Brian Marsden passed away on Nov. 18 after a prolonged illness at the age of 73. He was a supervisory astronomer at the Smithsonian Astrophysical Observatory at the Harvard-Smithsonian Center for Astrophysics (CfA).

“Brian was one of the most influential comet investigators of the 20th century,” said Charles Alcock, CfA director, “and definitely one of the most colorful!”

Marsden specialized in celestial mechanics and astrometry, collecting data on the positions of asteroids and comets and computing their orbits, often from minimal observational information. Such calculations are critical for tracking potentially Earth-threatening objects. The New York Times once described Marsden as a “Cheery Herald of Fear.”

The comet prediction of which Marsden was most proud was that of the return of Comet Swift-Tuttle, which is associated with the Perseid meteor shower each August. Swift-Tuttle had been discovered in 1862, and the conventional wisdom was that it would return around 1981. Marsden had a strong suspicion, however, that the 1862 comet was identical with one seen in 1737, and this assumption allowed him to predict that Swift-Tuttle would not return until late 1992. This prediction proved to be correct. This comet has the longest orbital period of all the comets whose returns have been successfully predicted.

Born in Cambridge, England, Marsden received an undergraduate degree in mathematics from New College, University of Oxford, and a Ph.D. from Yale University.

Marsden joined the staff of the Smithsonian Astrophysical Observatory in Cambridge, Mass., in 1965. He became director of the Minor Planet Center in 1978. Marsden served as an associate director of the CfA from 1987 to 2003.

To read the full obituary, visit the CfA.