  The Hubble Space Telescope (HST), in its thirteen years of operation, has
allowed us to observe properties of the universe humans have been able, until
very recently, to probe only with their thoughts. This review presents a brief
summary of a few of the highlights of HST discoveries, discusses their physical
implications, and identifies unsolved problems. A broad range of topics is
covered, from our own solar system to cosmology. The topics fall into the
general categories of: planets (including both in the solar system and
extrasolar), stellar evolution, black holes (including both of stellar-mass and
supermassive), galaxy formation and evolution, the determination of
cosmological parameters, and the nature of the recently discovered ``dark
energy.''
