is kind of a goofy idea, right? Why did it come up with this plan? And this is the first place where I think the Greeks don't get enough credit. And the story is more nuanced than people understand because the Greeks considered the idea that the earth was not at the center. They thought about, well, what if the sun is at the center, you know, could that be? And they examined what that would mean for the solar system. And they actually thought
18:23 Daniel Whiteson? of a way to test it, which is super cool, right? Because you shouldn't just sit in your toga and eat olives and think about the universe. You should figure out a way to force the universe to reveal to you the truth, right? That's what experimental physics is all about. And they realized that if the earth was not at the center of the universe, if it moved around the sun, right? If the sun was at the center and the earth moved, they should be able to tell because they should see the stars wiggling.
18:50 Kelly Weinersmith? Oh, and is there a technical name for wiggling?
18:55 Daniel Whiteson? Are you insisting that I use a Latin term instead of explaining the concepts?
19:00 Kelly Weinersmith? No, no, let's just, let's stick with wiggling. That's it. The whole episode, I want you to stick with wiggling.
19:05 Daniel Whiteson? Well, you want to learn more about it, you're gonna need to know the official term, which is parallax, but we can call it stars wiggling.
19:11 Kelly Weinersmith? Oh, oh, oh, oh, wait. So what? So when I want to explain a species, is it okay if I just say, well, the listeners might want to know more about Uplurkis Californiansis, which is why I need to tell you the species name? I didn't realize that worked.
19:23 Daniel Whiteson? If anybody actually wanted to know more and...
19:27 Kelly Weinersmith? Who would not want to know more about brain infecting parasites? Oh, fish.
19:32 Daniel Whiteson? Hard to imagine. Hard to imagine.
19:34 Kelly Weinersmith? All right. All right. Parallax. Got it. Stars wiggling is called parallax.
19:38 Daniel Whiteson? Yeah, exactly. And this is something that's very easy to understand. This is actually how your eyes work to see distance. Like, if you hold your thumb out in front of you and you look at it with one eye versus the other eye, it moves, right? It's not in the same location relative to the two eyes. So your two eyes have a different view of your thumb. And as your thumb gets further away, the difference shrinks. And as your thumb gets closer to your eyes, the difference gets larger. And this is binocular vision. This is how your brain can tell how far away something is. When a basketball is flying towards your head, your brain does this calculation based on the different view from the two eyeballs to tell you how close is it, right? How rapidly is it approaching? And so you can do the same thing with the Earth. If the Earth was moving around the
20:22 Daniel Whiteson? Sun, then we should get two views of the heavens at different times of year. Like in June and in December, we would have a different relationship to the stars and we should see them move, right? We should see them wiggle. And they looked. They looked at the stars, unlike my kids, and they did not see them wiggle. And they said, oh, look, the stars are not wiggling. Therefore, because the stars must be close enough to wiggle if we were moving, we are not moving. And that was the flaw in their logic. They could not fathom that the stars were far enough away to be wiggling but invisibly because they were so crazy far away. And they said, well, the stars can't be that far away and
21:05 Daniel Whiteson? we don't see them wiggling, therefore, the Earth is not moving. And that is solid logic.
21:10 Kelly Weinersmith? But the stars are so tiny. How could they not consider? Well, you know what? I should. That is impressive that they did the experiments and they figured out parallax that like props to the Greeks.
21:21 Daniel Whiteson? Exactly.
21:22 Kelly Weinersmith? In their togas.
21:23 Daniel Whiteson? And of course, now we know with hindsight that the stars were wiggling. It's just that the wiggle is so small because the stars are crazy bonkers far away. So much further away than they could even ever imagine. So far away that we didn't see parallax. We couldn't measure it until 1838. Fairly recently. This was just a theoretical concept for a very, very long time. And turns out to be quite relevant to this story. So the Greeks thought of parallax and they ruled out a sun centered universe because they didn't see it. There's a logical flaw there, but you gotta give them props for using experimental data for actually testing these two theories.
22:04 Daniel Whiteson? And if I was in their shoes, I would probably come to the same conclusion.
22:09 Kelly Weinersmith? Yeah, yeah. This is the kind of stuff that keeps me up at night thinking, oh my gosh, what else do we think like, oh yeah, well, we thought of that and we've ruled it out.
22:16 Daniel Whiteson? Exactly.
22:17 Kelly Weinersmith? What else?
22:18 Daniel Whiteson? You make one very reasonable sounding assumption. The stars are not crazy bonkers distant away. And you go down the wrong track for a thousand years.
