Henrietta Swan Leavitt: Biography, Discoveries & Accomplishments

Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

In the early 1900s, a young woman working in the Harvard Astronomy discovered a way to determine how far away distant stars really were. Her name was Henrietta Swan Leavitt, and in her short life, she was able to make some remarkable astronomical discoveries.

How Far Away is That Star?

How can astronomers tell how far away a star is? It's not as if a person can travel there and measure the distance! Until about one hundred years ago, it was impossible to accurately measure the distance from Earth to distant stars and galaxies. It took a remarkable woman, working with a whole group of other remarkable women, to give us a way to do what seemed to be impossible at the time.

At a time when most women were not expected, or even allowed, to work outside the home, there was a group of remarkable women working at the Harvard Observatory who were quietly helping to revolutionize the world of astronomy. Collectively, they were known as the Harvard computers, and one of their most successful members was a young woman named Henrietta Swan Leavitt who would discover a way to determine how far away distant stars and galaxies really were.

Henrietta Swan Leavitt as work at one of the Harvard computers
Henrietta Swan Leavitt at work in the Harvard Observatory

Early Life and Education

Henrietta Swan was born in 1868 in Massachusetts. Unlike many women in the 1800's, she went to college, attending both Oberlin College and Radcliffe College and graduating from Radcliffe in 1892. In college, she did not focus on astronomy or even science, but instead pursued a broad liberal arts education that included languages, art, and mathematics. Near the end of her college career, she decided to take a course in astronomy, and this decision would change her life. She was captivated by the study of the stars, and decided to sign up for more astronomy courses and pursue an advanced degree in the subject.

Unfortunately, shortly after graduation, Leavitt became very sick, and even after she recovered, her hearing was permanently damaged. She would suffer from health problems for the rest of her life, but she didn't let it keep her down. Even though she was too sick to attend school full-time, she volunteered at the Harvard Observatory from 1893-1895.

Discovery of Leavitt's Rule

While there, she studied a certain type of star called a Cephied variable star that varied in brightness over time. The variation in brightness of these stars follows a regular pattern. Over a period of time, which might be days or weeks or even months, depending on the star, it will be bright, then dim, then reach the maximum brightness again. This pattern repeats over and over, taking the same amount of time for each cycle. The time it takes for this pattern to repeat once is known as the period of the star.

RS Puppis, one of the brightest Cepheid variable stars in our galaxy
Cepheid variable star

By looking at images of a Cephied variable stars over many, many days, Leavitt was able to determine the period of the star. During her time as a volunteer at the observatory, she measured the periods of many Cepheid variable stars and began to see some patterns that no one had noticed before.

In 1896, she left Massachusetts to travel in Europe, and then moved to Wisconsin to live with her father. For several years, she taught classes at Beloit College, but she never forgot about her work at the observatory.

In 1902, Leavitt wrote a letter to the director of the Harvard Observatory, Edward Pickering, and told him that she wanted to get back to work in astronomy. She asked if he knew of any observatories that might hire her that were located in warm climates. Because of her continuing health problems, she wanted to move somewhere warmer than Wisconsin! That was not to be, however. Instead, Pickering invited her to come back to Harvard and join his team of female computers who were all working together in the observatory. At that time, there were about 80 other women working as computers at Harvard!

She agreed, and when she got there, she resumed studying the Cepheid variable stars that she had examined years earlier. It wouldn't be long before she would make a revolutionary breakthrough in our understanding of these stars.

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