Pickering's Harem
Today honoring a special group of women scientists.
The University of Houston’s College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.
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Every day, most of us use our phones to do a quick calculation. We barely think about it. But imagine a time when even simple math took some mental effort.
A huge burden was removed from astronomy students by 1972. The pocket calculator had suddenly become a common tool. Before that we did so without such electronic aid by hand or with mechanical calculators. So let us visit the Harvard College observatory in the early Twentieth Century.
Its director, Edward Pickering, faced a problem: he needed people who could do all this math. So, he did something unusual for that time — he hired women to help. They were called the Harvard Computers, but nicknamed “Pickering’s Harem.” Back then, it surprised many people to see women doing serious science work.
Edward Charles Pickering (1846 - 1919), Director of the Harvard College Observatory from 1877 until his death. A well-known solar astronomer and promoter of the use of photography in astronomy, his brother, William Henry Pickering (1858 - 1938) was also an astronomer of some note. The older brother is one of the first astronomers to see the value in international groups working together in, for example, the study of variable stars, which change their brightness for a variety of different reasons over time. (Public domain)
These women weren’t trained astronomers, but they were smart, precise, and determined. Their discoveries changed how scientists saw the universe.
Taken in 1890, this group of Harvard Computers includes Henrietta Swan Leavitt (third from left with magnifying glass) and Annie Jump Cannon (in the center foreground, also with a magnifying glass). The graph on the wall with the sinusoidal curve just behind Leavitt’s head is the changing light output of the double (i.e., binary) star system β Aurigae for December 1889. Also known as Menkalinan, it’s the second-brightest star in Auriga, the Charioteer, easily seen high overhead on cold winter nights. (Public domain)
One of them, Annie Jump Cannon, studied the light from stars. When starlight passes through a prism, it makes a pattern called a spectrum. By comparing thousands of these spectra, Cannon grouped stars by their color and temperature. Her system of classifying was so good that astronomers still use it today.
Pickering and the Harvard Computers, 13 May 1913, standing in front of Harvard College Observatory’s Building C, then the newest at the facility. Beginning with the back row, they are (L to R): Margaret Harwood (far left), Mollie O'Reilly, Edward C. Pickering, Edith Gill, Annie Jump Cannon, Evelyn Leland (behind Cannon), Florence Cushman, Marion Whyte (behind Cushman), Grace Brooks. Front row: Arville Walker, unknown (possibly Johanna Mackie), Alta Carpenter, Mabel Gill, Ida Woods. Henrietta Swan Leavitt, though employed by the HCO at the time, is not among them. This photograph of the group was originally found in a photo album belonging to Cannon. (Public domain)
Another Harvard Computer, Henrietta Swan Leavitt, studied stars that pulsed — they got brighter and dimmer in regular cycles. She noticed an important pattern: the slower a star’s pulse, the brighter that star really was. These stars were called Cepheid variables, after the constellation Cepheus.
Another May 1913 photo showing Annie Jump Cannon (1863 – 1941) standing (at left) alongside Henrietta Swan Leavitt (1868 - 1921). This has to have been taken on a different date in front of Building C (based on the ivy on the walls by the door) than the previous picture showing Pickering and the Harvard Computers. Here, Cannon is wearing a different dress. Remarkably, both women suffered with illness-related hearing loss over their careers. (Public domain)
Leavitt’s discovery became a new tool for measuring distances in space. If astronomers knew how long a Cepheid took to pulse and how bright it looked from Earth, they could figure out how far away it was. This let astronomers measure distances across tens of millions of light-years — farther than ever before.
After Leavitt died, Edwin Hubble used her method to study a Cepheid in the Andromeda “nebula.” His results showed that Andromeda wasn’t just a giant cloud of gas inside our galaxy — it was another whole galaxy made up of billions of stars. Thanks to Leavitt’s work, we learned that the universe is far larger than anyone had imagined.
This photographic glass plate negative was made by Edwin Powell Hubble (1889 - 1953) using the world’s largest optical instrument at the time: the 100-inch Hooker Telescope on Mount Wilson. A discovery image, it shows the star-rich central region — the black blob — of the Andromeda Nebula (a.k.a. M 31) as well as certain stars within it. Those marked with an “N” are novae: a short-lived, violent explosion between a white dwarf star orbiting a regular one. The star at the top right between the two hash marks, “VAR!,” is a Cepheid variable. This latter object could be used to make Hubble’s first calculation of its distance, proving this was a completely separate system of billions of stars, now known as the Andromeda Galaxy, outside of our own Milky Way. (Public domain)
Even though the Harvard Computers made huge contributions, they still faced barriers. They weren't allowed to use telescopes themselves — only the photographs made through them by others. Still, their dedication reshaped astronomy and opened doors for future women scientists.
The Harvard Computers remind us of something important: progress doesn’t always hinge on fancy tools. It depends on creative minds using what they have to explore the unknown.
I’m Tom Callen on behalf of the University of Houston, and also interested in the way inventive minds work.
(Theme music)
Some references
Henrietta Swan Levitt - Wikipedia
Edwin Powell Hubble - Wikipedia
For some other aspects of Pickering’s work with the Harvard Calculators, see “The Harvard Computers,” by Andrew Boyd.
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This Episode first aired on 02/03/2026.