July 04 – Birth of Henrietta Swan Leavitt (1868)

American astronomer Henrietta Swan Leavitt, the woman indirectly responsible for making Earth a much smaller and less important place,was born today in 1868.

Leavitt worked at Harvard College Observatory as a “computer”, measuring and recording the brightness of stars. She worked on variable stars in the Magellanic Clouds, and noticed that the luminosity of a star and its period were linked. This discovery, the period-luminosity relationship , eventually led Edwin Hubble to the conclusion that spiral nebulae are actually galaxies, thus making the Universe a whole lot bigger, and showed Harlow Shapley that the Sun is in the galactic suburbs, and not, as had previously been suspected, at the centre of the action.