How We Discovered the Life Cycles of Stars, on Cosmos

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The theme for this week's episode of Cosmos was the life cycle of stars, beginning with the famous Pleiades star cluster. But this episode truly belongs to a cluster of stars from the world of science: astronomer Annie Jump Cannon and her colleagues, who developed Harvard's stellar classification scheme.

Image via NASA, ESA, AURA/Caltech, Palomar Observatory


After our introduction to the Pleiades, we move on to the work of Harvard astronomer Edward Charles Pickering and the team of researchers he hired to help him study stellar evolution, led by Annie Jump Cannon and Henrietta Swan-Leavitt. Pickering and his "computers" developed the stellar classification system still in use today.

That a name as awesome as "Annie Jump Cannon" isn't known to every school kid might be attributed to the sexism of her age...and ours.


But all is not lost for the women of astrophysics. When Cecilia Payne-Gaposchkin, who pursued her PhD at Cannon and Swan-Leavitt's lab, predicted against the accepted wisdom of the day that stars would have much more hydrogen and helium than metal, her thesis was rejected by the experts and she was forced against her better judgement to recant her own most significant findings. Evidence, however, is the great equalizer in science and when the evidence showed that Dr. Payne's theory was correct, she was given full credit for the discovery and her thesis has become part of the canon of western scientific knowledge.


After this lesson in scientific history, Tyson takes the Ship of the Imagination on a tour of the different kinds of stars in the galaxy. The lives of stars are determined by their mass and dominated by gravitational collapse and nuclear fire.

Stars like our own sun have enough gravity to fuse light elements into heavy, but not enough to overcome the repulsive forces between the electrons in its core. After expanding into red giants and casting off butterfly-like shrouds of planetary nebulae, they collapse down to white dwarfs that smolder for hundreds of billions of years afterwards. Other, heavier stars, are dense enough to overcome the repulsive force of electrons and die in dramatic supernova explosions, spreading heavy elements through the galaxy and leaving behind small, city-sized neutron pulsars. Still heavier stars have enough gravity to overwhelm all atomic forces and collapse into black holes or, rarer still, explode into hypernovae with enough energy to destroy planets in neighboring star systems.


In describing the birth, life and firey death of our stellar sisters, Tyson reiterates Sagan's famous observation that, me and everyone who's ever lived from Annie Jump Cannon to Dr. Cecilia Payne...are all made of star stuff, though Tyson prefers the more Bowie-esque term "stardust."

With all their explosive power, the nuclear-fueled furnaces that populate the heavens are the true engines of creation. It's the most awe-inspiring observation made in either version of Cosmos that we are all literally part of the life cycle of the galaxy itself. We are the cool, heavy ash of long dead stars, warmed by the heat of our sun, combining, recombining and finally blinking awake to see ourselves written in the twinkling jewels of the night sky.


From the ancient Greeks imagining Orion chasing the Pleiades across the sky, to Pickering, Cannon and Payne analyzing the composition, arrangement and age of our stellar neighbors to our own modern understanding of our place in the cosmos, science has shown us that the wonders of our origins lie not just in ourselves, but in our stars.