William Jefferys, Harlan J. Smith Centennial Professor in Astronomy at the University of Texas, Austin, and principal investigator of the Hubble Space Telescope Astrometry Science Team, has received the 1992 National Aeronautics and Space Administration Exceptional Scientific Achievement Award. He was presented with the award on March 27 at the Goddard Space Flight Center in Greenbelt, Md.

Astrometry, explains Jefferys, 51, is the "measurement of positions and motions of stars and other celestial objects." The classical method of determining the distances of stars is by measuring the parallax, or changes in the stars' apparent position owing to the Earth's motion around the sun. Ground-based telescopes, however, are hampered by the unsteadiness of the Earth's atmosphere, which adversely affects the accuracy of parallax measurements. The Hubble telescope, orbiting above the atmosphere, aimed to improve this accuracy.

While Hubble's much-lamented focusing problems have caused some delay in the astrometry project, Jefferys says...

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