Cosmos: A Spacetime Odyssey Recap - Episode 8

Season 1, Episode 8 -- "Sisters of the Sun"

Our Galaxy - The Milky Way
The Milky Way. Getty Images/Elena Pueyo

Episode 8 of the series starts off with our fearless host, Neil deGrasse Tyson, aboard the Ship of the Imagination telling us we pulled the stars from the skies and brought them down to Earth, but at what cost? We see several cities like Paris and Rome with bright lights lit up at night. Tyson tells us the cost for all of the lights is the stars and we cut to the intro music and visual sequence.

Tyson sits near a campfire and tells us a long time ago, our relationship with the stars was much more personal.

We watched the stars like our lives depended on it -- because they did. We see computer animations connecting the stars into various constellation patterns as Tyson tells us that humans were not the fastest, strongest, or biggest animals we compete against. However, we have intelligence and can recognize patterns.

The entire series is available to stream via Netflix, as well as on Blu-Ray and DVD.

The Constellations' Stories

Over time, our ancestors figured out that the stars changed in regular patterns that foretold changes in the Earth that could either help or hurt our survival. Before there were electronic devices, every human culture connected the dots of the stars to create a sort of survival manual.

Even though the names of these pictures of animals, heroes, or even farm animals in the sky varied between cultures, there was one particular group of stars called the Pleiades. They formed about 100 million years ago and each is 40 times brighter than our Sun and the one named Alcyone outshines our Sun by 1000 times.

If you could see at least 6 Pleiades, you were considered normal. If you could see 7 or more then you were an ideal candidate to be a warrior or a scout in ancient civilizations. They were believed to have a haunting significance. When they reach the highest point in the sky, it was thought that spirits would roam around in the dark on Earth.

This is thought to be the origins of what we now call Halloween.

All over the Earth, these cultures had stories to explain how the Pleiades came to be. The Kiowa tribe of North America are then animated to tell their story. Some young women sneak away from the camp site to dance freely amongst the stars. They are interrupted by a large pack of bears that chase them as they run away. One prays that a rock they climb up on save them and take pity on them. The rock heard her cries and grew until it became what is known as Devil’s Tower and the maidens on the rock became what is now the Pleiades which can be seen directly above the tower in mid winter.

The Ancient Greeks also saw the seven stars as the seven daughters of Atlas. An animation shows the hunter Orion spying on the daughters as he becomes mad with desire for the women. For seven years he chased them relentlessly until they became exhausted and prayed to Zeus for help. The King of the gods took pity on them and transformed them into the Pleiades. Orion was later also put in the stars by Zeus where he could continue his chase of the sisters for all eternity.

Tyson tells us our ancestors wove beautiful stories, but they can bring us no closer to the stars.

It another few thousand years until 3 brilliant scientists unlocked the true science behind the science of the stars.

Women and Astronomy

After commercials, we see a black and white photo of Harvard in 1901. It was a man’s world then, but an astronomer named Edward Charles Pickering broke that rule. Back in an animation, a man is showing others around a building in Harvard as he tells them Pickering’s “computers” were just down the hall. He opens the door to find a room full of women working away. The men joke about the women not being computers, but actually Pickering’s harem.

Pickering had assembled these women to map and classify the stars. One of them provided the key to understanding what the stars are made of while another devised a way to calculate the size of the universe. Tyson tells us even though they did these amazing things, we’ve probably never heard of either of them.

Annie Jump Cannon was the leader of the team and she cataloged a quarter of a million stars. She had lost her hearing due to scarlet fever when she was younger. Another brilliant female scientist, Henrietta Swan Levitt, was also deaf, but she discovered the law we still use to figure the distance to the stars and the size of the cosmos itself.

Cannon sent out a Christmas card explaining what she and the other women were doing. The light from a star falls through a prism in a telescope to magnify it. The starlight is split into colors of the spectrum of the star. They could then compare the patterns given from the stars to figure out that they were made of the same elements we have on Earth. This allowed them to classify and catalog the type of stars.

It took Cannon decades to study the spectrums of hundreds of thousands of stars and categorize them into one of 7 broad categories she had defined. Each category had its own letter, but even stars in the same category could differ in very minute ways. She learned to recognize these small differences from memory and could further classify them with a number to distinguish them from the others.

