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  • Writer's pictureDale DeBakcsy

She Filled the Sky: Annie Jump Cannon, Iron Woman of Astronomy.

350,000 stars classified.

It's one of astronomy’s unbreakable and frankly not even approachable records, the scientific equivalent of the Ripken Streak. Seven hours a day, six days a week, for forty-four years, one woman bent herself to the task of creating an ultimate chart of the night sky, with each star classified not only by position, but by surface temperature and spectral signature. Hunched over a magnifying glass, she could categorise three stars a minute where others might take three minutes to categorise one star. She was astronomy’s Iron Woman – Annie Jump Cannon.

For the first thirty-three years of her life, Cannon shared the fate of most highly educated and intelligent Nineteenth Century American women – a drifting existence desperately lacking purpose. Her mother had raised her with a passion for the stars. The two climbed the attic ladder nightly to look up at the sky and identify the constellations there. She went to Wellesley College and, in spite of an illness that caused substantial hearing loss, she graduated valedictorian in 1884. She was smart, young, and passionate about science and, as far as society was concerned, she was done. She drifted for the next nine years, traveling the world, taking pictures with her beloved Kamaret, writing articles about the places she’d visited, and always haunted by the knowledge that, with her intellectual gifts, she could be so much more. She poured her frustration into her diary:

‘I am sometimes very dissatisfied with my life here. I do want to accomplish something, so badly. There are so many things that I could do if I only had the money. And when I think that I might be teaching and making money, and still all the time improving myself, it makes me feel unhappy and as if I were not doing all that I can.’

When her mother died in 1893, Cannon took it as a sign to do something with her life. She got a job teaching at Wellesley and began graduate studies at Radcliffe, an institution with ties to the Harvard Observatory. Cannon became one of Pickering’s computers, and her work lay in steady exactitude, which she managed by refining the classification system she inherited from Fleming into the system that all astronomers everywhere now use to quickly categorise and rank stars by. Synthesizing the various over-complicated systems of her day, she created the OBAFGKM scale of stellar intensity and its subcategories (O stars are the hottest, M the coolest), which for many years taught to male undergraduates with the not entirely enlightened mnemonic Oh Be A Fine Girl Kiss Me.

Tasked with the massive, seemingly impossible, task of classifying all the stars in the sky down to magnitude 9 (sixteen times dimmer than the unaided human eye can see) according to her system, in her forty four years at Harvard she not only catalogued to magnitude nine, but to magnitude eleven, amassing in the process 350,000 stars in an era before computerised stellar recognition was even a wisp of a dream. By visual inspection, she had to interpret the achingly faint smear of a star’s spectrum that had been produced by telescopes equipped with a spectroscopic wedge. It took keenness of eye married to a total familiarity with spectral astronomy and stellar composition to even begin to make sense of those smudges, let alone to process them definitively at the break-neck pace of three a minute.

Her work was so universally respected by the astronomical community that she was able to use her success to open the door to other female astronomers, endowing the Annie J Cannon Scholarship for women entering the field. She was made curator of astronomical photographs in 1911, but was refused a professorship on account of her gender. Likewise, she was nominated for the National Academy of Sciences, but was curiously rejected on account of her deafness.

I'm not sure how that works either.

After forty-four years of unfathomably steady work and dedication, Cannon retired in 1940 at the age of 77, and inevitably continued working anyway. She was a dedicated suffragist, and a tireless proponent of women in science, always willing to donate time and hard-won money to promote women of talent. Her work ethic was unparalleled, but all who knew her remembered her most for her kindness, for turning the drudgery of astronomical sifting into a personal adventure. Cecilia Payne-Gaposchkin captured that essence when she said, ‘To [her friends] she was not the great scientist... she was a human being, and as such they loved her – they, and their children and their grandchildren. Perhaps the greatest tribute that I can pay to her memory is to say that she was the happiest person I have ever known.’

Annie Jump Cannon died in 1941. The lunar crater Cannon is named in her honour.


In the Footsteps of Columbus is a curious book that Cannon wrote before becoming an astronomer, a collection of photographs and essays taken and written during a trip to Spain. It's an interesting document about the dawn of amateur photography, but more importantly, in the edition annotated by Doug West, there is the only substantial stand alone biography of Cannon we have appended at the end. Apart from that, you have to make due with guest appearances in other books – George Johnson’s excellent Miss Leavitt’s Stars and Dava Sobel’s equally wonderful The Glass Universe.

And if you'd like to read more about women astronomers like Jill Tarter, check out my History of Women in Astronomy and Space Exploration, which you can order from Amazon, or from Pen and Sword US or UK.


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