Complex sentence: Henrietta Swan Leavitt (July 4,1868--December 12,1921) was an American astronomer who discovered the relation between the luminosity and the period of Cepheid variable stars.
Split into simpler sentences: Henrietta Swan Leavitt (July 4,1868--December 12,1921) was an American astronomer. Leavitt discovered the relation between the luminosity and the period of Cepheid variable stars.