In England in 1923, women were forbidden to attain advanced degrees in the sciences. However, Cecelia Payne had attended a lecture by astronomer Sir Arthur Eddington. He was the first to provide evidence that Einstein’s Theory of Relativity was correct. From that point on, she was determined to live out her dreams. She immigrated to the United States where women were now welcome to study the stars.

She was accepted to Harvard and what she discovered there would challenge one of the central beliefs of Astronomy and start a new field called Astrophysics.

Back in the animation of Harvard after the break, Annie Jump Cannon and her team were still cataloging and classifying stars. They were just dots on paper whose purpose had not yet been discovered. Cecelia Payne joined the group of women working on the project. She had never experienced such kindness and willingness to share findings in science before. This “sisterhood” had done the legwork and Payne turned their findings into a radical new understanding of the stars.

The two women became great friends. Cannon taught Payne everything she knew about spectra of the stars and Payne began to analyze Cannon’s data. Her expertise in theoretical and atomic physics allowed her to figure out the exact chemical composition and physical state of the stars. The most prominent feature of the stars showed heavy elements like calcium, iron, and the most abundant elements on Earth. They concluded that the stars were made of the same things as Earth in roughly the same ratios.

In 1924, Henry Norris Russell was the dean of American astronomers. He made major contributions of what we understood about stars. Payne sits in the audience listening to Russell give a speech about how the Sun has 40 of the same elements that Earth has. Therefore, he concludes, the Sun must be made of the same things as the Earth and if we would heat the Earth up, its spectra would resemble the Sun’s.

Payne figured out from this speech that she could use Cannon’s data to figure out exactly how hot each star is based on its spectra. The letters that designated which group the stars belong was actually a temperature scale from the hottest to the coldest. Payne concluded that stars are made of mostly hydrogen and helium and that there is about a million times more hydrogen and helium in the stars than there are heavy metals. Cannon asked if anyone else had checked her calculations, but Payne had already sent off her thesis to Russell with her findings.

As Russell read her thesis, he felt sorry for her, deciding her thesis was severely flawed. He writes a letter to her and when she receives and reads it, she was distraught to see he disagreed and that there is no way hydrogen could be a million times more abundant than metals in stars. This made her begin to doubt herself and the quality of her data. She caved and added a sentence to her thesis that undermined all of her work.

It wasn’t until four years later that Russell realized Payne had been right all along. He did admit it, as soon as he realized he was wrong and gave Payne all the credit for the discovery. That thesis was arguably the most brilliant ever written in Astronomy and became the standard text in its field. Payne says she was to blame for giving in to authority when she believed she was right. She tells others reading her book to defend their facts and push their position if they are sure. This research made it possible to learn the stories of the stars all the way back to their beginnings.

Life of a Star

We come back from commercial and are back on the Ship of the Imagination. Tyson tells us there are many types of stars. Some are bright like our Sun and some are very dim. The greatest stars are 10 million times larger than the smallest ones. Some are over 10 billion years old and others are being born right now.

When atoms fuse, they make starlight. Stars are born in “litters” from the gas and dust of interstellar clouds. The masses of the stars in the litter range from the runts that would be about the size of our largest planets to the biggest of the bunch that dwarfs the Sun.

The stars in the nebula under Orion’s belt are considered “newborns” since they are only about 5 million years old and still encased in the gas and dust that created them. The Pleiades are considered “toddlers” at about 100 million years old. They have shed their blankets of dust, but are still bound together by gravity. They will eventually break away from each other and go their separate ways.

Most of the stars in the Big Dipper would be “adolescents” at about half a billion years old. They have drifted from their birth cluster, although we can trace their ancestry. They will also drift away from each other as time passes. In fact, most of the constellations we see are made up of unrelated stars that could be bright and nearby, or faint and far away. 

From space, even though our Sun is the closest star to us, it is hard to identify. It is a middle aged star and it is far away from its siblings that were born in its litter. They are now dispersed throughout the galaxy. Many of them have their own planets. Some of them may even nurture their own evolution of life on those planets.

Death of a Star

Most stars in the sky orbit around one or more stellar companions. We usually cannot see the dimmer of the stars in the set with the naked eye. A world of three Suns may rarely have nights and the days could alternate between red and blue light. It is the destiny of stars to collapse. Of the thousands you see in the night sky, they are alive and between two collapses. Their first collapse is what forms them and then their final collapse will extinguish their illumination.

