He walks through the first ten asteroids ever discovered, placing them in order and comparing their sizes to Earth's moon. Ceres, the largest, is technically a dwarf planet now. Vesta comes in as the second largest with a diameter of 326 miles, discovered by Heinrich Wilhelm Olbers in 1807. The others, Pallas, Juno, Astraea, Hebe, Iris, Flora, Metis, and Hygia, range smaller but still represent the foundational discoveries that opened up our understanding of the asteroid belt. When you see them all lined up to scale against the moon, you get a sense of just how much material is floating out there between Mars and Jupiter, and how recent our awareness of it really is.