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(This program is no longer streaming). Leonardo da Vinci was a Renaissance genius. Not only did he paint masterpieces of art, but he was an obsessive scientist and inventor, dreaming up complex machines centuries ahead of his time, including parachutes, armored tanks, hang gliders, and robots. On the 500th anniversary of Leonardo’s death, with the help of biographer Walter Isaacson, NOVA investigates the secrets of Leonardo’s success. How did his scientific curiosity, from dissections of cadavers to studies of optics, shape his genius and help him create perhaps the most famous painting of all time, the "Mona Lisa"? (Premiered November 13, 2019)

Discover the science behind Leonardo da Vinci's masterpieces—and Mona Lisa's iconic smile.

Decoding da Vinci

In a new age of information, rapid innovation, and globalization, how can we prepare our children to compete? Once the envy of the world, American schools are now in trouble. Test scores show our kids lag far behind their peers from other industrialized countries, and as the divide between rich and poor grows wider, the goal of getting all kids ready for college and the workforce gets harder by the day. How can the latest research help us fix education in America? Can the science of learning—including new insights from neuroscientists, psychologists, and educators—reveal how kids’ brains work and tell us which techniques are most likely to engage and inspire growing minds? What role should technology play in the classroom? Teachers, students, parents, and scientists take center stage as NOVA explores a new vision for the “School of the Future.”

How can the science of learning help us rethink the future of education for all children?

School of the Future

Rockets are becoming cheaper and more powerful than ever before thanks to stunning new technologies. As companies like SpaceX and Virgin Galactic make space more accessible, and NASA returns to crewed spaceflight, a new era of space exploration seems to be on the horizon. But will this seeming rocket Renaissance become more than just hype? NOVA explores the latest rocket technologies and the growing role private citizens may have in space. (Premiered February 13, 2019)

With new technologies, NASA and private companies are promising a new renaissance in space travel.

Rise of the Rockets

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How Engineers Soundproof a New Underground Train Track

Part of the new London track is directly below an iconic performing arts center.
Construction teams use springs to quiet the Elizabeth Line trains as they pass under a concert hall.
How Engineers Soundproof a New Underground Train Track Published January 31, 2023Narrator: Once the trains start running, these tunnels will be noisy. But right here, the project faces one of its most difficult construction challenges. The team needs to reduce the amount of noise coming from this section of track.Gregg Purcell: Here we are directly beneath the Barbican, right directly beneath.Narrator: Opened in 1982. The Barbican Center is an international hub for arts and culture. London&#x27;s equivalent of Carnegie Hall. The center&#x27;s largest venue, Barbican Hall, sits one story below ground.Huw Humphreys: Barbican Center is, the home of the London Symphony Orchestra, presents regular seasons from the Royal Shakespeare Company. It really is one of the truly great artistic centers in the UK. A lot of music is about exploring the relationship between the very quietest sounds and silence. And therefore a lot of performances really focus on that magical area of audibility.Narrator: And that&#x27;s the problem. Barbican Hall sits just 55 feet above Crossrail&#x27;s tunnels. Noise or vibrations from trains could travel through the earth and into the concert hall. Disturbing performances. To guard against this. Crossrail engineers are using ingenious floating tracks, unique concrete slabs of rail track that sit on special springs. As a train passes over these springs, they should absorb most of the energy and reduce noise reaching the theater.Gregg Purcell: Floating tracks that allows that noise to be brought down even lower on the surface. You won&#x27;t hear anything when you&#x27;re watching Hamlet.Narrator: It takes over 150 tons of concrete reinforced with steel bars to form each hundred foot long floating track slab.Gregg Purcell: We&#x27;ve got all the reinforcements complete. These spring houses are all installed. We&#x27;ve got all the rail. And this slab has been set up to pass the concrete on top. That&#x27;s the liquid gold coming out there.Narrator: Once set, they screw the springs into place on the underside of the slab and raising to its final height. With the slabs now cushioned by the springs, they can set the rails on top. With this crucial section of the railway in place, the team can pick up the pace and lay track throughout the rest of the tunnels.

Part of the new London track is directly below an iconic performing arts center.

