It seems likely to me that anybody who had one of the early telescopes would have taken it and pointed it up to the sky and looked at things like the Moon, and Jupiter, and Venus, and, of course, at Mars. But those early telescopes really didn't show much. Perhaps one of the first astronomers to take a good look at Mars and, and see surface features and understand something was going on was Giovanni Cassini. Cassini is famous these days because he also observed things like, the, the gap in the ring of Saturn. It's called the Cassini Division, and one of the reasons why the Cassini spacecraft, which is going around Saturn right now, was named after Cassini. But Cassini, looked at many things in the solar system, many things in the whole sky. And one of the things that he should be more famous for is being the first to really determine the rotation period of Mars. Now how would you determine the rotation period of a planet? It's pretty simple in those days. You watch it, and you can see that something is on the surface even if you don't know what it is. You see something on the surface changing, and then you realize that it repeats with a certain time period. Cassini watched Mars night, after night, after night, and he realized that if he looked, if he looked at the same time every night, the same surface feature wasn't on Mars. But if he looked 40 minutes later, every night he could see the same face of Mars. Now he didn't have a very good view of Mars, but it was just enough to be able to say that the rotation period of Mars was something like 24 hours and 40 minutes. It's really quite remarkable. I think that people must have been fairly astounded that the rotation period of this planet was so very similar to that of the Earth. With a little more careful observing, it was realized that not only do you see the same spot reappear to time and time and again 40 minutes later every time, but actually you could see the direction that the features were rotating. And they weren't rotating perfectly aligned north-south, they were actually tilted. In fact, they were tilted by about 25 degrees, 25 degrees is the obliquity of Mars. The obliquity of the Earth as you remember is 23.5 degrees and again, you remember that that means that the Earth is tilted from straight up and down north south by 23.5 degrees. The sun is over here and north-south, the definition of what is exactly north-south in this case is with respect to the orbit of the earth. So when the earth's North Pole is tilted toward the sun, its Northern Hemisphere summer and when the earth rotates all the way around to the other side and the South Pole is pointed towards the sun, its Southern Hemisphere summer. Mars is the same way, it's just a little bit more tilted. So it's a little bit longer of a period, it's a little bit more tilted, it's a little further away. Staring at Mars, as people were through their telescopes the next, I think, very exciting development was the realization that not only are there sort of odd modeled features on the surface of Mars. But if you looked carefully, at the North Pole sometimes at the South Pole, you would see little white spots. I think the best way to demonstrate this is to show you what these look like in a small amateur telescope today, just sort of similar to the view that they must have been getting back in the biggest telescopes in the 18th century. Here's an image taken of Mars recently by amateur astronomer Tom Ruen from his telescope in Minnesota, six inch telescope and you can see a couple of interesting things. You see these sort of mottled surface features that I'm talking about. Nothing really distinct, nothing that you can look at and say, oh yes, there must be continents, seas, forests, but the one distinct thing that you see is this white spot, right there. It's the most distinct thing that you see on the surface and it is distinctly at the North Pole in this picture. Sometimes, depending on where the Earth is relative to the, to Mars and what kind of view we get, you see them on the South Pole instead. I want to give you a feel for what the entire rotation of Mars looks like and I'm going to show you again images taken by Tom Ruen. I'm going to show you this straight off the Wikipedia page, because it's actually a very nice view of what Mars looks like. There is the image that we just saw, right there. There's the polar cap. And here's an entire rotation of Mars. You can see these albedo features rotating around in this direction. You can see that north polar white cap staying in place the entire time. And the one other thing you can see in this series is that Mars gets a little bigger and a little smaller. Because this was taken over the course of an entire season as different views of Mars could be seen at different times of the night. One other thing that's worth noticing is, as it points out here, this is the true color. The one that I showed you a minute ago is really how it would look if you were looking at it with your eye in a telescope. And this one has been enhanced to show the contrast a little bit better. And so these very nice contrast features, though real, you'd have a really hard time discerning with your eye. But I still, I want you to look at this for a minute. And think about how amazing this must have been back in the early days of the telescope to realize that there is this round world like the Earth that has a similar day to the Earth, a similar tilt to the Sun of the Earth and most astoundingly it has these white spots at the north pole. White spots at the north pole, what could they possibly be? They have to be polar caps, right. It seems pretty obvious that you would see these and immediately declare these to be polar caps. You could imagine with all of these things and with these new discoveries you could imagine why people's imaginations would immediately leap to the idea that Mars must be a place that could be, should be inhabited. These ideas lead to the fun part of today's story which was the early belief that not only was there life on Mars but there was life on Mars that had constructed large scale canals on Mars. Where did these beliefs come from? Well, in the, the late 1800s, there was a particularly good apparition of nars, Mars. Apparition meaning that Mars was particularly close to the Earth when the two of them were at opposition. During this time period, people got their first really good look at the surface of Mars and started to make the first detailed maps of what's on that surface. One of the best early ones was from Schiaparelli, 1888. He made this very beautiful map which I'll show you in a minute is not a bad map of what he's seeing on Mars. He didn't really talk about what any of the features are. All he really knew is that there were bright spots and there were dark spots. Do notice though, he called this dark region in the south, Mare. Mare is the same word that was used at the time for the dark regions on the moon, which means sea. There were times when people actually thought that the dark regions on the