right so it took until the Renaissance to figure out how to fix everything does anybody new who came along and brought back the idea that the Sun was at the center of everything who's famous for giving us the modern heliocentric model say money No starts with a C I'll give you that hint you may have learned about this guy in school and then as you guys are doing I'm gonna bring up a picture of him Oh somebody commented that the the ancient Greeks dropped the ball that that's a good one I'm gonna steal that one and use that one in future semesters yes so who came along in the Renaissance to to start bringing the Sun back into the picture that was Copernicus okay and here's a picture of him right here just really Rocking you know this this hairdo right here Copernicus and in case you can't read that that's Co p ER in ICU s but actually if you know anything about history spelling was not set in stone back then so he actually spelled his name a bunch of different ways throughout his life but Copernicus is what we usually go with at this point yeah so this was the Renaissance um in order to be a scientist at this point in history you pretty much had to be a rich person okay you pretty much had to be a rich person because you know science didn't pay very well usually unless you could get like a wealthy donor to support you so most of the scientists we're talking today that's not the case anybody no matter how poor can eventually become a scientist well okay probably not anybody but most people can do it right so this was a very rich guy right here and he spent a lot of his time reading about astronomy and researching these problems and he didn't like that the most accurate star charts were leading to this giant ugly messed up system of geocentric circles on circles on circles and he realized here we go that you could explain retrograde motion you could explain why the planets go backwards sometimes in a much simpler way by just putting the Sun in the center okay uh yeah you know Columbus was also a rich guy but this guy not a like Christopher Columbus okay so this guy this guy had a better head on his shoulder than Columbus did so check this out here we go so let's put the Sun in the center just like Copernicus thought and see how that fixes the problem so let's pop the Sun there great got a restart restart please stop talking but not you guys I'm talking to my computer go away one second technical difficulties control-alt-delete there we go good old control-alt-delete works every time there we go okay so we're back sorry about that so check this out so Copernicus put the Sun in the center of everything so let's put a big s on that and if he's putting the Sun in the center that means where is the Earth if the Sun is in the center where's the Earth gonna be here we go Oh looks like I had a little bit of delay I'll just go ahead and move on the earth has to be orbiting around the Sun right it's got to be orbiting around the Sun if it's not in the center then the Earth's gotta be orbiting around so here's the earth and the rest of the planets were orbiting around the Sun also some of them were closer to the Sun than us specifically Mercury and Venus and then Mars and a few of the other planets were farther out okay so every planet had its own orbit around the Sun the only thing that he had orbiting around the earth was the moon okay which is correct now couple of important things here these orbits in spite of my terrible drawing Copernicus thought these orbits were perfect circles based on observations of the planets okay he thought that these orbits were shaped like perfect circles and that the Sun was 100% exactly at the exact center of these orbits okay now check this out this means and this is the important part this is the important part he figured out that these planets and the earth were all moving at different speeds okay they don't have to move at the same speed Oh somebody's asking if the planets were named by them they were named um so there was Mercury and Venus and Mars and Jupiter and Saturn they didn't know about Uranus and Neptune yet Uranus wasn't discovered until telescopes those two you can't see with the naked eye so it took a much longer to figure it out that they existed but they did have the right names it's just that even in Copernicus's time we people still thought that they were weird stars they had the names Mercury and Venus but they thought that they were strange stars so even Copernicus didn't know that these other planets were places like Earth he thought they were just weird stars that orbited the Sun okay so he's still not 100% right but this is a lot more right than than the people before him right now check this out how does this explain why planets look like they go backwards sometimes so here's my first question on that do planets actually go backwards like do they actually go backwards around the Sun no no they don't so what Copernicus figured out is that retrograde motion is an optical illusion that comes from the fact that earth is moving okay let me explain it when it comes to Mars it's the easiest one for me to explain okay here's what Copernicus thought let me let's not think about the plants for a second let's use a metaphor let's think about this I assume that you have driven on the highway or at least been in a car that was driving on the highway at some point and the reason I'm talking about highways and not regular streets is that highways have multiple lanes and not every Lane goes the same speed right not every lane goes the same speed we have what we call the fast lane and the slow lane right where is the slow lane where's the slow lane on the highway where are you where if you're gonna be moving slow where should you be on the highway on the right and if you're going fast you should be on the left do people actually do that no it's chaos out there and also let the noble were at it let's assume that everybody on our side of the highway is going forward okay let's assume everybody is going forward have you ever been on the highway when somebody came the wrong direction like on the actual highway have you ever seen somebody going the wrong direction on the highway that happened to me one time I was I mean I I didn't drive the wrong way on the highway I was driving along and somebody was coming the other way on the highway that was one of the most terrifying things I have ever seen if you've never seen it you don't want to see it because it's like oh no this is this is not like you see it and you're like oh no someone's gonna die today that's that's what's gonna happen in that situation anyway for this metaphor let's assume that's not happening and everybody's going forward okay so everybody's going forward on the highway okay let's say that you are in the fast lane okay so this is this right here this is you okay this is you actually let me let me make myself big on here this is you okay and this is somebody in the slow lane okay so you're moving forward and let's say the person in the slow lane is ahead of you you're both moving forward but if you're moving faster than them what will you eventually do if this person's moving slow and you're moving fast what will eventually happen if you're in different lanes you're gonna pass them right even though you're both going forward eventually you're going to pass them okay yes and here's the thing if you're coming up behind a slow car you can see that they're going forward but while you are passing a car while you are passing a slower car what does it look like there which way does it look like they're going when you're passing them when you're passing that car which way does it look like they're going like if you come along if I'm gonna pass Copernicus here it looks like they go backwards while you're passing them and then if once you get far enough ahead you can see that they're coming forwards again you know they're not actually going backwards they just look like they're going backwards right so what am I getting at here let's see if we can figure this out here's a hint we on the earth are orbiting around the Sun faster than Mars is we're both going the same direction but earth moves faster than Mars so what does that mean that means every once in a while what will earth do what will earth do every once in a while in this system what happens every once in a while yeah we pass Mars every once in a while we pass Mars every once in a while and based on what we've just been saying what's gonna what's it gonna look like Mars is doing when we're passing it when we pass Mars what's Mars gonna look like it's doing I think you guys are getting it it's gonna look like it moves backwards it's gonna look like it moves in Reverse so retrograde motion is just us passing planets okay as we all go around the Sun in one direction whenever we pass a planet it it has retrograde motion which is just an optical illusion making it look like it went backwards during the pass okay so yeah and he is able to explain that without making the system any more complicated so we can just have this so that's a much more simple explanation than adding a whole bunch of junk to your system to make it so the planets could go backwards