22:27 Kelly Weinersmith? Or more than a thousand years, but yes. All right, let's take a break. And when we get back, we will jump into the ideas of Ptolemy with a silent P.
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25:56 Daniel Whiteson? Kelly, you are inviting some Greek speaker to write in and tell us that we are mispronouncing Ptolemy. Maybe there's just like a really subtle P in there.
26:05 Kelly Weinersmith? Oh.
26:06 Daniel Whiteson? Ptolemy. I don't know how to do it. Greek speakers write in and tell us if we are mangling Ptolemy and pterodactyls.
26:13 Kelly Weinersmith? Oh, I mean, nobody's going to be surprised. Kelly's mangling names, but all right, let us know.
26:18 Daniel Whiteson? So the first problem with Aristotle's theory that things in the heaven are perfect and move in perfect circles is that they don't.
26:25 Kelly Weinersmith? Uh oh.
26:26 Daniel Whiteson? Right? If you follow the planets, you can see that they do not move in perfect circles in the heavens. They go sometimes into retrograde. This is not an astrology podcast. We're not talking about, you know, whether you should be making big moves in your romance life when Mercury is in retrograde. Retrograde is also an astronomical thing. It's when planets change their apparent direction in the sky.
26:50 Kelly Weinersmith? Are they actually changing direction? Or do they just look like they're changing direction because of how we're moving?
26:55 Daniel Whiteson? What's the difference? I mean, everything is relative, right? And so we are looking at the motion of the planet against the background stars from our point of view. So from the point of view of the sun, planets don't change direction. They move in an orbit, going the same direction all the time. But planets move at different speeds around the sun. And so sometimes they can pass each other. So from our point of view, sometimes it looks like they're moving one way and then we pass them so they're going backwards. And then it looks like they're moving forward again, just like, you know, if you're on Highway and somebody is really far ahead of you. You can tell that they're going forwards because they're passing stuff, right? But then as you pass them, it looks momentarily like they're going backwards relative to you. Right in your car's window, they're going backwards.
27:40 Daniel Whiteson? Then once you're far away from them again, you can tell, oh, look, they're going forwards relative to the background mountains.
27:45 Kelly Weinersmith? Got it.
27:46 Daniel Whiteson? That's sort of what's happening with the planets. If you look at Mars and you write down its location in the sky every night, you'll see it moving through the ecliptic. And then you'll see it go backwards and then go forwards again. It does this like S shaped zigzag. And that was a big problem for Aristotle's theory that like everything is perfect in the heavens and moves in these perfect crystalline circles.
28:07 Kelly Weinersmith? What is the ecliptic?
28:09 Daniel Whiteson? The ecliptic is the plane of the solar system. And so everything in the solar system is roughly in the same plane, right? The sun rotates and rotates around an axis and a plane perpendicular to that axis has all the planets in it. So if you're on the earth and you track the motion of the sun, it moves in a line through the sky. That's the ecliptic and all the planets tend to move in that same line. So if you're looking up in the night sky, you shouldn't just see planets everywhere willy nilly. They're all in the same plane in the solar system, which is a line in our sky.
28:40 Kelly Weinersmith? Got it. Okay.
28:41 Daniel Whiteson? All right. So to explain how do planets sometimes zigzag, they had to add the famously mocked epicycles, right? They're like, okay, we're not giving up on circles. The Greeks love their geometry and their circles, but they're just going to have circles within circles. So now Mars moves in a circle around the earth, but in that circle isn't Mars, it's another circle. So Mars is moving within a little circle and that little circle is moving within a bigger circle.
29:08 Kelly Weinersmith? So is it like every once in a while it'll stop and like take a little walk around a cul-de-sac? Or is it just constantly doing like pirouettes as it goes around in its big circle?
29:20 Daniel Whiteson? It's constantly going around the little circle and the little circle is constantly going around the big circle.
29:25 Kelly Weinersmith? Oh, wow.
29:26 Daniel Whiteson? And the thing about this theory is that it seems kind of ridiculous, but it worked really, really well. Like compared to the previous theory with no circles within circles, it could really describe the data. And you had to take a bunch of measurements and it was a lot of tedious calculations to find all the parameters, like how big is this circle? How fast is it moving? And there's a guy whose job it was to do this in the 1200s. And he's famous for saying, quote, had I been present at the creation of the universe, I would have preferred a simpler design.
29:58 Kelly Weinersmith? Amazing.
