On August 21, 2017, millions of Americans witnessed the first total solar eclipse to cross the continental United States in 99 years. As in all total solar eclipses, the moon blocked the sun and revealed its ethereal outer atmosphere—its corona—in a wondrous celestial spectacle. While hordes of citizens flocked to the eclipse’s path of totality, scientists, too, staked out spots for a very different reason: to investigate the secrets of the sun’s elusive atmosphere. During the eclipse’s precious seconds of darkness, they gathered new clues on how our sun works, how it can produce deadly solar storms, and why its atmosphere is so hot. NOVA investigates the storied history of solar eclipse science and joins both seasoned and citizen-scientists alike as they don their eclipse glasses, tune their telescopes, and revel in the eclipse that spanned the continent.
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Eclipse Over America
PBS Airdate: August 23, 2017
NARRATOR: August 21st, 2017: from coast to coast, Americans witness their first total solar eclipse since 1979. A total eclipse is one of nature's greatest spectacles. It has filled people with wonder since earliest times.
JAY PASACHOFF (Williams College): It's just tremendously exciting to be outside when the universe darkens all around you...
CROWD EXCLAMATIONS OF AWE
JAY PASACHOFF: …and that's a primeval thrill.
NARRATOR: Scientists seize these precious seconds of darkness to explore a region of the sun normally invisible, its outer atmosphere, the solar corona.
JASON KALIRAI (Space Telescope Science Institute): It's this crown around the sun, this beautiful halo.
NARRATOR: The corona is also the source of huge solar storms that can strike Earth with enough energy to plunge cities into darkness.
HOLLY GILBERT (NASA's Goddard Space Flight Center): All of our technology is susceptible to these storms.
NARRATOR: Can we learn to predict when they will occur?
These dangerous solar storms are just one of the mysteries that a total solar eclipse can help scientists to solve. While millions enjoyed the spectacle, scientists were among the most avid eclipse chasers, on the ground and in the air; their goal: to better understand our most important celestial neighbor.
Eclipse over America, right now, on NOVA.
Ninety-three-million miles away from us, the sun is the source of all life on Earth.
JASON KALIRAI: The sun is the most important star to us here on Earth. It's responsible for the warmth that we receive, the food that we eat, the water that we drink. It's essential to our being.
NARRATOR: But every so often, in one of nature's most dazzling spectacles, the sun dramatically disappears.
STEVEN TOMCZYK (High Altitude Observatory of the National Center for Atmospheric Research): A total eclipse, that's almost miraculous.
NARRATOR: Since earliest times, total eclipses have filled people with wonder and dread. The ancient Chinese thought a dragon swallowed the sun. The ancient Babylonians saw them as an omen that could herald the death of a king. But as the age of superstition gave way to an era of reason, scientists discovered a hidden region of the sun, only visible during a total eclipse: its outer atmosphere or "corona."
AMIR CASPI (Southwest Research Institute): The corona has tantalized people ever since it was first observed.
NARRATOR: And mystified them as well, because the corona, the sun's outer atmosphere, is hotter than the surface itself.
AMIR CASPI: It's a few million degrees, much hotter than the surface of the sun. And we don't really understand why that is.
NARRATOR: And, even from millions of miles away, it's dangerous. It can hurl powerful electromagnetic storms towards our planet.
HOLLY GILBERT: When they impact the earth they affect our satellites, they can cause power grids to go down. Because that's where the energy is being deposited from these storms.
NARRATOR: With so much at stake, can we protect ourselves?
BILL MURTAGH (National Oceanic and Atmospheric Administration, Space Weather Prediction Center): We would love to improve our capability to predict this stuff.
NARRATOR: A rare opportunity to unravel these mysteries arrives, with the total solar eclipse, on August 21st, 2017.
10:15 a.m.: Salem, Oregon is plunged into darkness, as the total eclipse begins. Over the next hour and a half, the path of totality sweeps across 14 states. On its way, it blankets the south side of St. Louis, and the whole of Nashville in total darkness, before finally passing over Charleston and heading out to sea.
Astronomers from all over the country have been making feverish preparations for months.
JAY PASACHOFF: We've got the telescopes pointing in the same direction.
NARRATOR: Jay Pasachoff is one of America's most seasoned eclipse scientists.
JAY PASACHOFF: I've now seen 65 solar eclipses. This is number 66. They're just wonderful things to see.
NARRATOR: He is setting up his equipment in Salem, Oregon.
JAY PASACHOFF: There are certainly dozens of telescopes.
NARRATOR: It includes a suite of instruments designed to reveal the hidden structure of the corona.
