Fred Whipple, astronomer at Harvard University.

Fred Whipple, astronomer at Harvard University
Fred Whipple, astronomer at Harvard University.
At lecturers held during the 1950s, Fred Whipple, an astronomer at Harvard University, passed on to students his impression of comets as 'dirty snowballs', which was certainly a common perception at that time, as researchers believed that comets were conglomerates of ice and carbon compounds.
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