How do astronomers make sense out of the vastness of space? How do they study things so far away? Today Phil talks about distances, going back to early astronomy. Ancient Greeks were able to find the size of the Earth and from that the distance to and the sizes of the Moon and Sun. Once the Earth/Sun distance was found, parallax was used to find the distance to nearby stars, and that was bootstrapped using brightness to determine the distances to much farther stars.