Gravity makes stars collapse unless something else intervenes. Our Sun is a huge ball of incandescent gas. The super hot gas in the core pushes it outward as gravity crushes it inward. The Sun is in a stable equilibrium between these two forces and this will be maintained for another 4 billion years. As the Sun consumes hydrogen, its core shrinks and the gas pushes outward slightly. It takes millions of years to see any change. In about a billion years, the Sun will be about 10% brighter than it is today. It might not sound like much, but that extra heat will make a huge impact on Earth.

When the Sun runs out of hydrogen to fuse, its gas will cool and pressure will fall. The interior will not be able to support the outer layers and the Sun will die. Helium has built up in the core. With no fire to sustain its weight, it will collapse in on itself until it gets hot enough to fuse helium into oxygen and heavier metals. The core would be much hotter than it is now. The atmosphere would rapidly expand until becomes 100 times its original size.

That form of the Sun will be a Red Giant. It will become so big that it will devour the planets, Mercury and Venus. It could even possibly engulf the Earth. Once the Sun burns through the helium, it will be unstable and it will begin to cast off its outer layers into space. The exposed super hot core will flood the surroundings with large amounts of ultraviolet light.

The Sun will collapse like a soufflé until it’s about the size of the Earth. It will be so dense that the electrons will push back to keep it from getting any smaller. There will only be a single point of light in the center. This White Dwarf star will go on shining dimly for another 100 billion years. Would future beings seeing it understand the amount of life it once sustained?

Back from commercial, we are cruising on the Ship of the Imagination away from the Sun. Tyson tells us the psychedelic death clouds of stars are fleeting. They only last tens of thousands of years before dissipating into space where they can be used to make new stars. Other types of stars, like those in a binary star system, have different life paths.

Sirius, the brightest star in our night sky, has a dim White Dwarf companion. When Sirius becomes a Red Giant, it will shed its skin onto its companion. The intense gravity of the White Dwarf will pull that in and when it hits the star, it will trigger nuclear explosions. The greatest bursts, called novas, will give off 100 thousand times more energy than our Sun.

A star about 15 times more massive than the Sun, such as Rigel, the blue supergiant that forms Orion’s right foot, has a different fate. The electrons cannot keep the star from collapsing in on itself until the nuclei get so overcrowded that they push back. Rigel will shrink about 100 thousand times until it can shrink no more.

At that point, it ignites a more powerful nuclear reaction called a supernova. Most stellar evolution takes billions of years, but the trigger for a supernova can happen in seconds. All that will be left will be a rapidly rotating neutron star called a pulsar that will be about the size of a city.

A star about 30 times bigger than the Sun, like Alnilam in Orion’s belt, there will be no stopping its collapse. When it runs out of fuel, it will also go supernova. This explosion will be so massive that not even nuclear forces will be able to hold off its collapse. Nothing can withstand such gravity and such a star has an astonishing destiny. It will continue to collapse and crossing a boundary in spacetime called the Event Horizon. We cannot see past the Event Horizon and the star will be inside a black hole where not even light can escape.

There is one star in our galaxy that is so massive that it won’t go nova or supernova, but instead something so catastrophic that it has been named a hypernova. This may even happen in our lifetime.

The Night Sky

We then travel to the Australian Outback where there are no cars and no lights, so we can get a good view of the Milky Way in the night sky. The center of our galaxy rises high in the sky. We live in a spiral galaxy and we’re seeing light from billions of stars in that disk. The sky is not a continuous blanket of light. There are dark patches in the sky caused by interstellar dust. The dust blocks the starlight. Most cultures looked up at the stars and connected to dots of light to form familiar pictures. The Aboriginal people of Australia instead saw patterns in the darkness throughout the Milky Way. They saw an emu in the absence of stars.

There are so many ways to look at the night sky. For a million years, we’ve been watching the night sky. Supernovas occur in our galaxy about once a century. If we could compress all the nights of stargazing into one minute, this is what we’d see. There is then a computer animation of all the supernovas smattering throughout the sky as the musical score swells.