29:59 Daniel Whiteson? But for 1,500 years, this is how people understood the motion of the planets in the heavens. And it worked, you know, it described the data really well. So like, yes, circles within circles or epicycles is used to describe the scenario where you like, made your theory too complicated, too baroque. You know, you had to add too many wheels within wheels to fit the data. But it did work, it did fit the data, right? And it's just two layers deep. It's not like circles within circles within circles within circles, right? Just circles within circles, just two layers of circles described what was happening in the heavens for the first time ever. So like, that's a big step forward, folks.
30:38 Kelly Weinersmith? We really don't know of anyone who was like, actually like, wouldn't it all just be easier if we put the sun in the center, guys?
30:45 Daniel Whiteson? That theory was out there, but it was refuted by Parallax.
30:48 Kelly Weinersmith? Oh, okay.
30:49 Daniel Whiteson? We had a reason to reject that theory, right?
30:51 Kelly Weinersmith? Got it, okay.
30:52 Daniel Whiteson? People had thought of it and it was in the bin, right? Like, that theory didn't work.
30:56 Kelly Weinersmith? Got it, got it. So everyone was reminded of Parallax and we still didn't realize the stars were very far away.
31:01 Daniel Whiteson? Yeah, exactly.
31:02 Kelly Weinersmith? Okay, who's next?
31:04 Daniel Whiteson? All right, so next up is a famous player, Copernicus, in the 1500s. And there's a lot of stories out there about Copernicus. He's often described as a Polish priest, but he wasn't actually a priest. He was a canon of the cathedral, which is more like a church administrator. He was never ordained as a priest. But, you know, he was part of the church and he held administrative posts his whole life. And he was not against the church. He developed his theory of heliocentrism, that the sun was at the center. But he didn't want to like, attack the church or embarrass the church. And so famously, he withheld publishing his theory and it was only published on his deathbed.
31:44 Daniel Whiteson? So he got the first printed copy of his theory, May 24th, 1543, the day he died.
31:51 Kelly Weinersmith? Wow, okay, so that's, it sounds less like he didn't want to embarrass the church and more like he was worried about his own skin. If he still wants it to come out, but not until it can't hurt him anymore.
32:03 Daniel Whiteson? Yeah, exactly. There's a lot of complicated stuff in here. Also, it turns out that the printer who printed his book, Andreas Osiander, was trying to like minimize the impact on the church. And so he added a preface which said like, you know, this is just like mathematics. This is not the truth or anything.
32:23 Kelly Weinersmith? Oh, slice.
32:25 Daniel Whiteson? I know. So this might have also helped a little bit, but probably Copernicus would have been furious. Or who knows? Maybe he wanted to like, you know, not embarrass the church and he would have agreed with that. But his motivation was also religious. He just thought that Ptolemy's theory, circles within circles, was kind of ugly. And it didn't reflect like the divine work of the best and greatest artist. So he wanted to put the sun at the center, not because he had any insight into astronomy, and not because it explained the data any better. In fact, it explained the data worse, but because he just felt like the sun should be at the center, because that made the explanation simpler. You no longer needed circles within
33:06 Daniel Whiteson? circles. You could explain retrograde motion. So you put the sun at the center, and now you can just have everything moving in a circle around the sun.
33:14 Kelly Weinersmith? But what about parallax?
33:16 Daniel Whiteson? Yeah, so this does not solve the parallax problem, right? And so this is the reason why people were not going for heliocentrism. For 1500 years, his new theory does not solve that problem. He suggested, well, maybe the stars are just too far away for us to notice, right? Good idea, Copernicus. Everybody thought, haha, that's ridiculous. What are you talking about? But the other thing I think it's important to understand is that when he moves the sun to the center of the solar system, it does not give a better description of the data.
33:48 Kelly Weinersmith? Oh.
33:49 Daniel Whiteson? So even though it's like, we know it's true, and it feels like we're getting towards the truth, his theory did not describe observations any better than Ptolemy's theory of circles within circles, right?
34:01 Kelly Weinersmith? Hmm.
34:02 Daniel Whiteson? It's simpler, but Ptolemy had this flexibility in his theory. It's a little baroque and complicated, but it could describe the data. So what does heliocentrism from Copernicus really get you? It can't explain parallax unless you believe the stars are super duper far away, for which there was no evidence. And it doesn't describe the data any better. So I think people typically like, this was the revolution in astronomy, but it really wasn't.
34:25 Kelly Weinersmith? Okay, it's just pretty.
34:26 Daniel Whiteson? It's just a little prettier. Yeah, exactly.
34:30 Kelly Weinersmith? Was that the dominant theory? Or was this just a theory that was out there? Because it, from what you've said to me, it's not clear that this should have become immediately the dominant theory.