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The Claude "Bud" Lewis Carlsbad Desalination Plant near San Diego uses reverse osmosis filtration to provide 50 million gallons of desalinated seawater per day. ​Image Credit: Reed Kaestner, Getty Images

Why it's so hard to make salt water drinkable

Water covers nearly three-quarters of Earth’s surface, yet only about 2.5% of it is fresh water. And the rising demand, coupled with climate change and drought, has put an increasing strain on the freshwater supply in some areas. So why not just remove the salt from–or desalinate–ocean water for human use? Well, it’s easier said than done. 
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Seawater is on average 140 times saltier than drinking water. To efficiently remove those salts, desalination plants use specialized techniques that largely fall into two categories: thermal desalination and reverse osmosis. Thermal desalination involves heating seawater to its boiling point and condensing the salt-free steam for drinking water. Though there’s a range of efficiency in both methods, thermal desalination requires roughly 10 times as much energy as reverse osmosis, says Emily Tow, a mechanical engineer at Olin College of Engineering who studies water desalination and reuse. Most desalination plants today use reverse osmosis. In this process, seawater is pushed through a membrane to remove the salts. “The membranes are so fine that water can get through, but salts really can't,” Tow says, and the clean water that comes through is taken for drinking water. Although this method requires less energy than thermal desalination, it still uses quite a bit of electricity, about “four times what we would typically spend on our municipal water use, including wastewater treatment,” Tow says. But for every gallon of seawater that plants process through reverse osmosis, only half is recovered as fresh water. That’s because the process has a built-in trade-off: As water is pushed through the membrane, the seawater on the starting side gets more concentrated, which makes it even harder to pass through the membrane. This, in turn, increases the energy needed to push the water through.
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The super-concentrated seawater that's left over, called brine, is a common byproduct of reverse osmosis plants. Once the filtration is done, plants typically pump the brine back into the ocean, far away from shore, while mixing it with seawater so it doesn’t create extra salty zones. Some researchers <a href="https://www.sciencedirect.com/science/article/pii/S0011916417307750">have pointed out</a> that having multiple plants in one area operating for an extended period could lead to an increase in ocean salinity and negatively affect the surrounding ecosystem. But with proper design and monitoring the effect should be minimal.Although seawater is plentiful, removing the salt is an energy-intensive process that may only make sense in specific scenarios. “Our need for water as humans is never-ending, but our supply of fossil fuels is limited,” Tow says.One way to bring down desalination energy costs is by coupling plants with <a href="https://www.pbs.org/wgbh/nova/article/solar-desalination/">renewable energy sources</a>. “Wouldn't it be great if anytime you build a new seawater plant you have to build enough renewable energy capacity to power that plant,” Tow says, “so that we're not just making things worse for the environment while we solve our short-term water problem.”
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Seawater might seem like an obvious solution to water scarcity, but it comes at a cost.

How Computer Algorithms Make Predictions

Can we rely on them to be fair?
These computer programs use artificial intelligence to look for patterns in data without human instruction.
How Computer Algorithms Make PredictionsPublished January 18th, 2023NARRATOR: We live in a world of big data where computers look for patterns in vast collections of information in order to predict the future, and we depend on their accuracy. Is it a good morning for jogging? Will this become cancer? What movie should I choose? The best way to beat traffic? Your computer can tell you. Similar computer programs called predictive algorithms are mining big data to make predictions about crime and punishment, reinventing how our criminal legal system works. How do these predictions actually work? At the core of these programs is software, which, like all computer programs, is built around an algorithm.VIVIENNE MING: One way to think about our rhythms is to think about the hiring process. In fact, recruiters have been studying for 100 years, and it turns out many human recruiters have a standard algorithm. When they&#x27;re looking at a resume. So they start with your name. And then they look to see where you went to school. And then finally they look at what your last job was. If they don&#x27;t see the pattern they&#x27;re looking for. That&#x27;s all the time you get. And in a sense, that&#x27;s exactly what artificial intelligence is doing as well on a very basic level. It&#x27;s recognizing sets of patterns and using that to decide what the next step in this decision process should be.NARRATOR: What is commonly referred to as artificial intelligence or A.I. is a process called machine learning, where a computer algorithm will adjust on its own without human instructions in response to the patterns it finds in the data. These powerful processes can analyze more data than any person can and find patterns never recognized before.LATANYA SWEENEY: All of these different types of machine learning algorithms are all trying to help us figure out are there some patterns in this data? It&#x27;s up to us to then figure out, are those legitimate patterns? Are they useful patterns? Because the computer has no idea. It didn&#x27;t make a logical association, it just made it made a correlation.

