Tuesday, August 31, 2004

Fred L. Whipple

A great man died yesterday at the grand old age of 97. Fred Lawrence Whipple was born in 1906. He joined the Harvard College Observatory (now the Smithsonian Astrophysical Observatory) and in the early 1930s, he became interested in meteors, working on determining the orbits of meteors, using multiple station photography using cameras outfited with a rotating shutter. Using parallax to measure the spacial location of a meteor imaged by two cameras several miles apart, and by measuring the rate of motion of the meteor by measuring the distance traveled between shutter interruptions in the trail, he was able to determine the location and velocity of meteors and thereby, their orbits. Prior to his work, other observers had found that a large number of meteors they had observed resulted in hyperbolic solar orbits. Whipple even modeled an extra-solar origin for some of these hyperbolic meteors. However, Whipple found that he needed to accurately time the appearance of the meteor for the orbit he got varied considerably from hyperbolic to elliptical depending on when during the long exposure that he assumed the meteor had appeared. Once he accurately timed the appearance of a number of meteors, he found that none of them were hyperbolic!

Whipple became interested in the physics of meteoroid ablation and atmospheric drag. This work led to a study of cometary nuclei which ultimately led to his revolutionary and still widely accepted "Icy Conglomerate" model of the comets nucleus - the so called "dirty snowball". His landmark paper in 1950 along with a paper by Jan Oort on the distribution of orbits of the long period comets in the same year completely changed our view of the comet complex and of the origin and evolution of the solar system.

Whipple had the foresight prior to the 1957 launch of Sputnik to set up a network of cameras that ultimately were used to track the first manmade Earth orbiting satellites. In 1972, "The Collected Contributions of Fred L. Whipple", a two volume collection of all of Whipples publications up to that point was published. These two volumes are each nearly 1000 pages long and are still an important collection, more than 70 years after the first of Whipples publications.

I have fond memories of meeting with Fred Whipple in about 1995. We chatted for perhaps an hour and he happily autographed my copy of the first volume of his Collected Contributions and also gave me an autographed stamp from the Republique Islamique de Mauritanie which honors him. We also talked at length about some of my work on comet photometry. We will miss Fred L. Whipple.



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