Henrietta Swan Leavitt

Leavitt studied photographic plates of the night sky to determine the position and brightness of stars. Leavitt’s discovery led to an understanding of the Universe’s vast scale and allowed distances of the stars to be measured from Earth. How she changed… the world

Star snapshots

Born in 1868, Henrietta Leavitt studied astronomy before joining the Harvard College Observatory, USA. She analyzed photographs of the night sky, recording how bright each star was. In particular, she studied VARIABLE STARS – stars that vary in brightness. Leavitt calculated how long it took these stars to complete a cycle from brightness to dimness and back to brightness again.

The length of a Cepheid’s cycle predicts how bright it is.

The unsung astronomer whose work on stars led to a way of MEASURING the Universe

Stellar discovery

Focusing on a class of variable stars called CEPHEIDS, Leavitt noticed there was a direct relationship between the time it takes for a star to complete a cycle and how bright that star is. This is known as the period-luminosity relation. Using this rule to work out how bright a star is, scientists were able to calculate the distance of these stars from Earth.