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Annie Cannon: The Woman Who Classified Stars

silhouette of telescope against starry night sky
Vadim Sadovski/Shutterstock

Annie Jump Cannon was one of the most important scientists you’ve probably never heard of. Her work as an astronomer, suffragist, and activist broke new ground for women. In particular, her dedication to astronomy resulted in a major classification system that’s still used today.

Early Start in Astronomy

Cannon studied the stars for almost her entire life. Mary Jump, Annie’s mother, encouraged her daughter to pursue her passion for them from a young age. In fact, Mary was the first person to teach Annie how to locate and identify the constellations. According to an archival biographical overview from Berkeley, Mary was an amateur astronomer who passed on her love of stars to her daughter: “Using an old astronomy textbook as a guide, mother and daughter would peer out of their attic at the night sky and try to identify as many stars as they could.”

In 1880, Cannon began attending Wellesley College, one of the oldest American universities for women. There, she studied astronomy and physics, eventually graduating as valedictorian of her class. Wellesley’s biography of Cannon notes that she technically graduated with a degree in physics since the school didn’t offer a degree in astronomy at the time. Nevertheless, Annie went on to pursue her interest in astronomy, focusing mainly on spectroscopy, which involves investigating and measuring the frequency of the wavelengths produced when matter interacts with or emits electromagnetic radiation.

According to the San Diego Supercomputer Center, Cannon’s career took a slight detour when her beloved mother died—until after 1894, that is. At this point, she wrote to Sarah Frances Whiting, one of the only female physicists in the U.S. back then and one of her former professors from Wellesley. Whiting hired Canon for a junior teaching position in the physics department, an opportunity which gave her the chance to take graduate-level courses while there. She also became a “special student” at Radcliffe College—the women’s sister school to Harvard—and gained access to the Harvard observatory.

Classification System

In 1896, Cannon joined the Harvard Computers, a group of women that Harvard College Observatory director Edward C. Pickering had hired for a project known as the Henry Draper Catalogue. Named after an amateur astronomer whose widow had set up a fund to support astronomy research, the project’s goal was to measure the spectra of as many stars as possible, then index and classify them based on those measurements.

Two other women had already developed classification systems for Pickering’s project, as SDSC explains. First, Williamina Fleming developed a 22-class system based on her observations of over 10,000 stars. Then, after Fleming, Antonia Maury took up the reins and developed her own system with a more theoretical framework underlying the classification system, which made it more complex and frequently frustrated Pickering.

Finally, it was Cannon’s turn. For her system, she proposed using spectra characteristics as the foundation of a classification system. She assigned each class a letter: O, B, A, F, G, K, and M. Over the course of her career, she classified more stars than anyone else—over 350,000, along with over 300 stars she personally discovered. Over time, she developed a reputation for remarkable speed and accuracy in classifying stars. She could classify up to 200 stars per hour at her peak.

Ongoing Legacy

Although the field of astronomy has shifted over the years, Canon’s star classification system remains largely intact. It was originally based on something called Balmer absorption lines. However, once these lines were understood to be related to temperatures, the classification—now commonly known as the “Harvard Classification System”—was merely reordered.

Cannon’s work was slowly recognized over the course of her life. In fact, she gained a fair number of “firsts” for women in astronomy. In 1911, she was appointed the Curator of Astronomical Photographs at Harvard. Three years later, she became the first woman to be admitted as an honorary member of the Royal Astronomical Society. In 1925, she was the first woman to receive an honorary doctorate of science from Oxford. Her publications continued throughout her life, although interestingly, it took her longer to get a full-fledged position at Harvard than it did to cross any of these milestones. It wasn’t until two years before her retirement in 1938 that she was finally given a proper appointment as the William C. Bond Astronomer at Harvard.

Canon continued working until her death in 1941. Her legacy lives on in today’s astronomy classrooms. Every year, the American Astronomical Society presents an award in her name to women who distinguish themselves in the field. This is a fitting way to further the name of a scientist who not only broke a glass ceiling for women, but also for the entire world of astronomy in general.

Amanda Prahl Amanda Prahl
Amanda Prahl is a freelance contributor to MindBounce. She has an MFA in dramatic writing, a BA in literature, and is a former faculty associate focusing on writing craft and history. Over the past several years, she's researched and authored a wide range of articles centered on the arts, humanities, history, and pop culture. Read Full Bio »