Hello, I'm Chris Lintot, the 39th Professor of Astronomy here at Gresham College, and it's my delight to welcome you all to our Festival of Astronomical Ideas. Gresham, since its founding in the 16th century, has been about exchanging knowledge and sharing it with the widest possible group of people. And that's mostly what we're going to try to do in this festival, which is rather more informal than our usual programme of lectures and discussions. Of course, if you're in an organization that was founded in the 16th century, it's hard not to look back at history. And for those of us who are lucky enough to be professor of astronomy, the predecessor we point to is almost always the ninth professor, Christopher Wren, seen here in his pomp. Now, when I first came here, I started to wonder what Wren's lectures would have been like. What is this man, best known of course as the architect of the City of London after the Great Fire, as well as a few buildings in my hometown of Oxford? What's he talking about when he's talking about astronomy? Well, we know a bit of the instructions from the early days of the college. The astronomy reader, what we've now called the professor, is to read in his solemn lectures first the principles of the sphere and the theory of the planets, and the use of the astrolabe and the staff and other common instruments for the capacity of mariners. So the idea here that this is practical astronomy for a practical age. These are tools and principles that would be needed to navigate. London, of course, was a seafaring city connecting Britain to the rest of the world. And these are the things you'd need to know if you were going to deal in matters maritime. But it's also clear from the records that we have that Wren, and presumably his predecessors, didn't stick to the idea of giving solemn lectures any more than we do today. On the right is an illustration associated with a record of one of Wren's lectures in 1658, preserved in the archives of the Royal Society. What you can see here are his thoughts about Saturn. Now, at this point, this great planet was known not to be like the others. It didn't appear as a point of light or a sphere in the telescope. It had extensions that came and went over the course of many years. And Wren's 1658 lectures described what he called the handles of Saturn. And you can see here he's got this illustration of the planet held up by what we would think of as the rings, but here they're attached to the sphere. Now, the year later, in 1659, Huygens on the continent showed that this should be a ring system, that that would be stable. And Wren immediately says that he confesses that he was so fond of the neatness of this idea of Huygens and the natural simplicity of his contrivance that he gives up on his idea, though he does publish it later on, in part because a Frenchman sent in his own theory. Wren inspired a great rush of scientific activity. Friends of his who used to come to his lectures, and then we're told often to the pub, founded the Royal Society. And as Gresham, and this is the old college that you can see here, expanded. Later professors, Hook, for example, who's professor of geometry here, converted the college itself into a site of astronomical observations, cutting a hole in the roof and in several of the floors of the building to create an instrument 36 feet long to try and look for what we'd call parallax, for a measurement of movement that would give you a distance to a star. Here's an illustration of a later telescope, which was built at Greenwich at the bottom of the well to try and do this. And in fact, the monument in the city of London was built not just as a memorial to the fire of London, but as an observatory with a laboratory in the bottom and a hole in the top, used to try and look at stars as they passed overhead, but in effect, not successful. Partly because the stars were further away than anyone thought, but also because this is a terrible place in the middle of the centre of the commerce that was the city of London. It's a terrible place to put a laboratory. We can still do this kind of astronomy today. I really love this example, which I showed in one of my Gresham lectures a year or so ago. What you're seeing here is a view of two star fields as seen from Earth, and then alternately as seen from the New Horizons spacecraft, which is the one that flew past Pluto and sent back marvelous pictures of that icy world, which isn't a planet, but it's it's still interesting. You can see here that one of the stars blinks as we switch between these two perspectives, and these are nearby stars. We've got Proxima Centuri on the left, our nearest star other than the sun, and the star called Wolf 359 on the right. And from that blinking, because you can see them in different positions from two different locations, we can measure their distance. And so we finally managed to make this experiment. The fact that you can measure the distance of the stars, and the fact that most of the stars here don't change, even when you go way out past Pluto, gives us a sense of the scale of the universe. And when we think about our galaxy in this marvelous map from the Gaia satellite, or when we think about the universe full of hundreds of billions of systems, each of them like our Milky Way, containing hundreds of billions of stars. So you can see in this grand vista from the Vera C. Rubin Observatory, subject of a recent uh Gresham talk. Um, you somehow get this sense of overwhelming awe of being lost in a large universe, which astronomy can give you. And I think for a lot of people, when you think about the cosmos, when you think that we're on one planet