When Edward Pickering was appointed Director of the Harvard Observatory in 1877, it was a big surprise to many in the astronomical community because he had no track record for shucking on lots of clothes and working through the chilly night peering at stars through a telescope. That was the way progress had always been made in astronomy ever since the famous claim that Galileo had observed planets orbiting round Jupiter. One of the issues with this model was that in the northern temperate zone, where all the money to sponsor telescopes was, the night-time weather was somewhere between reliably unreliable to unrelievedly awful. It is no coincidence that the Babylonians lived in a region where the nocturnal optics were clear enough to obtain data on successive nights. What Pickering brought to the table was a table
: in a warm dry well lit room where he could study photographs of the sky obtained under less salubrious conditions the previous night. He was by no means the first person to make use of stellar photography, indeed when he took up the directorship there were stacks of under-analysed data in the form of glass photographic plates.
He set out to classify the stars according to their location and magnitude (brightness) and invented a meridian photometer which used a prism to directly compare the brightness of a star down near the horizon with Polaris which was known to have a reliable magnitude. There are a helluva lot of stars out there when you start pointing telescopes at them. With the unaided eye, the number is a much more comfortable 6-10,000 stars with are brighter than Mag.6. This is usually taken as the limit of 'normal' human vision. Stellar magnitude goes the 'wrong way', such that higher magnitude means dimmer and the very brightest stars (Sirius, Canopus, Alpha Centauri, Arcturus) therefore require negative magnitude. It is comparatively easy to look at a star or photograph it or measure its spectral properties but it takes time. Clearly the bottleneck is at the telescope, so you don't want to have an astronomer peering up at the sky through an expensive piece of kit and a gap in the clouds making little drawings and taking notes with a pencil seized in his gloved hand.
Pickering left all the primary data gathering to other people, and taking the photographs increasingly became mechanised and carried out by robots. Instead, he hired lots of young men with steady hands and good eyes to analyse the photographic plates. It was about 100 years before machines could equal the human eye for discriminatory precision. One day he looked over the results that his minions had generated and tore strips off them for their poor quality and lack of attention to detail, famously uttering the jibe "Why, my Scotch maid could do better".
The Scotch maid was Williamina "Mina" Fleming
(L) from Dundee, a single mum who left school at the age of 14. She was working in Pickering's home as a maid after her husband abandoned her in Boston while she was pregnant. It turned out that Fleming was indeed better than the idle young male wannabe astronomers and she was happy to carry out the tiresome drudgery of looking at plate after plate and cataloging the contents. Thereafter Pickering hired and Fleming trained dozens of initially young women to crank through the backlog of plate-data. These were compiled into the Henry Draper Catalog of stars which was published in the 1920s and eventually included 360,000 stars and other astronomical objects. Henry Draper was the first person to capture the spectrum of a star (Vega, Mag 0.3, as it happens) on a photographic plate. It was his widow who bankrolled Pickering's project as a memorial to her late husband. Fleming classified the stars according to their hydrogen
content giving similar stars the same letter code. One of the Pickering-Fleming trainees, the wonderfully named Annie Jump Cannon, later reclassified everything on the basis of temperature, which is the classification we use today. Mina Fleming is now known to have discovered of the iconic star-gazers poster, the horsehead nebula, shown at the head of this post. At the time this was credited to William Pickering, Edward's younger bother (and a respected astronomer in his own right), who took the photograph. A significant part of the task carried out in the Harvard laboratory was mathematical calculation and the women who carried out the work were known as 'computers'. When electronic computers were invented two generations later, the name was there for the taking. In 1906 she was made an honorary member of the Royal Astronomical Society following an ancient tradition by following star star-gazers Caroline Herschel and Mary Somerville into that halfway, not proper fellows, position. In fairness, the RAS was a generation or two ahead of other institutions in according women full fellowship in 1916.
Other women in science on The Blob
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