Template:On This Day (nonfiction)/March 21
1768: Mathematician and physicist Joseph Fourier born. Fourier will initiate the investigation of Fourier series and their applications to problems of heat transfer and vibrations.
1884: Mathematician George David Birkhoff born. Birkhoff will become one of the most important leaders in American mathematics of his generation.
1924: Physicist Harry Lehmann born. Lehmann will contribute to the LSZ reduction formula and the Källén–Lehmann spectral representation.
1928: Charles Lindbergh is presented with the Medal of Honor for the first solo trans-Atlantic flight.
1965: NASA launches Ranger 9, the last in a series of unmanned lunar space probes.
2009: Mathematician Thierry Aubin dies. Aubin was a leading expert on Riemannian geometry and non-linear partial differential equations.