 Greetings and welcome to the Introduction to Astronomy. In this week's Misconception in Astronomy, we are going to discuss the idea that people in the Middle Ages believed that our Earth was flat, and see that that is really not correct. So let's take a look at this. First of all, that was definitely not the belief among the educated people of the time. Now the common people who never went to school, never had any kind of education may have believed this, but the educated people would not have believed that the Earth was flat. And in fact, the spherical nature of Earth has been known for a very long time, going back to the ancient Greeks here. So the ancient Greeks knew that the Earth was round and were able to determine the size of the Earth. They measured Earth's circumference by looking at shadows that were cast at one location on the first day of summer. There was no shadow. On another location, there was a shadow. And that angle then told you what fraction of Earth's circumference these two locations were apart. So you could set up a ratio there and then figure out because you knew this angle. And if you could measure this size, you know that a full circle is 360 degrees. You could then find out what the circumference and therefore the radius with the circumference being equal to 2 times pi times the radius, you could then determine the radius of Earth. So the ancient Greeks knew this thousands of years ago. Now what there still was at the time was there was a debate as to the size of Earth. And the opposition to Columbus was based on this, not on whether the Earth was flat or spherical. Columbus believed that Earth was a lot smaller, so that he would be able to travel across and would not take as too long and would be able to bring sufficient supplies to get across the ocean to India. Now it was of course then found out others believed that the Earth was much larger. And not that Columbus would sail off the edge of Earth but would never be able to carry enough supplies to reach the land. So now today we can actually observe Earth from space. So we have things like images from the International Space Station very high up where you can see that there is a distinct curvature to Earth. So we can start to see the curvature here from lower level flights like the International Space Station. You cannot see the entire Earth at once, so you cannot see the entire spherical nature of Earth. However, if you travel a little bit farther away, let's say to the moon as we have done and look back, you can actually see the Earth off in the distance there. And here we see Earth as seen from the command module of one of the lunar missions. And what we see here is the lunar module in the same image. So as they had separated, then we could see both there and also looking off in the distance our own Earth very definitely a sphere. So let's go ahead and finish up with our summary here. And what we looked at here was the fact that the spherical nature of Earth has been known since the times of the early Greek philosophers who measured the diameter of Earth. Opposition to the voyages of Columbus was based instead on differing estimates of Earth size, not on any discussion of whether it was spherical or flat. It was whether the sphere was larger or smaller. And we looked at how we can easily see curvature of Earth from places like the International Space Station, and we can see the entire spherical Earth from lunar missions. So that concludes this week's Misconception in Astronomy. We'll be back again next time for another Misconception in Astronomy. So until then, have a great day, everyone, and I will see you in class.