Unsung Heroes: Annie Jump Cannon

How many stars are there in the sky? If you’re the fantastically named Annie Jump Cannon the answer is “at least 230,000”. Working at Harvard Observatory around the end of the 19th century, Cannon is credited with pioneering the first organised system of classifying stellar objects, the Harvard Classification System. Nicknamed “The Census Taker of the Sky”, she classified almost a quarter of a million stars, more than anyone else has ever done – including 300 she personally discovered.

Possessing a sharp mind, and with the good fortune of coming from a family that could afford quality education, Cannon had attended Wellesley College and graduated with a degree in physics in 1884. Finding the limited career options of home life boring, and having little in common with her peers, being (paraphrasing from her autobiographical writings) older and better educated, Cannon returned to Wellesley in 1894. Guided by her former instructor, the formidably minded professor Sarah Frances Whiting, Cannon took graduate courses in astronomy and spectroscopy (a relatively new development in imaging at the time), and discovered her true calling.

After two years of graduate study, and looking to get access to Harvard’s superior telescope facilities, Cannon was hired at the Harvard Observatory as part of the group that would become known as “Pickering’s women”. The Harvard Computers, to use the group’s actual name, were a small group of women hired by Edward Pickering to work through the raw data being gathered by the observatory (this of course being a time when a computer was still generally a person who calculated things, not a machine). Pickering had hired Cannon and her fellow computers largely because women were cheaper to employ than men, allowing him to hire more of them; a neccessity given that the rate at which data was being gathered was outstripping the rate at which it could be processed.

So, what was Cannon earning, given her degree and graduate work at one of America’s most prestigious private colleges, and the fund set up by the wealthy physician Anna Draper to support the observatory’s work? Somewhere in the region of $0.25 to $0.50 an hour. This put her slightly above an unskilled factory worker, and somewhat below a clerical or secretarial worker. What would a lot of us do in the face of woefully poor pay despite excellent qualifications and a natural talent? Probably look for new work, or failing that become disillusioned and start putting in less effort than perhaps we should.

Fortunately for modern astronomers, Annie Jump Cannon had a passion for her field, a drive for progress, and a rather brilliant mind for organising and classifying abstract data. Rather than throw up her arms in frustration at the poor pay and oten tedious work of examining stellar images she set herself to the task of examining the bright stars of the Southern hemisphere.

Now for some vaguely sciencey details: at the time, there was a disagreement between two others working at the observatory, Antonia Maury and Williamina Fleming, as to how stars should be classified. Cannon pioneered a third system, classifying stars based on the strength of their Balmer absorption lines (one of a set of series that describe the spectral line emissions of hydrogen atoms, the strength of a star’s Balmer absorption lines provide a reliable indicator of the stars temperature). This provided a thorough and yet elegant means of classifying stellar objects, dividing them into letter categories based on temperature. When astronomers refer to our sun as a G-type star, that’s Cannon’s classification system in action.¹

Following her groundbreaking work on stellar classifications, Cannon remained dedicated to the field of astronomy, eventually receiving a regular appointment at Harvard as the William C Bond Astronomer, in addition to receiving an honorary doctorate from Oxford (the first one given out to a female academic). Her legacy lives on for astronomers, both in the ongoing use of her work and in the Annie Jump Cannon Award, given out by the American Astronomical Society to pioneering female researchers in the field. Even off the planet, Cannon’s memory lives on, one of the Moon’s craters being named in her honour.

So, next time you’re looking up at the sky, keep in mind Annie Jump Cannon, who more than likely labelled most of the stars you can see.

(As a final note, Cannon was not the only woman working in the Harvard Observatory at the time to do amazing things. Henrietta Swan Leavitt‘s work on Cepheid stars arguably provided the vital theoretical underpinnings on which much of Edwin Hubble’s work was based. She received almost no recognition for her discoveries during her own lifetime.)

• Unsung Heroes: spotlighting fascinating people we never learned about at school. Rob Mulligan also blogs at Stuttering Demagogue. Stay tuned for future Heroes, or send your own in to [email protected]!

1. For the curious, the stars are classified from hottest to coldest as O, B, A, F, G, K and M. The hotter stars tend to be more massive and less common than their colder cousins. The classes are further sub-divided into 0-9, 0 being the hottest in a class and 9 the coldest. Our own sun is a G2 star. [↩]