Henrietta Swan Leavitt was an American astronomer born on July 4, 1868. She worked at the Harvard College Observatory and made significant contributions to the field of astronomy, particularly in the study of variable stars. Her most notable achievement was discovering the relationship between the brightness and the period of Cepheid variable stars, which later became crucial for measuring cosmic distances. Leavitt's work laid the foundation for the development of the cosmic distance ladder, allowing astronomers to determine how far away galaxies are from Earth. Despite her groundbreaking discoveries, she faced challenges as a woman in science during the early 20th century, often receiving little recognition during her lifetime.