Tracing the Universe's Most Abundant Atom with the World's Largest
  Filled-Aperture Telescope
  Among present-day observatories, the Arecibo Radio Telescope represents an
extension of Galileo's vision to its logical extreme. With a diameter of 305
metres and state-of-the-art instrumentation, Arecibo continues to build on its
legacy of world-class scientific achievement in radio astronomy. This paper
highlights milestones in the remarkable history of this telescope, and also
discusses current surveys that are imaging the hydrogen content of our Milky
Way Galaxy, and far beyond, in unprecedented detail.