JAY PASACHOFF: Only on the days of eclipses do we see the corona appear, so we want to take advantage of that as much as possible.
NARRATOR: Farther along the eclipse path, on Casper Mountain, in Wyoming, Steve Tomczyk hopes to find out how the corona triggers those destructive solar storms that can strike Earth.
His team has been preparing for months, but finally they're ready.
STEVE TOMCZYK: So, here we are at Casper Mountain, Wyoming. And the weather is great, and we're getting very excited, as we're leading up to first contact, in about an hour. We have a team of about 15 people that have been working hard. Everybody's ready, the equipment's working, so, we're very excited about our prospects for getting some good data.
NARRATOR: But what if it's cloudy over Southern Illinois? Scientist Amir Caspi has a plan. Two NASA jet aircraft, fitted with telescopes, will fly at 50,000 feet above the clouds, to ensure a clear view. But there are no guarantees.
AMIR CASPI: I'm very nervous. It's game day. It's hard to describe how I feel.
NARRATOR: He hopes his data will shed light on why the corona is so much hotter than the surface of the sun.
All three teams are taking advantage of an extraordinary astronomical fluke. A total solar eclipse occurs only when the earth, moon and sun are perfectly aligned, so the moon blocks the sun's light.
The diameter of the moon is actually 400 times smaller than that of the sun, but by an amazing coincidence, the moon is also 400 times closer to the earth, so it appears the same size in the sky as the sun. When it passes in front of the sun, it completely blocks the sun's light, casting a shadow on the earth that plunges everywhere it passes into darkness.
JASON KALIRAI: It requires this precise alignment between the earth, the moon and the sun. It doesn't happen all of the time, but, occasionally, we get lucky.
NARRATOR: If the moon were any closer to Earth, or any larger, it would obscure the object the scientists are trying to study: the sun's outer atmosphere, its corona.
JAY PASACHOFF: First contact, in other words, we can just look up, through a filter, and we see a bite out of the sun. And that's going to gradually grow bigger for the next hour and a quarter.
NARRATOR: To view this phase of the eclipse safely, it's essential to use specially designed solar filters. Although the moon is travelling in its orbit at over 2,000 miles an hour, it will take roughly 80 minutes before it completely covers the sun.
When that moment comes, known as second contact, it will be the start of the total eclipse.
But how do we know when and where a total solar eclipse will happen?
The last time one was visible from the continental United States was in February, 1979. Jimmy Carter was president, and the first personal computers were just going on sale. That was 38 years ago. But the gap between total eclipses can be much shorter.
ARCHIVE NEWSREEL: January 25th: Nature cooperating with ballyhoo. Elaborate preparations were made…
NARRATOR: In 1925, American astronomers watched a total eclipse as it passed from the middle of the country to the east coast. Some even flew in an airship to make observations.
This fortunate generation had already seen two total solar eclipses in the previous seven years and would see another only seven years later.
Despite this apparent randomness, there is a complex pattern behind eclipses, and, astonishingly, it was discovered over 2,000 years ago. Ancient Babylon, situated in what is now modern Iraq: for centuries, astronomers here kept meticulous records of their observations. They reveal that for Babylonian kings, eclipses were a matter of life and death. The British museum holds over 4,000 of these ancient astronomical texts.
MATHIEU OSSENDRIJVER (Humboldt University of Berlin): Whatever was seen in the sky was considered to be of relevance for the fate of the king, especially eclipses. They could announce war, they could announce his death.
NARRATOR: When an eclipse came, the king would stand down, and one of his subjects was appointed king in his place. But this new job came with a catch.
MATHIEU OSSENDRIJVER: Here, there is a letter in which the king asks, "How long is this fellow going to sit on the throne? When can I return?" And then the scholar replies: "Well, with the next full moon, he can go to his fate," meaning the substitute king would be killed, and the actual king would return to the throne, and the evil would have passed.
NARRATOR: To protect the king, astronomers had to be able to predict an eclipse. For hundreds of years they recorded every occasion an eclipse was reported. Eventually, around the 5th century B.C., they spotted a pattern.
MATHIEU OSSENDRIJVER: Some very clever Babylonian astronomers figured out that solar eclipses are governed by a cycle. This is the so-called Saros cycle.
NARRATOR: Today, we know that a total solar eclipse will take place, somewhere on Earth, about once every 18 months. But, with centuries of data, the Babylonians realized there was a larger pattern. Every 18 years, the time between eclipses would repeat.
MATHIEU OSSENDRIJVER: They could actually make an entire calendar of eclipse predictions simply by projecting these past eclipses into the future.
