Leavitt, Henrietta Swan (1868-1921), was an American astronomer. Her work helped later astronomers establish the present scale of the size of the universe.
Leavitt became famous for her study of Cepheid variables in the galaxies called the Magellanic Clouds. A Cepheid variable is a type of star whose luminosity (brightness) changes regularly with time. The period of such a star is the time its light takes to change from bright to dark and back to bright. Leavitt discovered that stars with longer periods had greater average brightnesses than those with shorter periods. This relation, known as the period-luminosity relation, is used in many cases to calculate distances to stars and galaxies (see Astronomy (Measuring distances in space) ).
Leavitt was born in Lancaster, Massachusetts. In 1892, she received a bachelor’s degree from the Society for the Collegiate Instruction of Women (now Radcliffe College). She joined the Harvard College Observatory in 1902 and spent her entire career there.
