Fusion reactions in the core of the Sun pump out more than two hundred trillion trillion neutrinos every second, and this number pales compared to the output of a supernova. Because of their numbers and their ghostlike nature -- billions pass through your body every second -- neutrinos may hold the answer to some of the most vexing questions of astronomy: why does the sun seem to produce far fewer neutrinos than our theories predict? Why is most of the matter in the known universe "dark" or invisible to our eyes? Where do cosmic rays come from? At the underground Sudbury Neutrino Observatory, these phantom neutrinos can be detected and studied.