This episode explores the historical methods used to determine cosmic distances, from the size of the Earth to that of the universe. Against the backdrop of renowned mathematician Terence Tao's childhood fascination with astronomy, the discussion delves into the ingenious techniques employed by ancient Greek scholars. More significantly, the conversation highlights Eratosthenes's calculation of Earth's circumference using shadows and the distance between two cities, and how lunar eclipses were used to estimate the Moon's distance and size. For instance, the use of lunar eclipse duration and the Moon's orbital period to calculate the Earth-Moon distance is explained. The discussion then pivots to Aristarchus's attempt to calculate the Sun's distance and size, revealing the limitations of his technology and the resulting inaccuracies. However, his work, despite its flaws, was crucial in proposing the heliocentric model. Finally, the episode culminates in a detailed explanation of Kepler's groundbreaking work, which involved cleverly using the periodic return of Mars to deduce the shapes of planetary orbits, a feat Einstein himself called "an idea of pure genius." This showcases how even with limited technology, brilliant reasoning and meticulous data analysis can unlock profound cosmological insights.
