Template:Selected anniversaries/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. He 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.
2016: Chromatographic analysis of Green Ring 2 reveals "at least two, possibly three" previously unknown shades of the color green.