34:40 Daniel Whiteson? Yeah, what we really needed at this point was better data.
34:43 Kelly Weinersmith? Okay.
34:43 Daniel Whiteson? You know, the reason we couldn't tell the difference between the two theories that both of them described the data is the data was kind of fuzzy. This is pre Galileo, right? So we don't have telescopes looking at the sky, taking careful measurements. This is all naked eye astronomy. And so that really relies on like people's ability to take measurements. And so it wasn't until Tycho Brahe, who built a world-class observatory, using money from King Frederick of Denmark and took really careful observations, he got higher quality data that finally let us move forward and understand something else about the universe.
35:20 Kelly Weinersmith? So I think we probably can't have a conversation about good old Tycho without talking about his nose. So tell us the nose story.
35:30 Daniel Whiteson? So Tycho Brahe, kind of a crazy dude and kind of unhinged and also a little bit mean. And when he was 20, he fought a duel with a fellow Danish nobleman over math, right? They had an argument about like, who was the better mathematician? And they fought a duel like with swords and he lost a big chunk of his nose. And so for the rest of his life, he had a prosthetic nose, which was like brass or maybe a silver gold alloy that he had to stick on because otherwise he just looked really weird and you can't be like part of polite society with a huge slice of your nose taken out. So he walked around with this like box of adhesive paste to stick this fake nose onto his face.
36:14 Kelly Weinersmith? Which I think is a failing of polite society back then and remains to be a failing of polite society today. We should all be much more chill, but anyway.
36:22 Daniel Whiteson? But in 1576, King Frederick of Denmark gave him an island. This is the island of then, which I've been to. It's a beautiful place. You can bike around, it's gorgeous. He has a castle there, Ranembor, Castle of the Heavens, later renamed Castle of the Stars, Stianenborg.
36:42 Daniel Whiteson? And it's essentially one of the first astronomical research facilities in the world, you know, like built to see the stars, to take careful measurements.
36:51 Kelly Weinersmith? So if you have a facility that's gigantic, you probably need a lot of people to work at that facility. What was it like working for good old Brahe?
37:00 Daniel Whiteson? Yeah. So Brahe was not a kind employer. You know, he was famous for being brutal to the local peasants, you know, demanding all sorts of stuff from them. He was also a really weird guy. He had like an elk that he kept in his house and sometimes he would feed it too much beer and it would fall down the stairs.
37:18 Kelly Weinersmith? What?
37:18 Daniel Whiteson? Like, this was a weird dude.
37:20 Kelly Weinersmith? Okay.
37:20 Daniel Whiteson? He apparently died of a bladder infection from sitting at a royal banquet for too long and refusing to get up to urinate, which was apparently rude and rupturing his bladder because of that. So he was definitely a weird guy, but there's some things about him which resonate with me. Like, he was trying to look at the heavens and to observe things. And there was supposed to be an alignment of Jupiter and Saturn. But it happened two days after it was predicted. And that's because the measurements were just not great. Like, we did not have precise measurements of stuff. And so predicting what was going to happen in the sky is limited by the measurements that we could make. So that was his motivation. It's like, I want to understand the heavens better. So he measured the positions of celestial
38:03 Daniel Whiteson? objects in the sky to one arc minute, a sixtieth of a degree, which is precision of like a fingernail at arm's length, right? These are naked eye observations. No telescopes, no lenses, right?
38:18 Kelly Weinersmith? That's amazing.
38:18 Daniel Whiteson? So this data that he gathered is like 10 times more accurate than any data anybody's had about the sky. And this is what fueled the revolution in astronomy is like needing to actually describe the universe more precisely. And neither the Ptolemaic nor the Copernican models fit that data.
38:38 Kelly Weinersmith? Oh, boy.
38:38 Daniel Whiteson? So you might be expecting, oh, we take better data. And that's when we learn the heliocentrism is the truth. Oh, no, we take better data. We discover neither of those two models actually worked.
38:49 Kelly Weinersmith? So what do we do?
38:51 Daniel Whiteson? Yeah. Tycho could not make this work either, right? And the issue, of course, was not going to be solved until later when Kepler came up with his ideas of ellipses, but we're not there yet because Tycho rejected Ptolemy's theory that the Earth was at the center of the universe. He also rejected Copernicus's theory that the sun was at the center of the universe. He had his own theory, the Tychonic system of the solar system, which sounds like a diet plan from medieval Europe, but it was like a new vision of how the universe might work.
39:24 Kelly Weinersmith? I hope it doesn't involve drinking beer and sitting at a table for a real long time.
39:28 Daniel Whiteson? With an elk.
