Pluto Isn’t a Planet - Chris Lintott

00:00 // Introduction: Why Pluto Isn't a Planet 03:28 // Discovery of Uranus & a Mysterious Orbit 05:49 // How Neptune Was Found Through Math 08:16 // Percival Lowell's Hunt for "Planet X" 09:49 // Clyde Tombaugh Discovers Pluto (1930) 14:09 // A Brief History of Counting the Planets 18:02 // Pluto's Odd Orbit Raises Early Doubts 22:21 // The Kuiper Belt Theory Takes Shape 26:09 // Discovering Pluto's Moon, Charon 30:12 // Eris and the Rise of the Trans-Neptunian Objects 34:27 // The IAU's Chaotic 2006 Vote 42:43 // New Horizons: Pluto Up Close at Last 47:38 // The Verdict — Why Pluto Isn't a Planet Watch the Q&A session here:    • Q&A: Pluto Isn’t a Planet - Chris Lintott   In 2006, the International Astronomical Union adopted a definition of a planet that demoted Pluto to just one of what is likely hundreds of dwarf planets in our Solar System. Exploring the remote Kuiper Belt, this lecture challenges us to think about what kinds of scientific questions are worth our attention, what it means to name something – and why Pluto is worth caring about anyway. This lecture was recorded by Chris Lintott on the 3rd of June 2026 Professor Chris Lintott is a Professor of Astrophysics at the University of Oxford, and a Research Fellow at New College. Having been educated at Magdalene College, Cambridge and University College London, his research now ranges from understanding how galaxies form and evolve, to using machine learning to find the most unusual things in the Universe, to predicting the properties of visiting interstellar asteroids. He was the founder of the Zooniverse citizen science platform, which provides opportunities for more than two million online volunteers to contribute to scientific research, and which was the topic of his first book, 'The Crowd and the Cosmos’. His latest book is ‘Our Accidental Universe’. Professor Lintott is best known for presenting the BBC's long-running Sky at Night program, and as an accomplished lecturer. Away from work, he cooks, suffers through being a fan of Torquay United and Somerset cricket, and spends time with a rescued lurcher, Mr Max. He can often be found at the helm of Oxford’s science comedy night, ‘Huh, That’s Funny’. The transcript of the lecture is available from the Gresham College website: https://www.gresham.ac.uk/watch-now/p... Gresham College has offered free public lectures for over 400 years, thanks to the generosity of our supporters. There are currently over 2,500 lectures free to access. We believe that everyone should have the opportunity to learn from some of the greatest minds. To support Gresham College's mission, please consider making a donation: https://www.gresham.ac.uk/get-involve... Website: https://gresham.ac.uk X: https://x.com/GreshamCollege Facebook:   / greshamcollege   Instagram:   / greshamcollege   Bluesky: https://bsky.app/profile/greshamcolle... TikTok:   / greshamcollege   Support Us: https://www.gresham.ac.uk/get-involve...