This episode explores the ingenious methods used throughout history to measure cosmic distances, a journey from understanding the scale of our solar system to mapping galaxies across the observable universe. Against the backdrop of Kepler's work on planetary orbits, the discussion pivots to the clever use of parallax—measuring the apparent shift in a celestial object's position from different viewpoints on Earth—to determine distances to planets like Venus. More significantly, the episode details how Romer's observations of Io's eclipses by Jupiter provided the first measurement of the speed of light, a crucial element in later distance calculations. For instance, the challenges faced by early astronomers in achieving the necessary precision for parallax measurements are highlighted, emphasizing the ingenuity of their methods. The episode then moves to measuring distances to stars using parallax, employing Earth's orbit as the baseline, and introduces the Hertzsprung-Russell diagram and Cepheid variable stars as tools to measure distances to more distant objects. Finally, Hubble's law, relating redshift to distance, is explained as a method for measuring distances to the farthest galaxies, culminating in a visualization of a portion of the universe based on data from the Sloan Digital Sky Survey. This reveals the large-scale structure of the universe and ongoing efforts to refine distance measurements, highlighting the ongoing evolution of our understanding of cosmic scales.
