How Harvard women cut the keys to the Universe
“I’ll bet you that my HOUSEKEEPER can do a better job!”
This – or something like this – was apparently the line yelled at a male assistant by Edward Pickering, head of the Harvard Observatory, in 1877.
No one knows what blunder sparked the outburst, though we can bet that it was a whopper, given that women weren’t allowed even to operate a telescope at the time.
But we do know that Pickering made good on his bet – first hiring his housekeeper, and then many other women, to measure the brightness of stars – and that winning it would prove to be probably his greatest contribution to science.
Two of “Pickering’s harem” would devise entire new and efficient ways to classify the stars, while a third – Henrietta Leavitt – would do nothing less than revolutionize the way humans measured and understood their universe.
(Edwin Hubble would simply use Leavitt’s ideas and the world’s best telescope to make “the discovery of the century” in the 1920s – that our universe is filled with galaxies like our own, and is expanding.)
Still another woman, Cecilia Payne, would later come to Harvard to join the world’s most female-dominated science lab in the world, and discover for the first time what stars are really made of.
As a Harvard astronomy undergrad, I first heard the story of “Pickering’s women” in class, from one of their modern-day sisters: planet-hunting astrophysicist Dr Lisa Kaltenegger.
Wow, I thought.
Why wasn’t there a movie?
Of course, it was tough enough for women to get their hands on scientific instruments 100 years ago, far less the credit for their work. (Come to think of it, almost all the credit for Rosalind Franklin’s iconic discovery in biology – the crystalline structure of DNA – went to Watson and Crick just 50 years ago, so what’s new).
The Cambridge Science Festival will offer three sessions which celebrate women in cutting-edge science: “Inquiring Minds”, to be held from April 29 to May 1 at the Boston Museum of Science. The dozen speakers represent a remarkable diversity of scientific talent, from marine biology to chemistry and aerospace design.
But, for me, the thread of female scientific genius can be followed just as easily at any of the six astronomy-related events at the Festival, including “80 Years of Astronomy” (April 24), “From the Mysteries of the Brain to the Wonders of the Universe,” (April 24) and “Cambridge Explores the Universe” (May 1).In fact, if they keep their eyes peeled, visitors to the latter – held at the Harvard Observatory – might find the names of two of the women I mention in this blog attached to two of the instruments they’ll get to play with (I ain’t sayin which).
“Cambridge Explores the Universe” is likely to be the most family- and fun-oriented of the astronomy events, with telescope tours, planetarium shows and even the chance to operate a robotic telescope at the MicroObservatory during the four hours of the open-house.
But there are some truly jaw-dropping story-lines behind the discoveries made at this place since 1839, and I’m particularly looking forward to the “Scientist Café” – where you’re invited to collar any of the working astronomers over a coffee and get them to give you an insider’s tale.
First, back to 1877: Asked to plot the brightness of stars onto photographic plates, here was the problem that Pickering’s blundering male assistant confronted: the brightness of the star on the photograph didn’t really tell you anything about it.
That’s because – unless it was a very nearby star, like Sirius – you had no idea of knowing how far it was from the earth.
Imagine being asked to measure all the lights from a photograph of an ocean scene on a moonless night.
The brightest one could be a 30 watt flashlight held in a life raft, 10 yards in front of the camera, and the dimmest could easily be a million candle-power lighthouse 3 miles away.
Using a combination of herculean patience and stunning insight, Leavitt discovered a pattern in a variety of star called “cepheids” which revealed their true power.
(Like a bell: the bigger the star, the slower its vibration cycle from bright to dim and back to bright.)
Although exploding stars are now used to measure the farthest distances, “Leavitt’s Law” – the relation between “period and luminosity” -remains the most accurate measuring tape in the universe.
But what about all the other stars? The ones that didn’t vibrate so reliably?
Again, “Pickering’s women” found the answer.
According to Debra Davis – editor of Woman Astronomers – his housekeeper, Williamina Stevens, and her unborn child had been abandoned by her husband just months after arriving in the US, and she was eager to find some means of financial independence.
Formerly a teacher in Scotland, Stevens proved so expert at plotting the brightness of stars on her boss’s photographic plates that she headed a project to survey the entire night sky (funded by another woman of central importance to astronomy: Anna Draper) and was appointed Harvard’s Curator of Astronomical Photographs.
Within 10 years, yet another female colleague, Annie Jump Cannon, invented an efficient new way to classify all stars at Stevens’ urging, and perhaps the most famous string of letters in all of science – “OBAFGKM”- to describe how they are organized.
As it turned out, nature would reward Cannon’s idea with an almost magical symmetry in the way that all “healthy” stars are arranged.
Incredibly, stars which are divided into groups of OBAFGKM (our Sun is a “G” star) by the fingerprint-like characteristics in their light, called “spectral lines”, can be arranged exactly the same way no matter if you’re dividing them by their size, their color, their total power output; their mass, their temperature, or even their life expectancy. (So all “O” stars will live shorter lives than all B stars, which will live shorter lives than A stars, etc. And O stars will also be bluer in color (And hotter. And bigger) than B stars, which will be bluer in color (And hotter. And bigger) than A stars, etc, etc.)
So that’s the distances and types of stars taken care of by Pickering’s pioneers.
But what about what they’re actually made of? (And most of the universe, for that matter)
Within three years of her arrival in Harvard from England – but working for Pickering’s successor – Cecilia Payne stunned the science world with an answer no one could challenge.
While her male counterparts had long insisted they were mostly made of iron, Payne proved it was hydrogen.
Other aspects of her research would form the foundation of the modern picture of how planets form, and how the elements are made.
And yet Payne was rated no higher than a “technical assistant” by her male director for 13 years after her groundbreaking discovery.
In the end, the pieces of knowledge we have about Harvard’s women astronomers are a lot like the faint points of starlight on their telescope plates: the blurred and often overlooked evidence of searing power.
I’d really welcome any comments or additional info folks might have about female astronomers.
Next week: I reveal how visitors will come face to face with a real, working time machine at the Festival.
Thanks for reading; cheers – Rowan
* (Rowan Philp is a Knight Science Journalism Fellow at MIT)