39:29 Kelly Weinersmith? Sounds dangerous.
39:32 Daniel Whiteson? So he liked the idea that the Earth was in the center. Tycho said the Earth was a hulking lazy body unfit for motion. And it made no sense to him that the Earth was in motion. And also remember, we were not seeing parallax, so he really wanted to keep the Earth at the center of the solar system. But he also liked the simplicity of the Copernicus system, right? Where you don't have circles within circles, where you can explain retrograde motion by having the planets move around the sun. So Tycho was like, hmm, I want the Earth at the center and I want the planets to move around the sun. Porque no los dos, right? I don't think he spoke Spanish, but that was the inspiration, right?
40:10 Kelly Weinersmith? And it was probably before that commercial, so.
40:15 Daniel Whiteson? So that's the Tychonic model of the solar system is you have the Earth at the center. The sun moves around the Earth and all the planets move around the sun, not around the Earth, right?
40:27 Kelly Weinersmith? That's complicated.
40:28 Daniel Whiteson? So it's geoheliocentric, right?
40:31 Kelly Weinersmith? Wow.
40:32 Daniel Whiteson? So the Earth is at the center, the sun moves around the Earth and all the planets orbit the sun. So like together, our sun is bringing all the planets with it as it orbits around the Earth. It's kind of bonkers.
40:45 Kelly Weinersmith? Does this actually do a great job with the data?
40:47 Daniel Whiteson? So you know, this explains retrograde motion, right? Because you have the planets moving around the sun, not the Earth.
40:53 Kelly Weinersmith? Okay.
40:54 Daniel Whiteson? And it explains no parallax observation. We didn't see parallax. Why? Because the Earth was not moving relative to the distant stars, right?
41:03 Kelly Weinersmith? Okay.
41:03 Daniel Whiteson? So this was kind of a great idea. And this Tychonic model, though you never hear about it anymore, survived for centuries and was taken seriously for centuries because it fit the data very well.
41:15 Kelly Weinersmith? Wow.
41:16 Daniel Whiteson? Now, he still used circles, right? This is pre Kepler. So he wasn't actually able to fit his own data any better than Ptolemy or Copernicus, right? Anybody still using circles for these planets was still not getting great predictions because actually the planets move in ellipses, not in circles. But he did explain retrograde motion and parallax observation. And Tycho thought that Copernicus's idea that like the stars were so distant and that's why we couldn't observe parallax was crazy because he calculated they would have to be at least 700 times more distant than Saturn, which to him was like a bonkers number. If you can see their size and you've an estimate of their distance, you can calculate how big they must be.
41:59 Daniel Whiteson? And he got a number which was huge, much bigger than the sun. And he was like, well, that's crazy. Now, of course, we know there are some really, really big stars out there and they were really on to something, but these numbers were just so bonkers to them that they dismissed it, right? So Tycho Brahe preferred putting the Earth at the center of the solar system rather than accepting the stars were super distant and some of them were super duper big.
42:25 Kelly Weinersmith? I thought maybe you said this idea was accepted for centuries and maybe I misheard you, but I thought it looks like Kepler in like decades comes up with a better idea. But were Kepler's ideas not?
42:36 Daniel Whiteson? So Kepler, soon after Tycho Brahe, comes up with the idea of ellipses, right? Because he's Brahe's assistant and he's tasked with this job of like, look, I like this theory, but it's not really quite working. It can't explain the data. And he was struggling and struggling and struggling to make the orbit of Mars work in particular. So Kepler couldn't make this work. He struggled for years and finally he was like, okay, let's use ellipses.
43:01 Kelly Weinersmith? Let's take a break and when we come back, let's go ahead and settle this debate, which is what you'd expect us to do in the third segment of our show.
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46:29 Kelly Weinersmith? And we're back. And we are finally gonna settle this geocentrism, heliocentrism debate. What's going on with Parallax? Daniel, let's settle this thing.
46:39 Daniel Whiteson? Right, so we have the Ptolemaic version. The Earth is at the center. We have the Copernicus version. The sun is at the center. We have the Tychonic version, which puts the Earth at the center and all the other planets orbiting the sun, right? And none of them are working very well. The reason is that all of them are still based on circles. All the orbits are circles. So Kepler comes in. He's trying hard to make this work. Can't make it work. He comes up with the idea of ellipses, right? He adds this to Copernicus's theory, right? So the Kepler view of the universe now is Copernicus, but with ellipses instead of with circles. And this matches the data. This works really, really well.
47:18 Kelly Weinersmith? And ellipses being long circles?
