US astronomer whose hypothesis in 1949 that the nucleus of a comet is like a dirty snowball was confirmed 1986 by space-probe studies of Halley's comet.

Whipple was born in Red Oak, Iowa, and studied at the University of California. He was professor at Harvard 1950-77 and director of the Smithsonian Astrophysics Observatory 1955-73.
In addition to discovering six new comets, Whipple proposed that the nucleus of a comet consisted of a frozen mass of water, ammonia, methane, and other hydrogen compounds together with silicates, dust, and other materials. As the comet's orbit brought it nearer to the Sun, solar radiation would cause the frozen material to evaporate, thus producing a large amount of silicate dust which would form the comet's tail.
Whipple also worked on ascertaining cometary orbits and defining the relationship between comets and meteors. In the 1950s he became active in the programme to devise effective means of tracking artificial satellites.