April 24

1914 – "The Franck–Hertz experiment," a pillar of quantum mechanics, is presented to the German Physical Society.

• This experiment was the first electrical measurement to clearly show the quantum nature of atoms, and thus "transformed our understanding of the world".

1967 – Soyuz 1, launched the previous day, crashes. Its occupant (Vladimir M. Komarov) becomes the first spaceflight fatality.
1970 – The first Chinese satellite, Dong Fang Hong I, is launched.
1990 – The Hubble Space Telescope is launched by NASA.
2007 – Planet "Gliese 581 d" discovered in Chile, and believed to be a planet capable of holding extraterrestial life.