April 22

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  1592: Minister, scholar, astronomer, mathematician, cartographer, and inventor Wilhelm Schickard born. He will design and build calculating machines, and invent techniques for producing improved maps.

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  1904: American physicist and academic J. Robert Oppenheimer born. His achievements in physics will include the Born–Oppenheimer approximation for molecular wavefunctions, and the first prediction of quantum tunneling. Oppenheimer will be called the "father of the atomic bomb" for his role in the Manhattan Project.

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  1953: Singer-physicist J. R. Oppenheimer performs his hit song "Destroyer of Worlds" at the Grand Ole Opry, leading to his being summoned before the House Un-American Activities Committee.

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  1954: Red Scare: Witnesses begin testifying and live television coverage of the Army–McCarthy hearings begins.

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  1970: The first Earth Day is celebrated.

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  1978: Optical fiber is first used to carry live telephone traffic.