Tyson tells us if our eyes were telescopes and not limited to one type of light, this is the Milky Way we’d see. We are shown a bright and beautiful picture of the Milky Way as seen through a telescope and again the music swells. Tyson tells us it is a picture of infrared light that shows us tendrils of dust spiraling outward because of supernovas with countless stars in the backdrop.


About 7500 light years away in another part of our galaxy, there is an upheaval on an incredible scale going on. We travel to the Carina Nebula on the Ship of the Imagination. Tyson tells us it is a star making machine. It takes a ray of light 50 years to cross it. The huge stars produced here sear the surrounding dust with their ultraviolet radiation. When a massive star dies, it blows itself to smithereens. The stuff inside blows across the area, just to be gathered up by gravity. In the cosmos, nothing is wasted, but there is an upper limit to how massive a star can be.

When Edmond Halley crossed the equator to make a map of the southern hemisphere sky, Ada Carina seemed like another dim star. However, in 1843, it became the second brightest star in the sky and it’s been flipping out ever since. An expanding dumbbell shaped cloud is the remnants of that explosion. At the center, Ada Carina is unstable and is at least 100 times more massive than the Sun and gives off 5 million times more light. It’s pushing the upper limit of what a star can be. There is also evidence that another massive star, Ada Carina’s twin, is causing even more trouble with its gravity.

The core of a super massive star pours out so much light that it can overwhelm the star’s gravity. If it is too massive, the core pressure will blow it apart. The fate of Ada Carina was determined at its birth. It may have already exploded, as we are looking at light that left it 7500 years ago. When we do see its explosion, it will be unlike anything we’ve ever seen before. It will be a hypernova. It will make a supernova seem like a firecracker. If there are any planets in the area that are harboring life, their days are numbered.

A hypernova will shoot so much deadly radiation into space that even planets up to hundreds of light years away would be stripped of their atmospheres. It would wreak havoc in thousands of nearby star systems. If Ada Carina blows up, what happens to Earth? Luckily, not much will happen. We are 7500 light years away and radiation will fall off rapidly. Still, it will put on quite a show and light up the night in the Southern Hemisphere with the brightness similar to the moon.

We Are Star Stuff

Our ancestors worshipped the Sun. It makes sense to revere the stars because we are their children. The silicon in rocks, oxygen in the air, carbon in DNA, iron in skyscrapers, and silver in our jewelry was made in stars billions of years ago. We are all stardust. How is the energy of the star transformed into everything that happens in our world? When hydrogen fuses in the Sun, they make helium. That energy can wander around for 10 million years in the core until it makes it to the surface. From there, it can flow freely from the Sun to the Earth.

If that energy strikes a leaf, it can be stored as chemical energy. Tyson says it’s “sunshine into moonshine” as he has a glass of wine with an old woman in a vineyard. He says he can feel the energy in the wine turning into electrical energy in his brain that is directing his vocal cords to produce acoustic energy of his voice. Such transformations of energy happen all the time. Energy from our star drives the wind and the waves and the life around us. We are lucky to have this clean energy falling to Earth all around us.

Tyson then picks up his wine to toast to Annie Jump Cannon, Henrietta Swan Levitt, and Cecelia Payne who paved the way for modern Astrophysics and to all of the sisters of the Sun. There is no refuge from change in the cosmos. In 10 or 20 million years from now, it may seem like Orion is about to catch the seven sisters. Before he can get them in his clutches, the biggest stars in Orion will supernova. His pursuit of the Pleiades will finally end and the sisters will peacefully glide away into the cosmos.

We on Earth marvel at the return of our Sun. For a planet orbiting a star in a distant globular cluster a still more glorious dawn awaits. It is not a sunrise, but a galaxy rise of the Milky Way. This galaxy contains all different types of stars and maybe even some we have yet to discover. It is now clear that we are made of the atoms and the stars. Our matter and our form are forged by the great ancient cosmos of which we are a part.

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Scoville, Heather. "Cosmos: A Spacetime Odyssey Recap - Episode 8." ThoughtCo, Sep. 13, 2017, Scoville, Heather. (2017, September 13). Cosmos: A Spacetime Odyssey Recap - Episode 8. Retrieved from Scoville, Heather. "Cosmos: A Spacetime Odyssey Recap - Episode 8." ThoughtCo. (accessed January 18, 2018).