All right, Tycho Brahe. This is a quote from the best biography we have of him. I'll pass around two biographies. One of them is not really a biography and the first one is the late Victor Thoren's biography managed to finish it before he died, and the other one I'll start it here is just an account of what happened on Tycho's island Hven.

So, with Tycho that the current view is that this is where modern astronomy begins. In some ways it's even where modern science begins and I'll explain that in a moment. Tycho came from a very wealthy, noble family in Denmark. Good ties to the king, etc. He got interested in astronomy when he witnessed in 1572, a supernova.

We now know what a supernova is. They had no idea where supernova was but all of a sudden there was a star that was never there before and it was very, very bright which violates aristocracy and principle that the celestial realm never changes, etc. That got him fairly interested in astronomy and what he managed to do was to persuade the king of Denmark to set aside an island for him.

It was an island on which people were already living, by the way. Set aside the island of Hven, H-V-E-N, not too far off the coast from Copenhagen, which I hope you all realize is very far north and nice and cold. Give him this island, and give him enough money, to build, well, in effect, an observatory, that's a great understatement.

I'll come back to that in a moment. Build that and hire people to work there including the people who are already living, but bringing people from abroad. He called the place Uraniborg after the God Uranus. And, from 1576 when he first moved there, he did observations for 20 years.

What finally ended the observations was his king died, a 16-year-old king replaced him, and the powers that be in Copenhagen, especially at the university, convinced the 16-year-old king that he was wasting all his money on Tycho, down on this island. He should withdraw all support, in a sort of classic, internal, academic move that put the people at the university convinced withdraw support, at which point he blew up, destroyed most of his equipment, looked for a new place to go, ended up in Prague and then died in 1601.

He's important for two reasons. In 1577, he looked at a comet, paid a great deal of attention to it and ended up concluding, rather importantly, that and Michael Maestlin was the other half of this, that if you do parallax, that if you observe that comet from two different places sufficiently far apart on the Earth.

He conclude that the comet is passing through the orbit of Venus which of course among other things, means there's no crystalline sphere out there. And also, one of the first proposals that comets are not an atmospheric phenomenon. And to show you how radical of a proposal it was, Galileo died believing comets are an atmospheric phenomenon, not a celestial phenomenon at all.

That's why there's no mention of comets in the Almagest, or in Copernicus. They weren't considered astronomical, celestial phenomenon, and Tycho and Maestlin together are fairly significant in that. They took years, he working with Maestlin and others, looking at other people's observations. It wasn't till 1588 that he published a book on the comet.

And in that book, he proposed a new system. So I'll let you read Thoren's, well, it's worth reading. For as long as histories of astronomy have been written, heliocentrism has been regarded as the hallmark of modern astronomy. In accordance with this tradition, Nicolaus Copernicus, as the effective originator of the heliocentric doctrine, has been hailed as the Founder of Modern Astronomy.

In fact, however, except for the motion of the Earth, the revolutionary element in Copernicus' work is very small. In most respects his De Revolutionibus follows Ptolemy's Almagest so closely that he can equally well be regarded as the last great practitioner of ancient astronomy. On this view, it was the 70 year period following Copernicus' death in 1543 that actually saw the transition to modern astronomy and in so far as any such development can be attributed to the influence of one person, that transition was wrought by the ideas and efforts of the Danish astronomer Tycho Brahe.

Now, that's the biography of Tycho Brahe, right, so obviously it's. But I included it partly simply to say it's not me, it's not Swerdlow, it's not Neugebauer who's saying Copernicus is from another era. It really is a consensus now that Tycho is the. I'll give you a couple of reasons why Tycho is so important, but let me just start with one thing.

He's one of the first people I can identify who really is committed to the idea that on every empirical question, the empirical world is the final arbiter. No bibles, no other authorities, no philosophers, you've got to find some way to make the empirical world in final arbiter. And that's a hallmark of modern science, it's extraordinarily hard to do.

And others gave lip service to it. Galileo constantly said that, and when you look at his arguments and the empirical world is not always the ultimate arbiter. But several people were deeply committed to that, Tycho was high on the list. The highest on the list I assure you was Isaac Newton.

Let's start with his system. The system is one that we've already described, the sun goes around the Earth and all the planets go around the sun. It was the intermediate step that Copernicus reached that I described to you when I had that diagram of up. And you can see unfortunately, the Earth Sun orbit intersects these things.

But what persuaded Tycho that this is okay, was that comet passing through the spheres. So, he simply decided there are no spheres. And it's dramatic, and I'm throwing this partly at Michael, it's dramatic because he throws out a 2,000-year old cosmology, the only one we have, replacing it with nothing.

So much for cosmology being important to astronomy. He simply dropped the whole issue. And that's an example of his wanting the empirical world to be the final arbitrary. He wasn't gonna let pretty cosmological pictures interfere. But, his argument ends up, there are two-fold argument, but the main argument is comets.

He has a second argument about Mars coming closer to the Earth than the sun, but that's only an argument against Ptolemy. Let me talk some now about him and his observatory. This is him with his mural art. He's legendary for having a wooden nose, having had his nose clipped off in a dueling exercise.

So, he was a difficult human being, very domineering. I can imagine what the poor people living then were like. But he was also profoundly committed to doing observations extremely well. So he designed instruments, they are naked eye instruments. They don't use lenses but they are very carefully done, constantly checked, protected against thermal distortion and things like that, with cross checks in them, there's a whole series of them.

Instruments have been used from Ptolemy forward. These are just much more sophisticated. At Uraniborg itself, he creates observatories. The one at the top is the initial one. I think the one below, he actually put the observers below ground with walls around them, and holes from which they looked to protect them against wind.

He used fires to try to keep temperatures halfway reasonable. He would have multiple observers look at the same thing, and he would cross check one another against them. This is just a little of what he did. Let me describe it slightly differently. This is the first major research institute.

Here's what he had. He had his observatory in his palace where he lived. If you look carefully at the Christiansen biography the second half of it is the people who came and worked with him for a year or two, or a month or two and then went back to the rest of Europe, it's like 90 people.

The practice of astronomy that he did at Uraniborg spread throughout Europe with the standards of very high precision observation, thanks to him. So, those people had to be kept up so he had dormitories for them. He had dormitories for his full-time observers. He had to have the instruments made so he set up an instrument factory as part of it.

He had to publish things which means he had to have paper and a printing press. So he formed a paper making factory there to produce their own paper, and a printing press to produce the results. Everything was on the island. Everything he needed. The only thing he needed that wasn't on the island was good observers and he would invite them to come, put them up, wine them and dine them, and have them working with him at some substantial length.

So what came out of this? And I'm running out of time but I want to save the last five minutes. What came out of this was the first body of observations at a number one, at a high standard of observational accuracy. But almost more important than that, how to uniform high standard.

That is, you knew for the observations that all but occasional ones were gonna fall within a definite amount. That's better then just knowing there's high precision because you can generally bound what the error is and he knew that and he put a good deal of effort into it.