Biography 3

Henrietta Leavitt 

Henrietta Leavitt was born in Lancaster, Massachusetts on 4 July, 1868. She was one of seven children born to George Roswell Leavitt, a prominent Congregationalist minister, and Henrietta Swan Kendrick Leavitt. Both being colonials, her parents were extremely strict, and held to the stern virtues of their Puritan ancestors.

Leavitt found her first real opportunity to study astronomy during her senior year at Oberlin College and the Society for Collegiate Instruction of Women, or what is now known as Radcliffe College, from whom she received an A.B. in 1892. She spent an additional year as an advanced student in astronomy, but returned home for several years when she suffered from an illness that left her severely deaf. However in 1895 she became a volunteer research assistant at the Harvard College Observatory. By 1902, after receiving a permanent position there, she had rapidly advanced from a meager assistant measuring the brightness of variable stars, to chief of the photographic photometry department.

This how it happened. A man by the name of Charles Pickering, the director at Harvard during the 1880’s and 1890’s, had embarked on an extensive program to determine what the visual stellar magnitudes were. In 1907, after realizing the importance of photographic magnitudes, Pickering announced his plans to establish a standard photographic sequence that was based on stars near the north celestial pole. Henrietta was able to carry out the plan with “originality, skill and patience”, comparing 299 plates from thirteen telescopes to determine a standard range of brightness of six million. Consequently, this “north polar” sequence was published in the Annals of Harvard College Observatory, providing the standards for most statistical investigations of the Milky Way system until about 1940; Leavitt was appointed to the permanent staff, at a salary of 30 cents an hour, by Charles Pickering.

Leavitt’s most famous discovery, however, was the period-luminosity relation of the Cepheid variable stars, better known as the cepheid variable period-luminosity relationship, originating in her study of variables in the Magellanic Clouds. In 1912 she found that the apparent magnitude decreased linearly with the logarithm of the period. This relation was seized upon by Shapley at the Mount Wilson Observatory, who calibrated the absolute magnitudes of the Cepheid variables, thereby making it a universal tool for ascertaining the size of the Milky Way galaxy and its distance to other galaxies. Basically, what she discovered was a direct correlation between the time it took a star to go from bright, to dim, to how bright it actually was. Knowing this relationship helped other astronomers, such as Edwin Hubble, make their own groundbreaking discoveries. To Miss Leavitt’s contemporaries, however, her more obvious contribution was her discovery of 2,400 variable stars, about half of those being known at the time.

Unfortunately, Henrietta was not allowed to pursue her own topics of study, but instead researched what the head of the observatory assigned to her. Due to the prejudices of the day, she didn't have the opportunity to use her intellect to the fullest. However, Dorrit Hoffleit wrote that although Leavitt was not awarded the honors and publicity of her colleagues, she was just as deserving. “Her most important work required greater understanding and even more meticulous care, and was more desperately needed by other astronomers of the time, even though it lacked the glamour and popular appeal of the newly opened field of stellar spectroscopy.”

Just as her parents raised her, she remained deeply conscientious and religious, devoted to her work and as well as her family. She shared her mother’s home in Cambridge after her father’s death in 1911, working at the Harvard College Observatory until her death from cancer in 1921.