Cosmos: A Spacetime Odyssey, Episode 8, “Sisters of the Sun”

In earlier episodes, Cosmos has conspicuously missed opportunities to highlight the scientific contributions of women. I found that all the more perplexing because it’s co-written by Ann Druyan, whom we know is attuned to feminist issues. In fact, it’s because of her that Cosmos even has that title: Carl Sagan originally wanted to call it “Man in the Cosmos”, until she persuaded him otherwise by pointing out the sexist assumption.

But this episode took a big stride toward redressing that balance. In an excellent animated sequence, it showed the Harvard women who inaugurated modern astronomy: especially Annie Jump Cannon, who classified hundreds of thousands of stars (!) based on the absorption lines in their spectra (i.e., the Fraunhofer lines from an earlier episode). The stellar classification scheme that Cannon worked out is still used by astronomers today. And this was all in an era before computers, when doing astronomy meant poring over photographic plates with a magnifying glass to analyze every faint smudge of light. The episode did an admirable job of showing the women’s diligence and devotion, although it could have also mentioned how little they were paid for it: 50 cents an hour or less, the wage of an unskilled laborer by the day’s standards.

We then met Cannon’s successor Cecilia Payne, who came to Harvard because it was one of the few places where women were able to research and not just to teach. And her contributions were even greater: she realized that Cannon’s taxonomy of stars was actually a chart of stellar temperatures, from hot blue giants to midrange yellow stars like our sun to cool red dwarfs. In her thesis, she went against conventional wisdom by arguing that stars were made mostly of hydrogen and helium, contradicting the prevailing belief that they contained the same proportions of rocky elements as the Earth, but heated to incandescence. She met with such resistance that she watered down her thesis, but her original conclusion was ultimately proven right.

This was a strong argument for gender equality, but it could have been even stronger. For instance, Cannon’s collaborator Henrietta Swan Leavitt got a brief scene, but what wasn’t mentioned was that she studied Cepheid variable stars, establishing the relationship between their period and their intrinsic brightness. This made them one of astronomy’s first standard candles – and that fact was used by Edwin Hubble to prove that what astronomers then called “spiral nebulae” were actually other galaxies, far beyond and separate from our own Milky Way.

The Spaceship of the Imagination was used to excellent effect in this episode to show the life cycles of stars, touring luminous star-forming nebulae and ghostly stellar remnants. Tyson himself, usually a cheerful, larger-than-life host, narrated this part with a hushed, reverent air. It worked well, especially in the standout segment where he showed how the Sun will die: in the far future, it will exhaust its hydrogen fuel and swell into a red giant as it begins burning helium, consuming the inner planets. When that too is used up, the Sun will puff off its outer layers and become a white dwarf, a cool, dense cinder.

But larger stars have a more violent fate in store: they die in supernovae, becoming neutron stars or black holes. The episode closed with the gigantic star Eta Carinae, about 7,000 light-years from us, which will one day explode in a cataclysm so enormous that it will not only be visible from Earth, it could briefly become full-moon-bright in the night sky. We’ll just get a light show, but any inhabited planets too near could be scoured clean by radiation.

Although some of this was already covered in earlier episodes, I won’t complain when the presentation is as strong and elegant as it was here. This was an outstanding episode, made even better by several callbacks to the original Cosmos, including an echo of the “glorious dawn” line that was turned into a music video by Symphony of Science.

My hope is that this won’t be the only episode to feature the scientific contributions of women. From Lynn Margulis (Carl Sagan’s ex-wife!) to Emmy Noether, there have been countless female scientists who made groundbreaking discoveries and whose stories deserve to be told. It would be a powerful way to drive home the point that science, although it’s a human endeavor and inherits all the frailties of humanity, is also the only system of thought that ultimately depends on evidence and not on authority, which makes it an unsurpassed tool for demolishing prejudice.

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