William Markowitz

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William Markowitz (February 8, 1907 - October 10, 1998) was a Polish-American astronomer, principally known for his work on the standardization of time.

His family were Polish and his mother was visiting Mlec, Austria when William was born. The family emigrated to the USA in 1910 and settled in Chicago, William earning his doctorate from the university in 1931, under W.D. MacMillan. He taught at Pennsylvania State College before joining United States Naval Observatory in 1936, working under Paul Sollenberger and Gerald Clemence in the time service department.

Marrying Rosalyn Shulemson in 1943, Markowitz eventually became director of the department and developed ephemeris time, proposed by Simon Newcomb in the 19th century, as an international time standard. He subsequently worked with Louis Essen in England to calibrate the newly developed atomic clocks in terms of the ephemeris second. The fundamental frequency of caesium atomic clocks, 9,192,631,770 Hz, which they determined, has defined the second internationally since 1967. At the International Astronomical Union (IAU) meeting in Dublin in 1955 he proposed a system which remains today.

He served as President of the IAU commission on time from 1955 to 1961, and was active in the International Union of Geodesy and Geophysics, the American Geophysical Union, and the International Consultative Committee for the Definition of the Second.

After retirement in 1966, Markowitz served as professor of physics at Marquette University until 1972, and also held a post at Nova Southeastern University. He died in Pompano Beach, Florida

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