 Greetings, and welcome to the Introduction to Astronomy. In this video, we are going to look at the Flat Earth Society and what their understanding of the nature of the world is. And one of the reasons we want to look at this, why would we study something like this in an astronomy class when really flat earth ideas of the flat earth are not really astronomical? Well, the idea is that we really need to look at other ideas even if we know that they are wrong. So I would believe that the flat earth people are completely wrong, that the earth is not flat, that it is very much spherical, and that we have significant evidence that has demonstrated that over the centuries. But we really want to be able to truly understand the nature of this, and it helps in any discussion to be able to look at the arguments that an opposing group puts forward and to be able to better understand them and to be able to argue against them. So what do I believe? Well, I would say that yes, the earth is round. The earth is not a flat disk in any way. And we need to look at this. This has been proved by many observations, including NASA flights. So what I am looking at here that I just wanted to clarify, I am not in any way endorsing the arguments of the flat earth society. I am simply putting them forward the way they explain things and then showing the methods that are used to explain those in what astronomers will tell you are the correct observations and what we actually see, what NASA has given us, and what observations here on earth explain. So I don't want you to take what I'm saying is saying that I am arguing for a flat earth more that I am trying to get you to think about the different arguments and not just saying this is ridiculous move on, but to actually think of their arguments and to be able to refute those arguments. So let's start out by looking at some of this. And what we want to look at first is what is the model of the flat earth that they use. In many cases people will think of this as a flat piece of paper. And that's when the sometimes we think of it as being completely ridiculous because how would we sail around the world? We could not travel around the world if the earth were flat, the oceans would fall off the edge. And in reality that is not what the flat earth people believe. They actually look at there that the earth is a disc, so a circular disc, the north pole being at the central portion of the disc here, and then the Antarctica stretched around the outer limits in an impenetrable ice wall. Well that would explain why the oceans do not fall off. The water is held in by this great ice wall at the edge. So this means that we can do things like circumnavigate the world. We can travel around the world and never reach an edge. We can go from one point to another around it and come back to our starting point. So it does not argue against that, but it does need this impenetrable ice wall, meaning that there is no way to travel across Antarctica, that if you leave on one portion as you would on the earth you will not come back around the other side, that you simply cannot travel this as it becomes more and more impenetrable as you get deeper into the world. Now, let's look at some of the evidence for a spherical earth and some of the things that we're going to look at, and this is not a total, this is not every possible example. I just wanted to go over several different things that we could look at for the fact that the earth is spherical. We can look at things like observations from spacecraft. We can look at lunar eclipses, the eclipses of the moon. And we can look at observations of the stars and the constellations. We can look at some other observations, the sun, time zones, shadows of the sun, seasons, a few other things we can look at. And then finally we can look at gravity. Now there are a lot more than these. I'm not going through every possible argument and trying to demonstrate or refute every possible argument that comes forward. I simply want to look at some of these and give an understanding of them. So let's first of all look at what observations we have from spacecraft. This is some of the most direct evidence. First of all we traveled to the moon back in 1969 and images will show that the earth is spherical. The astronauts could watch the earth rotate. So you could see it going through different sections. We could see the different parts of it. We could see that the earth was clearly not a flat disc. We also have images from the International Space Station. So when we look at those we cannot see the entire earth from the International Space Station. It is in a low orbit. But you can see the curvature of the earth off in the distance. So we have some images like this where we can see the entire space station. And if you want to question how we could get an image like that, well this was taken by one of the shuttles that was either arriving or leaving the space station. So as it was near the space station looking back and able to get an image of it from earth. Now this is really some of the most direct and distinct evidence that we have that the earth must be a sphere. However, the argument of the flat earth group would be that space flight is impossible. So everything like this is fake. And everything that NASA does is a hoax. We've never been to the moon. We've never been up in space. The space station does not exist essentially. So it is an argument that essentially you have to accept to accept a flat earth is that everything that NASA has done is a hoax. Now certainly as an astronomer I don't believe that. So the evidence right here is sufficient for me to believe that the earth is spherical. But if we want to give that and start to look at that argument and not argue this point because if someone truly believes that NASA, everything NASA does has been fake for the last 60 