February 20

1844: Ludwig Boltzmann, after whom the Boltzmann constant (1.3806505 × 10^-23 J/K) was named, was born. 1877: The first cantilever bridge in the U.S. was completed in Harrodsburg, KY. 1931: John Milnor, who proved that a 7-dimensional sphere can have 28 different differential structures - important work to be sure - was born. 1948: The first B-50 Superfortress bomber was delivered to the Air Force. 1956: German physicist Heinrich Barkhausen, who discovered the effect named after him regarding changes in the magnetic domain properties of metal, died. 1962: Astronaut John Glenn became the first American to orbit Earth as he flew 3 times around the earth aboard the Friendship 7 Mercury capsule. 1965: The Ranger 8 spacecraft crashed on the moon after sending back thousands of pictures of the lunar surface. 1986: The Soviet Union launched the Mir space station into orbit. 1993: Ferruccio Lamborghini, of sports car fame, died. 2005: Spain became the first country to vote in a referendum on ratification of the proposed Constitution of the European Union.