47:22 Daniel Whiteson? So ellipses are like the shape of an egg, right? So a circle is perfectly round and ellipse is like a squished circle, right?
47:28 Kelly Weinersmith? Got it.
47:28 Daniel Whiteson? And he can also upgrade Tico Brahe's theory to use ellipses, right? So now the Tychonic model can have ellipses, the Copernican model can have ellipses. The Ptolemaic model does not allow for ellipses because you know, they're going for like perfect circles, right? But you can always just add more ellipses to Ptolemy. So it is possible to fit Ptolemy's theory to Brahe's observations. You've just got to add more and more circles. And so it's not really true that Tico Brahe's data killed the Ptolemaic system, right? Because the Ptolemaic system allowed you to just add more and more circles as you liked. What really killed the Ptolemaic system was Venus.
48:10 Kelly Weinersmith? What? How did the goddess of love kill Ptolemy?
48:15 Daniel Whiteson? So remember, Ptolemy could always just add more circles. No matter what data you took, he could actually fit it. But Galileo realized that observing Venus would help us understand whether Venus was orbiting the sun or orbiting the earth. So Galileo comes around late 1500s, early 1600s. And he realized that your view of Venus would depend on whether it was orbiting the earth or orbiting the sun.
48:40 Kelly Weinersmith? Okay.
48:40 Daniel Whiteson? So if Venus is orbiting the sun, right? It's moving around the sun. There's going to be some point at which Venus is on the other side of the sun than we are, right? And the sun is going to be between earth and Venus. And in that configuration, we should see an entire side of Venus lit up, right? We should see like a full side of Venus. Venus should be like full in the sky, not a crescent, but a full circle in the sky.
49:07 Kelly Weinersmith? When it's on the other side of the sun?
49:09 Daniel Whiteson? When it's on the other side of the sun, because in the light from the sun hits the whole surface of Venus and then we see that whole thing. Just like how you can see a full moon, right? You can see a full moon when the whole side of the moon is being illuminated by the sun.
49:23 Kelly Weinersmith? Okay, I guess when I'm imagining it's on the other side of the sun, I can't see it because it's blocked by the sun. So what, what is my mental model missing there?
49:31 Daniel Whiteson? You're right that if it's exactly behind the sun, you couldn't see it. But now let it move like a little bit around from behind the sun. And you can see essentially the entire surface of Venus is lit up by the sun, right?
49:42 Kelly Weinersmith? Perfect. Okay.
49:43 Daniel Whiteson? Okay. So now in Ptolemy's model, Venus is orbiting the earth and not orbiting the sun. And so never is it on the other side of the sun. In Ptolemy's model, Venus has its orbit around the earth and the sun has its orbit around the earth and their relative distances are fixed. And so in Ptolemy's model, Venus is always between the earth and the sun. And so you should never see like the full phase of Venus. You always see a crescent.
50:12 Kelly Weinersmith? Okay.
50:13 Daniel Whiteson? So you can just look, you just watch Venus. And if you look at Venus, you can see that the phases of Venus are perfectly predicted by Venus orbiting the sun instead of orbiting the earth. So it's the phases of Venus that finally kill off the Ptolemaic system.
50:29 Kelly Weinersmith? Direct hit. Ptolemy goes down.
50:31 Daniel Whiteson? But here's an important wrinkle that I didn't fully understand until recently. It does not kill off Tycho Brahe's system, right? So we have Copernicus, who says the sun is at the center and everything is orbiting the sun. We have Tycho Brahe, who says the earth is at the center, the sun is orbiting the earth and all the planets are orbiting the sun. That's consistent with the phases of Venus, right? So Tycho Brahe's system is not killed off by the phases of Venus. It's still around.
51:01 Kelly Weinersmith? How do we kill that one off then?
51:03 Daniel Whiteson? The thing to understand about the difference between the Copernicus system and the Tycho Brahe system is that even though they sound really, really different, they're actually totally equivalent for local motion. It's just a coordinate transformation. It just says, are you viewing it from the sun or are you viewing it from the earth? They make exactly the same predictions for where things are in the solar system relative to each other. Their only difference is who's moving relative to the distant stars. Like is the earth motionless with respect to those stars? Or is the sun motionless with respect to those stars? Within the solar system, they're exactly the same prediction.
51:43 Kelly Weinersmith? Okay. And just to remind people like me again, whose brains don't hold information, Copernicus predicted-
51:49 Daniel Whiteson? The sun at the center.
51:50 Kelly Weinersmith? The sun at the center and Tycho has the-
51:53 Daniel Whiteson? Yeah.