Can we rely on them to be fair?

The top half of Jupiter in blue and green against a night sky

A composite image of Jupiter using images captured by the James Webb Space Telescope. Image Credit: NASA, ESA, CSA, Jupiter ERS Team; image processing by Judy Schmidt.

NOVA’s most popular science documentaries of 2022

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The past year brought shocking and awe-inspiring stories from the world of science–and NOVA was there. From the most ambitious telescope ever built to an accident that paralyzed the world economy, we bring you the five most-watched documentaries NOVA released in 2022. 
<h3>Arctic Sinkholes</h3>Colossal explosions shake a remote corner of the Siberian tundra, leaving behind massive craters. In Alaska, a huge lake erupts with bubbles of inflammable gas. Scientists are discovering that these mystifying phenomena add up to a ticking time bomb, as long-frozen permafrost melts and releases vast amounts of methane, a potent greenhouse gas. What are the implications of these dramatic developments in the Arctic? Scientists and local communities alike are struggling to grasp the scale of the methane threat and what it means for our climate future.
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<h3>Ultimate Space Telescope</h3>Follow the dramatic story of the James Webb Space Telescope—the most complex machine ever launched into space. If it works, scientists believe that this new eye on the universe will peer deeper back in time and space than ever before to the birth of galaxies, and may even be able to “sniff” the atmospheres of exoplanets as we search for signs of life beyond Earth. But getting it to work is no easy task. The telescope is far bigger than its predecessor, the Hubble Space Telescope, and it needs to make its observations a million miles away from Earth—so there will be no chance to go out and fix it. That means there’s no room for error; the most ambitious telescope ever built needs to work perfectly. Meet the engineers making it happen and join them on their high stakes journey to uncover new secrets of the universe. 
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<h3><a href="https://www.pbs.org/wgbh/nova/video/why-ships-crash/">Why Ships Crash</a></h3>When the bow of the colossal Ever Given container ship plowed into the bank of the Suez Canal on March 23, 2021, international supply chains ground to a halt. What went wrong? Follow the dramatic efforts to free the ship and the investigation into one of the most expensive shipping disasters ever. Maritime experts analyze other recent accidents and try to figure out how such devastating crashes could be prevented.
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<h3><a href="https://www.youtube.com/watch?v=LS7ChlsZsGI&amp;list=PLtiOgIRVt4053SXtk0cVIIkhFfbfkac0e&amp;index=3&amp;t=7s">Ice Age Footprints</a></h3>When and how did humans first arrive in North America? A new discovery has upended archaeologists’ theories: Thousands of ancient footprints that stretch for miles across New Mexico’s White Sands National Park, capturing moments when Ice Age humans encountered now-extinct beasts, including mammoths and enormous ground sloths. These footprints tell an intimate story about what life was like during the Ice Age and reveal surprising new evidence about when humans arrived in North America. 
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<h3><a href="https://www.pbs.org/wgbh/nova/video/nazca-desert-mystery/">Nazca Desert Mystery</a></h3>One of the world’s greatest ancient enigmas, the Nazca lines are a dense network of crisscrossing lines, geometric shapes, and animal figures etched across 200 square miles of Peruvian desert. Who created them and why? Ever since they were rediscovered in the 1920s, scholars and enthusiasts have raised countless theories about their purpose. Now, archaeologists have discovered hundreds of long-hidden lines and figures as well as evidence of ancient rituals, offering new clues to the origins and motivations behind the giant desert symbols.
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Explore the cosmos, delve into ancient history, and follow an extreme rescue with NOVA’s most-watched documentaries released in 2022.

Joe Watkins and Kim Charlie speak with Kirk Johnson in White Sands National Park

Modeling Ice Age Technology | Ice Age Footprints

Footprints at White Sands help Native Americans learn about their history and deepen their connection to the land.

