When it comes to prestige in US education, few names carry more weight than Harvard University.
Founded in 1636 in Cambridge, in the Massachusetts Bay Colony, as New College, Harvard is the US’s oldest institution of higher education.
People today might think of Harvard for its legal and business studies but from its early days it was known as a centre of scientific research.
Less known is the role that women played at Harvard in developing astronomy as a science. Prominent among these starry women was Henrietta Swan Leavitt, born on 4 July 1868 in Lancaster, Massachusetts.
In 1888 Leavitt entered the Society for the Collegiate Instruction of Women, which later became Radcliffe College, an offshoot of male-only Harvard. Her studies ranged from classical Greek, fine arts and philosophy, to analytical geometry and differential calculus.
Let’s backtrack a little to set the scene.
In 1839, William Cranch Bond was persuaded to bring his own equipment to Harvard to establish a de facto observatory and to serve as the college’s first (unpaid) “Astronomical Observer”.
“A visit from a brilliant comet a few years [in 1843] later helped stimulate the purchase of a 15-inch [38 cm] Great Refractor telescope from Munich, which remained the largest instrument in America for the next two decades,” Harvard’s official history says.
In 1877, Harvard graduate Edward Charles Pickering left the Massachusetts Institute of Technology (MIT), where he was a professor of physics, to become professor of astronomy and director of the Harvard College Observatory.
Smithsonian Magazine’s 2013 article “The women who mapped the Universe and still couldn’t get any respect”, called Pickering a “progressive thinker – at least when it came to opening up educational opportunities”.
It says that while at MIT Pickering “revolutionised” scientific education “by encouraging students to participate in experiments”. He was also noteworthy for inviting female students to attend his lectures.
One of Pickering’s most important innovations at Harvard Observatory was to take advantage of recent developments in astrophotography taken by attaching cameras to telescopes. He introduced the use of the meridian photometer to measure the magnitude of stars and established a catalogue of photographs.
So enthusiastic was Pickering for this new field of discovery that the number of images produced overwhelmed his staff’s ability to analyse them.
“So began an era in Harvard Observatory history where women – more than 80 during Pickering’s tenure, from 1877 to his death in 1919 – worked for the director, computing and cataloguing data,” Smithsonian says.
Viewed one way, this could be seen as an advancement for women in science, or at the very least in the workforce.
Referred to as “computers”, women working at the observatory studied and curated glass-plate photographs that became known as the HCO Astronomical Photographic Plate Collection, which the university says is “the world’s largest archive of stellar glass plate negatives, amassing over 500,000 celestial moments captured in time, some dating back to the mid-1800s”.
“Some of these women would produce significant work on their own; some would even earn a certain level of fame among followers of female scientists,” Smithsonian says. “But the majority are remembered not individually but collectively, by the moniker Pickering’s Harem.”
Even after Pickering’s death, women performed largely clerical tasks such as reducing photographs to render images as clear as possible; classifying stars by comparing photographs to known catalogues; and cataloguing the photographs themselves, making careful notes of each image’s date of exposure and the region of the sky. Notes were then copied into tables, which included the star’s location in the sky and its magnitude.
In 1912, “computer” Henrietta Swan Leavitt made a discovery that the American Association of Variable Star Observers (AAVSO) says “was to become one of the cornerstones of modern astronomical science”.
Leavitt’s work had involved examining images of Cepheid variables, which the CSIRO describes as “types of pulsating variable stars [that] exhibit a definite relationship between their period and their intrinsic luminosity. Such period-luminosity relationships are invaluable to astronomers as they are a vital method in calculating distances within and beyond our galaxy.”
But the real discovery was yet to come. “While recording and cataloguing the data on her variable stars, Leavitt found she could accurately and consistently relate the period of a given star’s brightness cycle to its absolute magnitude,” says the AAVSO. “The discovery of this simple and hitherto-unknown relationship made it possible, for the first time, to calculate their distance from Earth.”
In 1908 Leavitt published a paper called “1777 variables in the Magellanic Clouds” in the Annals of the Astronomical Observatory of Harvard College. In it, she noted that the brighter variables had the longer period.
In 1912, in the Harvard College Observatory Circular, she published “Periods of 25 variable stars in the Small Magellanic Cloud”.
The CSIRO notes that Leavitt received scant recognition for her work but later astronomers such as Edwin Hubble and Ejnar Hertzsprung used her discoveries as foundations on which to build their own research.
In 1924, Hubble was able to use the Cepheid variables to calculate the nebula Andromeda’s distance from Earth, which was the first measurement for a galaxy outside the Milky Way.
The AAVSO says that in 1925, Swedish mathematician Gosta Mittag-Leffler wrote a letter to Leavitt in which he signalled his intention to nominate her for the Nobel Prize in Physics.
He was told that Leavitt had died, of stomach cancer, on 12 December 1921.