NARRATOR: Astonishingly, the Babylonian predictions were accurate to within an average of four hours, but they couldn't tell where in the world the eclipse would take place. It would take another 2,000 years before astronomers worked out how to do that.
At Harvard University, locked in the Houghton Library's special collection, is a rare document. It showed, for the first time, that the path of totality could be accurately predicted.
TYLER NORDGREN (University of Redlands): In 1715, the British astronomer Edmond Halley became the first person to correctly predict a total solar eclipse, by using the mathematics of his good friend, Isaac Newton, to calculate the orbit of the moon around the earth, and, therefore, where its shadow would fall across the countryside.
NARRATOR: In April of 1715, Halley published this map, forecasting that in two weeks' time an eclipse would pass over London. Halley had studied records of past eclipses, and rediscovered the Saros cycle, lost since ancient times. This told him an eclipse was due. He then used new, accurate observations of the moon's orbit to calculate its path.
Among the things he had to take into account was the unusual orbit of the moon, which is tilted by five degrees. So, most of the time, the moon's shadow misses our planet, which makes eclipses rare. He also had to factor in the gravitational effect of the earth and the sun, which subtly alters the moon's position.
By luck, Newton's new theory of gravity gave him just the tool he needed to accurately calculate the path of the eclipse across England.
TYLER NORDGREN: From comparing the maps that Edmond Halley made of the 1715 eclipse, both before and after, based on the observations by the public, we find that he was actually within about 20 miles, amazingly precise.
NARRATOR: And Halley's estimate of the time of the eclipse was off by just four minutes.
Today, with more accurate observations of the moon's orbit, astronomers can predict exactly where an eclipse will occur, and when, to the nearest second.
Six months before the eclipse over America, Jay Pasachoff has come to Argentina. He's here to witness another type of eclipse.
JAY PASACHOFF: I saw my first eclipse the beginning of my freshman year at Harvard. And it's just a thrill when the universe darkens around you. They're just so fascinating, I just want to see them all.
NARRATOR: For Jay, eclipses are a clear demonstration of the predictive power of modern science.
JAY PASACHOFF: The most remarkable thing is we've come half way around this side of the world—beautiful blue sky, perfect, normal conditions here—and yet, I confidently believe that in half an hour something is going to start going in front of the sun.
NARRATOR: Exactly as predicted, the moon starts its journey across the face of the sun. The filter on the camera darkens the sky, which is still bright. The eclipse Jay has come to see is not a total eclipse. It's called an "annular" eclipse, and it results from the shape of the moon's orbit.
The moon's orbit isn't a perfect circle; it's very slightly elliptical. So, when the moon is farther away from the earth, it appears smaller and doesn't completely cover the sun, creating an annular, or "ring of fire" eclipse.
JAY PASACHOFF: Look at the quality of the light. The color is a little eerie. It's clear that something strange is going on.
I see a bead.
NARRATOR: Even though the moon blocks out 99 percent of the sun's light, the experience for spectators, while still exciting, is different from a total eclipse.
JAY PASACHOFF: This is an annular eclipse. Here it's only going to get 100 times darker. So that's dramatic in some way, and it's fun to look at, but the total eclipse is the exciting one, where it really gets a million times darker in the middle of the day.
NARRATOR: Only the darkness of a total eclipse, like this one in Svalbard, Norway, enables scientists to see a part of the sun normally invisible: its outer atmosphere, the corona.
This elusive, pearly white cloud is made from a state of matter rarely found on Earth, called "plasma."
JASON KALIRAI: You know, every day in our lives we interact with solids, liquids and gases, but there's another one, and that's called plasma.
NARRATOR: If you heat a gas to a high enough temperature, some of the electrons in its atoms fly off, leaving positively charged ions. This superhot mixture of ions and electrons is known as a plasma.
JASON KALIRAI: It's an electrically charged gas. And, occasionally, we see examples of it, like lightning. Lightning is a plasma, and we can see it, but it's incredibly short-lived. In the corona, the natural state of matter is in a plasma.
NARRATOR: Although rare on Earth, plasma is the most common state of matter in the universe. Most stars we can see are made from it, including our sun. One-point-three-million times larger than the earth, our sun is a dense ball of plasma, made from hydrogen, helium and smaller amounts of other elements. The heat that creates this plasma is generated inside the sun, at the sun's core. Here, the extreme pressure of gravity forces the hydrogen atoms to fuse together, creating helium and releasing vast amounts of energy as photons of light.