Saving Notre Dame’s Iconic Stone Vaulting

Geologists attempt to restore limestone at Notre Dame Cathedral after a fire.
The water used to fight a fire at Paris’s iconic Notre Dame Cathedral and months of rainwater damaged the Cathedrals’ stonework but a team of geologist have a plan to save it.
Saving Notre Dame’s Iconic Stone VaultingPublished December 22, 2022NARRATOR: On April 15, 2019, the 856-year-old cathedral of Notre Dame de Paris is undergoing a six-and-a-half-million-dollar renovation of the spire, when a fire breaks out inside the oak framework of the roof. After 90 minutes, the 400-ton timber and lead spire gives way and crashes through the stone vaulting. The fire destroys the roof and spire and leaves three gaping holes in the vaulting. With the loss of the roof and no protection from the elements for almost two years after the fire, the exposed stone vaulting was repeatedly soaked by rain. In the 18th and 19th centuries, restorers cast layers of plaster on top of the vaulting in case of a fire. This protected the stonework from the heat of the 2019 inferno, but not from the water used to fight it. This, along with months of rainwater, washed salt from the plaster into the lower layers of the porous limestone. As the moisture evaporates, the salt crystalizes and forces the limestone apart, destroying the inner surface of the vaulting. Geologist, Véronique Vergès-Belmin, will use a technique to draw the salt out from the stone. To extract the salt, Véronique’s crew will coat the vaulting with a paste of clay, sand and purified water, known as a poultice. The water from the poultice is drawn into the stone, where it dissolves the harmful salt crystals. As the clay of the poultice dries, it draws the salt water out of the stone, saving the vaulting from further damage.VÉRONIQUE VERGÈS-BELMIN: The poultices will be removed when they will all have dried.NARRATOR: They load the sticky mixture into a compressed air gun and spray it into every crevice. Finally, they carefully smooth the poultice across the areas affected by the salt damage.VÉRONIQUE VERGÈS-BELMIN: You can see that it follows very, very closely the surface of the stone. And what we recommend is that poultice should not be thicker than half a centimeter to one centimeter, otherwise there are risks that it falls down. We need to have a very slow process until the vaults are dry. But this will take time, much time.NARRATOR: The poultice may stay in place until the new roof is built and the vaulting is permanently protected from rain and snow.

Geologists attempt to restore limestone at Notre Dame Cathedral after a fire.

Restoring Notre Dame's Iconic Stained Glass

Glass experts uncover the South Rose window’s hidden past.
After the fire, the team working on restoring the South Rose window noticed major changes to the original stained glass masterpiece.
Restoring Notre Dame&#x27;s Iconic Stained Glass Published December 9th, 2022 NARRATOR: Inside Notre Dame, the first chance to get up close to the gigantic South Rose Window in 160 years…GLASS EXPERT: (In french) This bit here, is it too old, or...?NARRATOR: …has revealed a mystery.KARINE BOULANGER: We only have 13th century glass and 19th century glass. In the 19th century, they removed everything that wasn’t 13th century, and then they had to do new panels, if a panel was missing.NARRATOR: The chief suspect for these radical changes to the window is architect Eugène Viollet-le-Duc. In the 1840s, he was tasked with breathing new life into Notre Dame. At the time, it was not the beloved building we know today. The cathedral was ransacked during the French Revolution; statues of biblical kings on the facade were decapitated; and it was used as a warehouse, sitting derelict and unloved for decades. During his restoration, le-Duc removed all glass in the South Rose Window that was not original and replaced it with modern glass. Elisabeth is also finding that he made significant alterations to some of the original glass panels.NARRATOR: Why did le-Duc alter the window? The glass experts hunt for clues here at the Paris Médiathèque of Architecture and Heritage. They hope le-Duc’s plans for the South Rose Window shed light on his thinking.NARRATOR: As they dig into the archives, they make a breakthrough.KARINE BOULANGER: We just discovered that there was a change of structure. Before Viollet-le-Duc, there was an iron reinforcement in the center of the rose. But obviously it wasn’t enough. So, Viollet-le-Duc put it further away from the center. And when you removed the iron work here, he had to change the form of the panels.NARRATOR: Le-Duc’s restoration was sweeping. He removed a smaller structural ring of iron and replaced it with a bigger ring to strengthen the core of the window; he removed all traces of previous restorations, to replace them with panels of new glass; and he rotated the whole window 15 degrees to make it structurally stronger.KARINE BOULANGER: The problem must have been that the mediaeval rose wasn’t stable in its axis. That must have been the problem.NARRATOR: Le-Duc’s major changes to the South Rose were motivated by more than mere aesthetics. Strengthening the window has helped preserve this masterpiece.

Glass experts uncover the South Rose window’s hidden past.

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