Every astronomer alive sorts stars using a system worked out by a shipbuilder's daughter from Dover.
The sequence is O, B, A, F, G, K, M. It runs from the hottest stars to the coolest, it is taught in every introductory astronomy course on earth, and generations of students have memorised it with the mnemonic Oh Be A Fine Girl, Kiss Me — usually without being told that the person who put those letters in that order was a woman from Delaware who was nearly deaf for most of her working life.
Her name was Annie Jump Cannon. She was born in Dover on December 11, 1863, and she classified roughly three hundred and fifty thousand stars by eye — more than any other human being who has ever lived.
The attic
Her father, Wilson Cannon, was a Delaware shipbuilder and a state senator. Her mother taught her the constellations.
The detail that survives from that Dover childhood is a good one: mother and daughter in the attic of the house, working from an old astronomy textbook, identifying stars through the window. It is the kind of small domestic scene that usually gets lost, and it happens to be the origin point of a system now used on every continent.
There is a resonance in the shipbuilding, too, though it should not be pushed further than the record supports. Wilson Cannon built vessels in a state whose entire commercial life ran on the Delaware River and Bay, in a century when getting a ship anywhere still meant knowing the sky. Nobody recorded whether that connection meant anything to his daughter. It is simply true that she grew up in a household where the water mattered and the stars were not decoration.
Wellesley, and a long detour
Cannon went to Wellesley in 1880, studied physics and astronomy under Sarah Frances Whiting, and graduated valedictorian with a physics degree in 1884.
Then, for roughly a decade, not much. She went home to Dover. This was the ordinary fate of an educated American woman in the 1880s: there was very little for her to do with a physics degree, and she did very little with it.
Somewhere in that period she contracted scarlet fever and lost most of her hearing. The sources here are worth flagging rather than smoothing over — accounts vary on both the timing and the precise cause of her deafness, and the commonly repeated version, scarlet fever around 1893, is the standard account rather than a settled one. What is not in question is that she was nearly deaf for the whole of her professional career, which began after it.
The Harvard Computers
In 1896 Edward Pickering hired her at the Harvard College Observatory.
Pickering had assembled a staff of women to process astronomical data — the group history now calls the Harvard Computers, a job title that meant exactly what it says. They examined photographic plates of stellar spectra and recorded what they saw. The pay was low, the work was repetitive, and the labour was very largely invisible in the published science.
The problem Cannon walked into was a mess. Two colleagues had produced competing classification schemes: Antonia Maury's, which was intricate and precise, and Williamina Fleming's, which was simple and fast. Neither had won. The field had a growing pile of spectra and no agreed way to file them.
Cannon's contribution was not to invent a third scheme. It was to reconcile the two — to reorganise the existing letters into a sequence ordered by the strength of the Balmer absorption lines, discard what did not work, and produce something that was both fine-grained enough to be useful and simple enough to actually apply. O, B, A, F, G, K, M, each class subdivided into ten steps.
What she had found, though it was not fully understood as such at the time, was temperature. The sequence runs from the hottest stars to the coolest. A filing system turned out to be a physical ordering of the universe.
Three stars a minute
The volume of her output is genuinely difficult to hold in the mind.
Early on she managed around a thousand stars in three years. By 1913 she was working at roughly two hundred stars an hour — about three a minute, sustained, by eye, from photographic plates. Over her career the total came to something in the region of three hundred and fifty thousand.
The results were published as the Henry Draper Catalogue between 1918 and 1924, across multiple volumes of the Harvard College Observatory annals. It remains one of the foundational reference works of modern astronomy, and it is substantially the work of one woman looking at glass plates.
On May 9, 1922, the International Astronomical Union formally adopted her system. It has not been replaced.
The honours, late
Recognition arrived, slowly, and mostly from outside the United States first.
The University of Groningen gave her an honorary doctorate in 1921. In 1925 Oxford made her the first woman ever to receive an honorary doctorate from that university. In 1931 she became the first woman awarded the Henry Draper Medal by the National Academy of Sciences — a medal named for the catalogue she had largely built.
She worked at Harvard until shortly before her death in 1941.
What Delaware has of her
Delaware's civic memory is heavily weighted toward one week in 1787 and one ride in 1776. Both of those get statues, licence plates and quarters.
Annie Jump Cannon reorganised the sky. Every professional astronomer on the planet still uses her letters, most of them without knowing whose they were, and the sequence began with a girl and her mother in an attic in Dover with a borrowed textbook, looking out of a window.
The First State likes being first at things. This one is genuinely unmatched: no human being has ever classified more stars, and nobody is going to, because the work is done by machines now.
She did it by hand, three a minute, without hearing much of anything.
Sources: Harvard College Observatory and Wolbach Library materials on Annie Jump Cannon and the Harvard Computers; Encyclopaedia Britannica; National Women's History Museum; standard reference accounts of the Henry Draper Catalogue and the 1922 adoption of the Harvard spectral classification by the International Astronomical Union. Sources vary on the timing and cause of Cannon's deafness; the scarlet fever account of about 1893 is the standard version and is described here as such rather than as settled fact. The figure of roughly 350,000 stars is the commonly cited career total and is approximate. No photograph of Cannon is used here because reuse rights for the available portraits were not established; the illustration is the publication's own.