This nuclear fusion heats the core to 27-million degrees Fahrenheit. From here, the photons of light pass through the dense inner layer of the sun. The temperature of the plasma gradually drops, as the photons reach the sun's visible surface, known as the "photosphere."
Here, rising and sinking plasma forms a seething surface of light and dark areas. Around the photosphere, is the corona, the sun's outer atmosphere of extremely diffuse plasma, extending far into space.
JASON KALIRAI: The word corona is a Latin word, meaning "crown." It's this crown around the sun, this beautiful halo. But it's not as dense as the sun, and so, ordinarily, we can't see it. Because the sun is so bright, we have to find a way to diminish the starlight, so we can see the details on its surface.
NARRATOR: A total eclipse does just that.
JASON KALIRAI: When the moon cancels out the disc of the sun, this beautiful halo is revealed, and we can then study that in detail.
NARRATOR: In Salem, Oregon, Jay Pasachoff's team is only minutes away from second contact, when the moon completely covers the sun.
JAY PASACHOFF: There's only one and a half minutes to go. There's only a very thin crescent now. Now, it's looking weirder. It just looks strange. It's hard to explain. You just know that something weird is happening.
It's just tremendously exciting to be outside when the universe darkens all around you, and that's a primeval thrill.
NARRATOR: As the moon closes over the last remaining crescent of the sun, tiny spots of light appear, like a string of beads.
JAY PASACHOFF: The English astronomer, Francis Baily, almost 200 years ago, saw bright little dots along the edge of the sun. And we now know that those are the everyday sun shining through the deepest valleys on the edge of the moon. And we call them Baily's Beads after their discoverer.
Fifteen seconds…five seconds…Baily's Beads…diamond ring…corona. Wow! Corona. Look at the shape there.
NARRATOR: The total eclipse has arrived.
CROWD EXCLAMATIONS OF AWE
JAY PASACHOFF: Look at that in the sky.
Whoa! Oh, my lord!
NARRATOR: Jay Pasachoff's team has just one minute and 55 seconds of darkness to photograph the corona.
JAY PASACHOFF: We can see it on the imaging. We've got a good exposure. We're looking at the corona here.
There's a big streamer coming down; two streamers going, going up, just beautiful.
NARRATOR: Jay's plan is to capture enough detail to reveal the structure of the corona. Because the brightness of the corona falls off the farther it is from the sun's surface, it's impossible to capture its detail in a single photograph. So, one of Jay's cameras takes a series of images at varying exposures, to capture the different parts of the corona. Combining these photographs reveals the corona is full of astonishing detail.
JAY PASACHOFF: Every time we look at the sun it's different. There are all kinds of streamers and little loops.
NARRATOR: The lines of plasma in the sun's corona are vast. They would dwarf the earth. The force that drives their shape and motion is the sun's magnetic field.
JAY PASACHOFF: We now know that those are the magnetic field of the sun holding this hot gas in place.
NARRATOR: We're familiar with magnetic fields on the earth; they give us our North and South Poles. But the sun also has magnetic fields, and they are far stronger.
As the sun turns, electrically charged plasma beneath the surface moves, generating powerful magnetic fields. Because the plasma is moving faster in some regions, it bends and twists these magnetic fields until some break through the sun's photosphere into the corona, where they form giant arches called "coronal loops." Because these magnetic fields trap electrically charged plasma, they show up as the bright lines and loops we see in the corona.
The sun's complex magnetic field, revealed during an eclipse, can directly affect us on Earth through a process called a "coronal mass ejection."
JASON KALIRAI: You can see these huge magnetic flux loops. And occasionally these magnetic flux loops can break.
NARRATOR: In a coronal mass ejection, the corona can throw over a billion tons of plasma out into space, at speeds of up to 2,000 miles per second. When a coronal mass ejection heads our way, the earth's magnetic field normally protects our planet; it deflects most of the highly charged particles. But a large coronal mass ejection can overwhelm our magnetic defenses with devastating consequences.
HOLLY GILBERT: These storms can impact our technology. They affect our satellites. They can cause power grids to go down.
NARRATOR: Powerful coronal mass ejections can cripple the power and communication systems our modern society relies on.
HOLLY GILBERT: When they impact the earth, they interact with the earth's magnetic field. They cause the magnetic field to bounce. Now this causes currents.
NARRATOR: As these currents surge through power lines, they can knock out transformers and, in an instant, put a city off-grid.
HOLLY GILBERT: We really want to be able to ultimately predict when these storms are going to occur.
NARRATOR: This group of scientists is on the front line of predicting a coronal mass ejection. From Boulder, Colorado, they use a fleet of satellites to monitor the sun 24/7.
