Astronomer. Born in
1926, he studied at the
University of Illinois, the
California Institute of Technology, and the Observatories of the
Carnegie Institution of Washington where he was a
graduate student under
Edwin P. Hubble. He is best known for calibrating
Cepheid variable stars, or
standard candles, to estimate the value of the
Hubble constant. He now uses the
Hubble Space Telescope to determine the distances to distant galaxies.
He is also known for discovering
quasars,
blue straggler stars and his intense observations of
globular clusters with
Martin Schwarzschild.