We spent the last couple of weeks talking about Mars, where there might be water on Mars. Where there, when there might have been water on Mars, where it's gone. Where it came from. We're going to now turn our attention to perhaps, the most fascinating planet in the solar system and I, and I say that because, well you just have to look up in the sky and you can see it. Go outside, just after sunset, turn in the direction of sunset and there'll be this bright object that's about midway up the sky and that's Jupiter. It's unmistakable, you can't miss it. If you think you've never seen Jupiter before in you life, go out tonight if it's not cloudy and you'll see it. And then I want you to do one other thing. If you can, I want you to get some binoculars. Take those binoculars out, steady yourself against a wall somewhere and see what you can see. It can be a little telescope if you have one, but actually, I don't really like little telescopes very much. I really like a good pair of binoculars just to see what there is to see in the sky. And if you do that, what you're likely to see is the exact same thing that Galileo saw in 1609 when he first turned his telescope to Jupiter. He realized that not only was Jupiter a disk, like this. But the, next to the disk were little dots and this is one night. He came back the next day and he saw, yes, the disk of Jupiter was still there. But there are now three dots, all in a line, but not where the other dots were before. He came back again. Couple of days later, disk dot, dot, dot. Some nights, there were three dots. Some nights, there were only two dots. Some nights, there were even four dots. And he very quickly realized he could connect the dots, each of these dots was a moon of Jupiter that was moving systematically outward. Systematically inward and going in orbit around Jupiter. Now did he know they were in going in orbit around Jupiter? That's the way we say it today. No, he knew they were moving back and forth across Jupiter. He knew that they were centered on Jupiter and he inferred that they went around Jupiter just the same way that the moon goes around the Earth. This of course was a major revelation, it was the first thing that you could confirm did not go around the Earth. The sun at that time, yeah, maybe it goes around the Earth. It kind of looks like it goes around the Earth, if you sit there and watch it all day long. Jupiter, okay. It goes around the earth, it goes on these funny epicycles in, in retrograde motions just like Mars that we talked about, but maybe it goes around the Earth. But these things, these four things did not go around the Earth. They very clearly were associated with Jupiter, a very big deal. Galileo couldn't see anything at all about the surface of Jupiter. He could only tell that there was this disk there that he could resolve, but nothing was on it. It took another 50 years of improvements in telescopes until people could reliably see features on the surface of Jupiter. And here's where some of those first reports were published in the Philosophical Transactions of the Royal Society in London in 1665, 1666 and the people writing in this are ingenious. Let's see what they have to say. The first is a report on an account of the improvement of optic glasses, also known as long telescopes and much of the detail is about how the optical quality is better, but then also on observing Jupiter, which appears to have certain protuberances and inequalities, which I think means its surface features. And he is now observing whether or not, they change their situation, which I think means, he's trying to determine if he sees features moving on the planet. In which case, you can say, Jupiter is turning upon his ax, turning on its axis, just like the Earth does, which would confirm the opinion of Copernicus. Copernicus was the one who said, of course that the Earth and everything else goes around the sun and not only that, that the direction, the Earth's rotation is the same as the direction of the Earth as it goes around the sun. And therefore, every other planet should rotate in the same way. Turns out that's not exactly true, but most of it's true. Even better though is right just an inch below is a spot in one of the belts of Jupiter by the ingenious Mr. Hooke, who may or may not go on to become Captain Hooke, I'm not sure. But he observed that there's a small spot in one of the belts of Jupiter and observing it from time to time to time, he found that within two hours, it had moved east to west about half a length of diameter of Jupiter. If that's the case, east to west half the length of diameter of Jupiter, that means something like a spot moving from here to something like here. That means something like a quarter of a rotation of the disk, which means something like Jupiter's rotating something like once every eight hours. It only took a few more years until the watching this spot, which turned out to be the great red spot, watching this spot rotate around. It had been determined that the true rotation rate of Jupiter is nine hours, fifty minutes. And that indeed, just like the Earth, it rotates in the same direction, then it goes around the sun. For the next 200 years, observations were purely visual. People would look and try to time when the great red spot was going across or whatever features they saw or they would make drawing sketches like this one by Captain Noble, published in the Monthly Notice of the Royal Astronomical Society, volume 40 in 1879. The monthly notices are still an important astronomical journal that astronomers read today. This is a pretty spectacular drawing. Here's the great red spot. And the great red spot is in the southern part of Jupiter, but because telescopes flip the image, they would always draw them up like they saw them and the bands are clearly visible. Occasional other spots are visible, like this white spot. It was thought at least by Captain Noble here. That the dark regions around the white spots were actually shadows caused by these white clouds high up above the actual of Jupiter. This turns out not to be true. But otherwise, it's a pretty spectacular drawing from an age just when people were trying to get their first glimpses of what was on the surfaces of planets. If you look carefully, 1879. This is right around the time Schiaparelli, the, the were making the drawings of the surface of Mars. The ideas that these planets were places that you could learn about was really coming into existence. Of course, soon thereafter, there's the explosion of photography and the belts and all the other cloud features are discovered. And we don't need to go in detail through the increasingly better pictures that we could see of Jupiter as time goes on. Let's just jump to the best. This is a movie made by the Cassini spacecraft. The Cassini spacecraft was on its way to Saturn, but to get to Saturn, it got a gravitational assist from Jupiter. So, it flew by close to Jupiter, took some nice pictures as it went. And over about ten days as it was approaching, it took this movie of the entire surface and you can imagine this is the surface unwrapped. And indeed, you see that great red spot now correctly put on the south like it really is. You see white spots with things that are not shadows around them that are below the red spot. You see zones and bands. You see occasional storms erupting here in the middle. Watch these little white spots right there. Erupt go away. Erupt go away. You see strange dark spots appear down and through here. These strange dark spots are actually shadows of the satellites going across the surface. The sha, shadow, shadows were actually observed in the, in the 1670s and that's the way people knew for certainty that the satellites were in orbit around the planets. And you see the satellites themselves every once in awhile, appearing down through here. It's a spectacular view of a spectacular planet and as the views of Jupiter were getting ever better as the, the cloud systems were being discovered, it was, was realized that it was a complete, the giant planet completely enclosed in clouds. It had to have begged the question, which is the question that we're going to spend the rest of this unit exploring, which is what is underneath those clouds in this biggest of planets in the solar system?