years, then it's not something that you're going to convince them of. So we have to look at other arguments as well. So let's look at some of the other arguments that we talked about. And one of those is lunar eclipses. Well one of the arguments from the ancient Greeks was that during a lunar eclipse the earth shadow cast upon the moon is always observed to be circular. So when we look at the lunar eclipse we see the shadow being cast here. It is always a part of a circle. So we're seeing the earth shadow. The earth shadow is circular. Well a disk could cast a shadow that is circular. Only in certain orientations other times it would not be circular. It would be elliptical or it would be other shapes. The only object that will always cast a circular shadow is a sphere. So the Greeks knew that the earth had to be spherical simply because every lunar eclipse, the shadow was always circular. And what is the flat earth explanation? Well they call what they talk about a shadow object which is what is causing the shadow. So the shadow that we're seeing here in their argument is not the earth's shadow at all but some other mysterious unseen object that would be causing this. Now in order for this to be scientific it has to be something that we can test. So how can we detect this object? Certainly we can predict eclipses with very high precision based on a spherical earth and its orbit and the moon's orbit and the positioning of the sun. We can predict them down to the seconds. So the fact that there could be some other mysterious object, we have to have some scientific way of being able to test this. Otherwise it can be a belief but it's not something that we would consider science. Now we also mentioned that for example looking at the stars and the constellations can give us some ideas of the earth, the earth has to be spherical. And one common thing is that we see different stars when we travel to different locations on the earth. When you are far north you can see only certain constellations that are very far north on the celestial sphere. If you travel further south you start to see other stars that are not, would not be visible from that location. So it's a very easily explained in a spherical earth. We're only seeing a small portion of the sky. So from any given location we can see the half of the sky or so that is up above that. And we can't see anything that is down below. So for those of us in the northern hemisphere, stars near the south celestial pole are completely invisible to us. We never get to see them. However if you traveled along there down to South America you would then be able to see these. So that's one example of being able to see them. We can easily explain that in a spherical earth. We can also note that constellations in the southern hemisphere are upside down. If you've ever traveled south of the equator and looked for example at the constellation of Orion, which is one that is visible from both the northern and southern hemispheres, it is upside down in the southern hemisphere. And that is because of course you are looking from a different perspective. You are standing this direction instead of standing this direction. You are essentially upside down and therefore Orion is going to look upside down. Now how is this explained in a flat earth? Well they don't believe again. They don't believe NASA observations. So they argue that the stars are much closer and that you're not seeing the entire sky. So from our location here you can only see a part of the sky and on a flat earth if you traveled further along it you would be able to see different portions of the sky. They believe that the universe is much smaller than astronomers have been able to determine. The upside down appearance is just due to the perspective of motion. So if you are looking at something from one direction and you move to another direction things can change their appearance. So it's all a matter of perspective and things being a lot closer than astronomers will teach us. Now let's look at the sun and the flat earth. So in terms of the sun there are a number of different things that we can look at. Why would the sun first of all why would the sun not be visible to the entire earth? If the earth is flat then the sun is either up above the horizon and visible to everybody or it's down below the earth and visible to nobody. So why would it not be the fact that the sun is always visible or never visible? Well in this case they'd argue that the sun is really much closer than I will teach you. I'll tell you that the sun is 93 million miles away. They may argue that it's only a few thousand miles away and it's much closer and it's directed more like a spotlight. So instead of hitting the entire earth at once it would have a section that it is illuminating and as it moves around as it moves around here then you would have the different sections of this of the earth being illuminated at different times. Again that is against every observation that we have made but it does explain at least why the sun would not be visible at any given time. The other thing that we notice is that the length of daylight changes with the latitude. So during the summer we have longer days during the winter we have shorter days and we have different seasons. In this case again the sun is close enough but its pattern changes. So in the summertime it's actually a little further towards the north pole and making a smaller circle around here. In the winter it's a little further south and would make a larger circle around here. So depending on how you adjust the changing of that you can sort of make rather convoluted argument that the seasons could still be explained. So you can still do that but of course it's not as easy as explaining it with simply a tilted earth that can very easily explain the seasons. Now looking continuing to look at the