51:53 Kelly Weinersmith? Earth at the center, the sun goes around the earth and the planets go around the sun.
51:58 Daniel Whiteson? Yeah. And you said, "That sounds a lot more complicated."
52:00 Kelly Weinersmith? Yeah.
52:01 Daniel Whiteson? And it seems more complicated and it's harder to hold in your mind, but any prediction it makes is exactly the same as the Copernican system for inside the solar system. It's just a coordinate transformation. It just says, "From whose perspective are you seeing this?"
52:15 Kelly Weinersmith? Okay.
52:15 Daniel Whiteson? So the only way to tell the difference between these two systems is to ask, "Well, who's moving relative to the distant stars?" And you might think, "Okay, finally, here's where parallax has got to come in. Eventually, we figured out parallax and that's what killed Tycho Brahe's system, right?"
52:33 Kelly Weinersmith? Maybe.
52:34 Daniel Whiteson? Wrong.
52:34 Kelly Weinersmith? Oh.
52:35 Daniel Whiteson? It was not parallax that killed off Tycho Brahe's system. It was something totally different. It was stellar aberration.
52:43 Kelly Weinersmith? I don't know what that is at all.
52:45 Daniel Whiteson? Stellar aberration is super famous in the history of physics for killing off the ether theory. That's a whole other podcast episode.
52:51 Kelly Weinersmith? Mmm, fun.
52:52 Daniel Whiteson? But the idea is you can measure our velocity relative to the stars by looking at how their angle changes during the year. This is different from parallax, right? Parallax just says that if you're in a different location, you'll see them at a different point in the sky. This is sensitive to our velocity relative to the stars. Because if you imagine like the light coming from the star, it's going to come down your telescope tube. So you have to point your tube of your telescope where the star is. But if the star is moving, right, then the light's going to come in at a different angle. And so you have to point your telescope tube slightly differently in order to catch it.
53:30 Kelly Weinersmith? Okay.
53:30 Daniel Whiteson? And so the star appears at a different place in the sky than it really is if it's in motion. Now, if you have constant velocity relative to the stars, then you'd see them at a shifted angle all year. You wouldn't be able to tell anything. But if our velocity changes during the year because of our orbit around the sun, then this aberration, this change in the angle, changes with respect- Respect to the year. One easy way to think about it is that parallax comes from changing your position, while aberration comes from changing your velocity. Parallax is the same effect you see when you look at your thumb with one eye and then the other. Aberration is more like tilting an umbrella forward when you're walking through the rain,
54:12 Daniel Whiteson? because your motion changes the apparent direction the raindrops are coming from. And this was observed 110 years before parallax. And that proves that the Earth is moving relative to the distant stars, just the way you'd expect if it's orbiting the Sun. If you did that measurement on the Sun, you'd see much less aberration, because the Sun is moving less relative to the distant stars.
54:36 Kelly Weinersmith? Okay.
54:36 Daniel Whiteson? And so this is what finally killed off Tycho Brahe's theory that the Earth was at the center and not moving relative to the distant stars.
54:45 Kelly Weinersmith? Ha ha. Okay. And so now Kepler wins.
54:49 Daniel Whiteson? So now Kepler and Copernicus win. And it's not until 100 years later that we observe parallax. The thing that the Greeks said was the key to understanding whether the Earth or the Sun is at the center of the solar system. And this comes because Bessel invented something called a heliometer, which uses relative measurements rather than absolute measurements. So instead of like trying to really precisely measure the location of the stars, he just measured the motion of the stars. So it's sort of like subtracting away a source of your systematic uncertainty to only look at changes in your measurements. So really cool story there, but 100 years too late to actually be relevant to this debate.
55:33 Kelly Weinersmith? What do you think the takeaways are here? Because like, so you've got a bunch of models that do a good job of explaining the data, but they were still wrong. But we kept thinking about it and trying to do a better and better job. But how would, what is the Daniel uplifting message here?
55:49 Daniel Whiteson? You know, I think that the story is a lot more complicated than people usually tell it. You know, I think the not widely understood takeaways are that Copernicus and Ptolemy both described the pre Kepler data really, really well. And the Greeks had a good reason to put the Earth at the center of the solar system. And that there was a third player in this whole debate, right? Tycho Brahe is sort of forgotten. Nobody talks about the Tychonic system, even though it survived until the 1700s. And that Kepler's analysis and ellipses didn't actually disprove geocentrism, right? It just made Ptolemaic less likely because it required more circles within those circles. It was the phases of Venus that finally killed off Ptolemy. And that it wasn't until aberration and then
56:32 Daniel Whiteson? eventually parallax, that Tycho Brahe's system was finally disproven.
