11th December, 2018 marks the 155th birth anniversary of Annie Jump Cannon, a deaf woman who changed the face of astronomy. Cannon, along with Pickering, is credited with developing a system of classification of stars, now known as the Harvard system. This was the first serious attempt to classify trillions of star in the universe. From learning about constellations in her mother’s lap to catagorizing the stars, Cannon’s story is an inspiring one.
Cannon was born in Delaware, US. Her mother was the first person to introduce her to astronomy. She always advised her to follow her heart, no matter what. Cannon’s mother taught her about the constellations and seeing her interest in astronomy, she advised her to study Mathematics, chemistry and biology. Cannon took her mother’s advice and pursued her love of astronomy. Cannon suffered hearing loss sometime during her childhood or early adult years. Her hearing loss made it difficult for her to socialize, resulting in her immersing herself in her work. She never married and did not have children.
In 1880, Cannon was sent to Wellesley Collegein Massachusetts, one of the top academic schools for women in the US, where she studied physics and astronomy. In order to gain access to a better telescope, Cannon enrolled at Radcliffe College as a “special student”, continuing her studies of astronomy. Radcliffe was set up near Harvard College for Harvard professors to repeat their lectures to the young Radcliffe women. This relationship gave Cannon access to the Harvard College Observatory.
In 1896, She became a part of “Pickering’s Women”, a group of women hired by the director of Harvard Observatory in order to complete the Henry Draper Catalogue that aimed to map every star in the universe up to a visual magnitude of 9. Soon, a disagreement started developing among the women as to how to classify the stars? Every woman had a different idea.
Cannon negotiated a compromise: she started by examining the bright southern hemisphere stars to which she applied her own system of classification. She studied the spectrum of every star and classified them into 7 categories: O,B,A,F,G,K and M type stars. This classification was based on the relative strength of the Balmer series absorption line. After absorption lines were understood in terms of stellar temperatures, her initial classification system was rearranged to avoid having to update star catalogs. Astronomy students are taught to use a mnemonic of “Oh Be a Fine Girl, Kiss Me” as a way to remember stellar classification.
Cannon manually classified more stars in a lifetime than anyone else, with a total of around 350,000 stars. She discovered 300 variable stars, five novas, and one spectroscopic binary, creating a bibliography that included about 200,000 references. She discovered her first star in 1898, though she was not able to confirm it until 1905. When she first started cataloging the stars, she was able to classify 1,000 stars in three years, but by 1913, she was able to work on 200 stars an hour. Cannon could classify three stars a minute just by looking at their spectral patterns and, if using a magnifying glass, could classify stars down to the ninth magnitude, around 16 times fainter than the human eye can see. Her work was also highly accurate.
Annie Jump Cannon’s career in astronomy lasted for more than 40 years, until her retirement in 1940. Despite her retirement, she continued to actively work on astronomy in the observatory up until a few weeks before she died. Cannon died on April 13, 1941, in Cambridge, Massachusetts, at the age of 77. She died in the hospital after being ill for over a month.
Cannon’s life and career is an inspiration that one should always follow one’s heart and work day and night to achieve something in life. Sad that such a noble discovery wasn’t even considered once for the Nobel Prize. Today, a significant part of stellar astrophysics rests on her discoveries.