moon were waters and, and perhaps, that was the thinking that was going along in through here too. Schiaparelli called these channels through here, as he called them channels in Italian, canali and, and people speculate that this was the origin of people starting to think that these were canals on Mars was a misinterpretation of this word which really means something more just like channel. How good was Schiaparelli's map of Mars? Well, let me show you how it looks compared to a modern image of Mars. Okay, here's the same map, but now with Mars on it. Hellas, this region called Hellas right here is in fact now what we know as the Hellas basin on Mars, a large impact crater, is there a canal down the middle of it? No, but Hellas is definitely there. You can see the dark regions up through here, or these dark regions up through here. This, this little block in here, Chryse, we still call these regions by their same names. People who study Mars will recognize all of these names. Tharsis, Tharsis, this region of Tharsis is the region of the large volcanoes. These are the large volcanoes on Mars that we'll, we'll talk about. And this dark southern sea is what we now know to be the dark heavily cratered southern highlands. So Schiaparelli was generally correct about what was going on. He didn't have too many things that we might think of as made up in there every feature. There were small scale things like the, the, the bifurcation of Hellas basin and the fact that they, he thought these are lines in through here. You can sort of see where perhaps those things come from these features are sort of like these features. All of those are really in there. He really was trying to be, it seems like a faithful recorder of what was really there. The idea that there were more than just obscure surface features there was really pushed by the American astronomer Percival Lowell who used his own telescope and in fact founded his own observatory. And looked at these features on Mars and drew his own maps. His maps looked more like this. And where Schiaparelli saw features that were maybe channels, that were maybe just albedo features, Lowell was convinced that he saw all of these very straight, very narrow features on crisscrossing Mars. This is similar view to what we just saw before. In fact the Hellas Basin is this region right down through here. This was a time when the northern hemisphere was more in view than the southern hemisphere. These dark regions are similar to the ones that we just saw in Schiaparelli's map. But Schiaparelli didn't have any of these really long straight lines in through here. Not only did Lowell think that he saw canals on there. He also called these black dots that he's drawn in through here oases. And note that every time a canal intersects another canal, it's because they're going to these oases. By this time, people realized that this region around here was not a sea. The way they could tell it was not a sea was because they could see features on the sea that rotated. So if you were looking at just an ocean, it would be a pretty uniform view. And they could see these repeating rotation, after rotation, after rotation. And, in fact, most people at this point thought that Mars was essentially desert-like and didn't have big bodies of water on it. So Lowell's idea was that these canals were the product of people living on a dying planet, and these canals were going from the North Pole. All of the water that was left on the planet Mars was trapped up here in the North Poles. And people had built canals to bring the water down to these oases where they actually lived. This led to, in 1911, the publication of Lowell's book, which has a nice, simple title by Percival Lowell. But my favorite part is that I'd like to someday publish a book where I have this many things in my description of myself, director of the observatory, non-resident professor, fellow of the American Academy of Arts and Sciences and many, many more. I think the reason for so much stuff down here is to bolster the claims that this is real. He didn't have to bolster very hard because people loved the idea that Mars was perhaps inhabited. They loved it so much that he and his ideas appeared in the New York Times, not under the headline that you might think, is there life on Mars, but in fact, there is life on the planet Mars. Absolutely, there are the canals, there are the oases, there is the shepherd looking at Mars for no apparent reason. Was the idea crazy? No, the idea wasn't crazy. There were good reasons to be interested in the question whether or not there was life on Mars. Are there canals on Mars? No, there aren't canals on Mars. Are there things on Mars that plausibly look like canals through telescopes of the size that Lowell was looking through? No, there aren't even things on Mars that plausibly look like canals. So what was Lowell seeing? Well, I've, I've heard some explanations such that maybe he was looking at the, the blood vessels inside of his eye. He might have experienced something like this. You look through a microscope and rather than seeing the thing you're supposed to be seeing in there. You start to see in some weird seeming way the inside of your eye, the blood vessels there through reflections in the optics. Maybe something like that was happening, but, but Lowell wasn't seeing the same pattern again and again. He was seeing a rotating pattern. He was seeing something that rotated every 24 hours and 40 minutes with these canals on it. I don't think the blood vessels can explain something like that. I've also heard an explanation that, oh, it's just a typical type of optical illusion that you have dark patches here and, and bright patches here that that your eye, if it doesn't quite have the resolution to see it, makes these very linear features like that again, optical illusions. I think other people should have been able to see it. I really think that there's, there's very little argument to be made, except that this was sort of wishful thinking on Lowell's part. He really wanted there to be some sort of civilization on Mars. And liked the idea that these were canals, and that there were oases, and that there was a society that had figured out how to survive in the, in the wake of all this disaster. The disaster unfolding at the time here was the, was World War I impending. And I think the idea that, that people could live together peacefully was, was a very compelling one. But there is no actual evidence or even really good reason to think that you should be able to see or even think you see these sorts of features on something like Mars. In the next lecture, we will move into what I think of as the, the pre-modern era. This is sort of the historical era where people were just beginning to try to understand what was on Mars. In the, in the next 50 years after Lowell's splash with canals on Mars, people really started trying to apply the tools of science to understand what was really going on, on this planet next to us that looked so potentially like our own.
