If you've been following Astronomical Returns, by now you know my dual passions in life are space and finance; as a kid, my space obsession manifested itself in countless childhood drawings of rockets and planets. And as for my early interest in all things business and money, I had a knack for coin collecting - I recall eagerly accumulating all 50 state quarters that were issued from 1999-2008, finding the last coin (Hawaii) just as I entered middle school! I haven't been nearly as diligent since then, but two of my favorites I've gotten more recently are the US Mint's 2009 New Frontier Congressional Gold Medal featuring John Glenn and the Apollo 11 crew, and the 2019 Apollo 11 50th Anniversary Commemorative Coin (both gifts from my parents, thanks Mom and Dad!)

This past week, a Facebook ad from the US Mint popped up in my newsfeed showcasing their new American Innovation $1 coin series. To be minted between now and 2032, each coin celebrates an invention or pioneer from each of the 50 states + the various territories. As the first state to ratify the Constitution, Delaware was first to release its American Innovations coin, and they chose to honor Annie Jump Cannon, the legendary Delaware-born astronomer who in the early 1900s invented a stellar classification system still used today! The coin features her silhouette against a night sky with the words "Classifying the Stars". Great choice Delaware, I tip my hat to you! This Texan eagerly awaits finding out who or what his home state will feature when Texas releases its coin in 2025

Annie Jump Cannon was born in 1863 in Dover, Delaware. At a young age, her mother inspired her passion for astronomy, as the two of them would frequently observe the night sky through the trapdoor of the roof in the small observatory they built together. She encouraged Annie to pursue physics and astronomy at Wellesley College despite the fact women rarely pursued STEM fields at the time. After graduating as valedictorian, she spent several years taking graduate courses and traveling through Europe learning the new art of photography before joining the Harvard Computers in 1896. This all-female cohort worked for Edward Pickering at the Harvard Observatory, whose goal was to map every star in the night sky down to a photographic magnitude of 9 (about 16x fainter than the human eye can see) as part of the massive Henry Draper Catalogue, decades in the making 

Here's the task that Pickering and the Harvard Computers were faced with: for decades, astronomers had known that stars could be characterized by their optical spectra, the bands of light at specific wavelengths every star absorbs from the visible light spectrum, depending on its unique chemical composition. Before, astronomers had to pass the light from each star they observed through a prism in their telescope, then manually draw the absorption lines for later classification. But by the time of Cannon and the Harvard Computers, photographic plates had been invented, significantly speeding up the process and producing an enormous data set that needed a system of organization

Simple diagram of how a spectroscope identifies stellar composition, comparing absorption lines to known emission wavelengths of various elements

 

There was initially disagreement on what the best classification method was - fellow computers Williamina Fleming and Antonia Maury had devised more complex systems with 15 and 22 different categories, respectively. Instead, Cannon crafted a much simpler classification that still drew on Fleming and Maury's emphasis on hydrogen and helium but narrowed it down to 7 groupings. Each star got a letter designation based on its spectral class: O, B, A, F, G, K, M (always taught with the mnemonic "Oh Be A Fine Girl, Kiss Me"), and with her efficient methodology, Cannon began sifting through mountains of absorption spectra data and classifying stars at breakneck speeds of 200 assignments per hour! 

Despite the gender inequality of the time - only the male astronomers operated the telescopes, while the women were given the task of analyzing the data for a measly salary of 50 cents an hour - the Harvard Computers quickly gained popularity among their male counterparts for their spectacular accuracy, speed, and patience with the tedious work of classifying stars. And although a bout of scarlet fever had almost completely robbed Cannon of her hearing a few years prior, she excelled in her task so much that Pickering himself said, "Miss Cannon is the only person, man or woman, who can do this work so quickly." By 1901, Cannon had published her first stellar catalog, and in the subsequent decades she drew international fame, becoming Curator of Astronomical Photographs at Harvard, an honorary member of the Royal Astronomical Society, and receiving an honorary doctorate from Oxford University

The famous Hertzsprung-Russell diagram, with Cannon's spectral classifications at the top

By the time Cannon died in 1941, she had manually classified a mind-boggling 350,000 stars in her lifetime, far more than anyone else. And beyond her pioneering work in astronomy, Cannon was a fierce advocate for women in science and for women's suffrage

To learn more about the amazing life of Annie Jump Cannon, I recommend this great Forbes article!