sun we had a little more that we wanted to look at here and what we have is that shadows are different lengths. Well here's a very easy one sounds like it's very spherical. If the earth is a sphere then an object at this location would cast no shadow this on its passing straight down upon it whereas an object a little further north would be casting a slight shadow in this case seven degrees. This is the example of what Eratosthenes did in terms of measuring the circumference of the earth. So it's a very easy way to show that the earth must be spherical and telling us that even the ancient Greeks knew that the earth had to be a sphere. And again similar to the other one the flat earth explanation is that the sun is much closer than astronomers tell us. So we are making up essentially all these observations about the sun being 93 million miles away and it's only several thousand miles away and as you might imagine if something is much closer so if we have the sun much closer to us it could be straight overhead here whereas casting a shadow a little bit further away because of the perspective. When the sun is as far away as I will teach you it is then that would not be possible. All the rays would be coming in parallel and the difference is due to the curvature of the earth. So that explanation explains why the sun could not be overhead on one part of the earth but be overhead on another part of the earth. Now the last thing I wanted to look at here is how does gravity work on a flat earth? Well gravity would crush a disc earth into a sphere. So if gravity works as Newton and Einstein tell us the earth would have to be a sphere you could not possibly have a disc that strong. And that is part of the explanation those who believe in a flat earth believe that gravity is far worse far sorry gravity is far weaker than astronomers and physicists will tell you. So gravity is nowhere near as strong and therefore the disc does not get crushed. However that also causes another problem in that if gravity is not as strong how are we being held to the earth? And one of those is that what they believe is that first of all I said gravity is much weaker but the earth is accelerating upwards to simulate gravity. Now this is actually something given to us by Einstein. Einstein gave us the equivalence principle which says that there is no experiment we can do that would tell the difference between being on the earth in a gravitational field and being accelerated upward in a rocket. So if the entire earth were being accelerated upward how this could happen is very is nothing we can explain or test so again it's non scientific if it's not something that we can test. But there is honestly no way to tell the difference between these two situations. We also have to look at gravity always pulling down no matter where we are on earth gravity pulls down whether we're standing on the northern hemisphere or the southern hemisphere gravity always pulls towards the center and we again have to look at how that works in a flat earth. So gravity being much weaker and a flat disc accelerating upward could simulate gravity although imagining the immense energy needed to accelerate and to constantly accelerate the earth up through space is really difficult to wrap one's head around or to be able to explain. So looking at some of these you know what are some of the explanations well some of the explanations that they give they really involve a disregard for scientific observations. You pretty much have to believe that everything that NASA has given us over the last 60 years from launching satellites to launching space missions to the international space station anything else has been faked. Now to me that is very difficult to believe because that is not only NASA that is also the Soviet Union and Russian spacecraft but also now Chinese and Indian and other countries that have also set spacecraft into space and been able to see this so it is not just one organization that would have to be keeping this conspiracy together but it would be all of these and of course back in the 1960s this would be hard to argue that the U.S. and the Soviet Union who were admired in a deep cold war at the time would be able to agree to convince the rest of the world that the world was actually a disk that the world was not actually a disk but was really spherical that would have been a conspiracy among two very distinct enemies at the time and we also have to believe that all the measurements that I give you all the distances that I give you in this class are incorrect and fake so the things are actually much much smaller than we see here so let's finish up as we do with our summary and what we find is that again the flat earth proponents do make a number of explanations to explain how astronomical observations can be explained on a flat earth many of these will work but are also more contrived and difficult to explain and in some cases not possible to test and if you remember in a scientific theory in order to be a scientific theory it has to be testable we can make a great argument but if it's not something that could be tested it is not considered a scientific argument again most of these mean the complete disbelief of observations that have been made by NASA and measurements made by astronomers so we have to consider that all of this is fate has been faked and is a great conspiracy to convince people that the earth is spherical when it is actually flat and I will argue that the scientific evidence I've talked about some here we can look at other many others that you can look at as well it is really overwhelming so that I would argue that very clearly the earth is a sphere so that concludes this lecture on the flat earth society we'll be back again next time for another topic in astronomy so until then have a great day everyone and I will see you in class