56:37 Kelly Weinersmith? The more data you have, the better you're gonna do. We had to know about Venus, we had to know about parallax, we had to know about stellar aberrations. All of this came together to tell our story.
56:47 Daniel Whiteson? Exactly. And so this tells you that our exploration of the universe can go down weird paths for hundreds of years, sometimes, before somebody takes the right piece of data, or has the right idea. And that many of the stories we tell about the history of scientific discoveries are vastly oversimplified. And that if you're standing at the forefront of human knowledge at any given moment, it's not always obvious what the next step is, even if it seems like it in hindsight.
57:13 Kelly Weinersmith? That's right. All right. Thanks, Daniel, for this walk through science history. I had a great time. Until next time, extraordinaries.
57:26 Daniel Whiteson? Thanks, everybody for listening. Please go and do us a favor and rate the show on whatever podcast app you're using. It really helps people find us.
57:34 Kelly Weinersmith? Daniel and Kelly's Extraordinary Universe is edited by the amazing Matt Kesselman.
57:39 Daniel Whiteson? He really is a wizard. You can also find us online on Blue Sky, Instagram, and X, D and K Universe. Come engage with us.
57:49 Kelly Weinersmith? You can email us at [email protected] . We really do want to hear from you.
57:54 Daniel Whiteson? And you can find our website, www.danielandkelly.org, where you'll also find an invitation to join our Discord, where everybody comes and talks about the amazing universe.
58:06 Kelly Weinersmith? And we also have the most amazing moderators. This is an iHeart Podcast. Thanks for joining us.
58:15 Speaker 04 Snoring, gasping for air during sleep, daytime sleepiness? I'm Shaquille O'Neal and this shouldn't be anybody's experience. Ask your doctor about Zepbound Trzepatide, the first and only FDA-approved prescription medicine for moderate to severe obstructive sleep apnea in adults with obesity.
58:31 Speaker 05 Zepbound is a prescription medicine used with a reduced calorie diet and increased physical activity to help adults with moderate to severe obstructive sleep apnea (OSA) and obesity to improve their OSA. Zepbound is approved as a 2.5, 5, 7.5, 10, 12.5, or 15-milligram injection. Zepbound contains Trzepatide and should not be used with other Trzepatide-containing products or any GLP-1 receptor agonist medicines. It is not known if Zepbound is safe and effective for use in children. Don't share needles or pens, or reuse needles. Don't take if allergic to it, or if you or someone in your family had medullary thyroid cancer, or if you've had multiple endocrine neoplasia syndrome type 2. Tell your doctor if you get a lump or swelling in your neck. Stop Zepbound and call your doctor if you have severe stomach pain or a serious allergic
59:16 Speaker 05 reaction. Severe side effects may include inflamed pancreas or gallbladder problems. Tell your doctor if you experience vision changes before scheduled procedures with anesthesia. If you're nursing, pregnant, plant-to-be, or taking birth control pills. Taking Zepbound with a sulfonylurea or insulin may cause low blood sugar. Side effects include nausea, diarrhea, and vomiting, which can cause dehydration and worsen kidney problems.
59:38 Speaker 04 Talk to your doctor. Call 1-800-545-5979 or visit zepbound.lily.com.
59:46 Kelly Weinersmith? Hello everyone and welcome to Rushing the Field. I'm Nicole Auerbach.
59:50 Speaker 04 And I'm Joshua Perry.
59:52 Kelly Weinersmith? We're so excited to be here to chat about our favorite thing in the entire world, college football.
59:57 Speaker 04 From the biggest headlines and breaking news to the stories shaping the sport behind the scenes, Rushing the Field is your home for everything college football.
1:00:04 Kelly Weinersmith? Whether you're obsessed with rankings, rivalries, or game day drama, we've got you covered. Watch Rushing the Field on NBC Sports now.
1:00:15 Kelly Weinersmith? Most dog food brands don't really want you seeing how their food is made. Just Food for Dogs is the opposite. They actually invite you in. You can walk into any of their kitchens and see real, human-grade ingredients, like chicken, beef, carrots, and peas, being prepared right in front of you. It's real food, made in real kitchens. Nothing is hidden behind labels, and that kind of transparency says a lot. Nothing to hide, everything to love. Go to justfoodfordogs.com and get 50% off your first order. This is an iHeart Podcast. Guaranteed human.
Previous Listener Questions #40 Next What is a species? (featuring Dr. Scott Egan) Page updated October 30, 2026 · transcript and summary are machine-generated