around one star, which is one of a few hundred billion in a galaxy that's only one of a few hundred billion in this vast universe, it's very easy to feel small and to get lost. You either like that feeling or you don't. I have to say myself, when I've had a hard day at work or my email inboxes full or the stresses, I quite like being lost in the cosmos, but it's also, I think, a chastening reaction. But we can also find the familiar in astronomy. And I think that's important too. I like to show this slide, which is a terrible picture of the evening sky. You sunset has just happened. There is an evening star in the sky about two-thirds of the way across. It's a familiar scene. Something that you might see as you stumble out of the pub or walk out uh into your garden or walk home after work, even from a great city. Except in this case, when we zoom in on that star, it's actually double. There are two stars there, and that's because this is the Earth and the Moon hanging as a single point in a Martian night sky in an image taken by one of the rovers. And I think in this image, you get both halves of astronomy. It feels weirdly alien. We're seeing what Carl Sagan called that one moat, that one point of light on which every human in all of history has spent almost all of their existence reduced to being a dot. But on the other hand, it's just a landscape with a night sky above it. And when you look at the more spectacular images that are sent back by the Mars rovers, like this one from the Curiosity rover, this is an impossibly alien landscape. It's a place where no human has ever trod, where maybe there was life or maybe there wasn't, um, where the sky is an odd colour, where the rocks are an odd colour, where there's not a trace of vegetation. It's immediately unearthly. And yet, you can imagine walking through this. Friends who are rock climbers tell me that they immediately imagined how to scale some of the faces that you can see. I'm a walker and I can imagine how I'd meander through the valley on a day out. I can have this familiar relationship with the cosmos. And astronomy, I think, keeps going backwards and forwards between these two views. Of course, we've got Mars here, and Gresham has a long connection with Mars. It's not just Wren's view of Saturn. One of my predecessors was Colin Pillinger, who was the Gresham Professor in 1996, just before his Beagle 2 probe, seen in the top left here, being released from the Mars spacecraft that had carried it to the Red Planet, landed. And you can see on the right here a much later picture taken from orbit showing the dot that is the Beagle 2 lander. Now, Beagle didn't succeed. It was supposed to look for life on the surface of the planet, current life, a unique experiment. But it when it landed, it failed to unfurl properly and it didn't send a signal back. And Colin never managed to get a probe to Mars. But his work and his inspiration, including the lectures he gave here at Gresham, to inspire interest in this particular mission, have led to a new, more powerful mission, the Franklin Rover, built by the European Space Agency, constructed to a large part here in the UK, which will soon go to Mars and it will carry a drill to get beneath the surface and look for life, to answer this grand question and maybe make Mars feel a little more familiar. But I think when you think about this stuff, it's easy as an astronomer to just talk about astronomy. When I first came to Gresham, one of my colleagues told me that astronomy was easy, that the stuff we talk about, life, aliens, the Big Bang, galaxies, cosmic vastness, beautiful pictures. It's easy to get people interested in that. But actually, if you think about this mission, for example, this Franklin rover, which has landed on the red planet, which will land on the red planet, it involves a huge amount of physics. It's doing chemistry experiments. It's informed by astrobiology. But it's also the product of international collaboration between many different countries within the European Space Agency and many different agencies. It's a triumph of space law that we're allowed to do this. And in fact, the rover was delayed because it was supposed to be launched in partnership with Russia, something that became implausible and impractical, and indeed unwelcome after the Ukraine war. And so, just in any one of the stories that I've told, you see the connection between astronomy and all these other subjects. So that's what we're going to try to do today at this festival of astronomical ideas. You can think of it as Gresham, unplanned, unplugged, and a little bit remixed. Coming up, we've got Professor Milt Murmacades, the professor of music. He and I are going to be talking about the music of the spheres and some sonification. I'm actually not quite sure what Milt's got in mind. We've got Ronald Hutton, outgoing Professor of Divinity in digital form, talking about the strange history of archaeoastronomy here in Britain. And then later in the day, there'll be two discussion sessions myself with Vic Baines, former professor of IT, expert on cybersecurity. We're going to look at how the issues that we encounter when we think about communication and IT and electronics and the web and the internet here on Earth are extending outwards to low Earth orbit and beyond. And finally, I'm really excited to be talking to Helen Chersky, Gresham, Professor of the Environment and an ocean physicist about ocean worlds, both the ones I think about around the moons of Jupiter and Saturn, but also the one we live on, which Helen has explored and understood intimately. Hope you enjoy the day. This is the Festival of Astronomical Ideas.