Day is President Emeritus of San Diego State University (SDSU). He served as President of SDSU from 1978-96. He was a professor of physics at the University of Maryland from 1964-1978. Day received a Ph.D. in Physics from Cornell University, 1957.

Dr. Day has published widely as a theoretical physicist and as an experimental high-energy physicist. He is a former member of CCST's Board of Directors, and has served as National Science Board Member, 1985-1996; National Science Board Vice Chair, 1988-94; member of the President's Committee on the National Medal of Science, 1983-85; member of the Advisory Group, Subcommittee on Science, U.S. House of Representatives Committee on Science, Space and Technology; State Representative, American Association of State College and Universities; and delegate, Commission of the Californias, Education Committee.

His Honors and Awards include the SDSU Alumni Association's Lifetime Achievement Award, 1996; the International Citizen Award, 1992; the Rev. John J. Cavanaugh Award to the University of Notre Dame alumnus for distinguished public service, 1991; elected to Fellowship in the American Physical Society, 1968; the University of Notre Dame, Science Centennial Award, 1966; and the Maryland Academy of Sciences "Outstanding Young Scientist" Award, 1963.