The biggest event they ever saw happened in 2012.
BILL MURTAGH: And this is what we saw. All of a sudden, that flare occurs, the eruption occurs and that blast, it was tremendous—very big, very, very fast.
NARRATOR: If it had hit the earth it would have been a disaster, but fortunately it wasn't in the right place.
BILL MURTAGH: But, of course, the key is it has to be facing Earth for us to feel it. Near the middle of the sun there's a window we often refer to as the kill zone. When it occurs inside that zone, then it's Earth-directed, then we're going to feel the effects. Had it occurred a week earlier, the impact would have been here on Earth, and it could have been very significant.
NARRATOR: A large storm like this very rarely hits our planet, but in the last 40 years, smaller storms have damaged or disabled over a dozen satellites. And in 1989, one knocked out the power supply to the Canadian province of Quebec.
To minimize the risk of devastating damage, Bill and the team must predict when a powerful coronal mass ejection will strike.
BILL MURTAGH: We would love to improve our capability to predict. If we can better model what the magnetic field might look like within the eruption, then we'd be in a great place.
NARRATOR: And a total solar eclipse is essential to this effort.
Twenty five minutes after the eclipse reached Salem, Oregon, it arrives at Casper Mountain, in Wyoming.
Here, at 8,000 feet, scientist Steve Tomczyk is setting up an experiment to see how these coronal mass ejections are created by the sun's magnetic field.
STEVE TOMCZYK: Well, we're trying to find out how the corona is oriented, and that's important because energy is stored in the coronal magnetic fields.
NARRATOR: Steve hopes his new camera will help him understand these magnetic fields.
STEVE TOMCZYK: So, magnetism is very important in controlling the plasma and causing the plasma to erupt in coronal mass ejections.
NARRATOR: It's magnetism that triggers these violent events. The corona contains highly charged plasma trapped in magnetic fields. When these magnetic fields become twisted, they can rise up, stretching other magnetic fields, until they suddenly snap and reconnect, releasing huge amounts of energy as the plasma blasts into space as a coronal mass ejection.
STEVE TOMCZYK: You can remove them.
NARRATOR: This is where the new camera helps. It will reveal evidence of the twisted magnetic fields, which are a sign that a coronal mass ejection is about to erupt.
STEVE TOMCZYK: This camera allows us to measure the polarization in the corona, over the entire corona, and allows us to possibly, eventually, predict when coronal mass ejections will occur.
NARRATOR: To the west of Casper Mountain, the moon's shadow races across the plains at over 1,600 miles an hour. The eclipse is moments away.
As the sky darkens, the air begins to chill. During a total solar eclipse, the temperature can drop as much as 28 degrees.
Moments later, the total eclipse reaches Casper Mountain.
NARRATOR: Steve's gamble has paid off. The conditions are perfect to carry out his observations.
STEVE TOMCZYK: C3 plus 40 is flashed, so I think we're done. And we're starting to saturate, so I think we're good. You can cover the flash now.
NARRATOR: Here at Casper Mountain, totality lasts only two minutes and 26 seconds.
But is there a way to extend the viewing time?
Ellington Airfield, Houston, Texas; 8 a.m.: A NASA crew prepares an audacious mission to view the eclipse for three times longer than anywhere on the ground. Their plan is to use telescopes attached to the nosecones of two WB-57 jets, to track the sun and record video of the corona.
Amir Caspi is the scientist in charge.
AMIR CASPI: At about 50,000 feet, we're going to be above 85 to 90 percent of the atmosphere, which will make our image quality much better than it would be than if we were on the ground.
NARRATOR: From Houston, the two NASA jets fly to Southern Illinois, where they will line up 50 miles apart and fly along the eclipse path.
As the moon's shadow races over the jets, they will observe the eclipse, one after the other.
AMIR CASPI: And the idea is that they pick up the track and follow the track straight through.
NARRATOR: The jets aren't fast enough to keep up with the eclipse shadow—travelling around 1,600 miles an hour—nearly three times as fast as the planes. By flying two jets, Amir hopes to extend the viewing time to over seven minutes.
AMIR CASPI: By having two airplanes, we can stage them in such a way that, when the shadow finishes passing over that airplane, it starts passing over the second airplane. And so then we can put those two data sets together and get a longer observation.
NARRATOR: Amir and the team are trying to solve a mystery that has baffled scientists for decades. In the late 1800s, an American astronomer, studying the corona during an eclipse, made an astonishing discovery.
TYLER NORDGREN: In 1869, there was a total solar eclipse visible from the United States, and Charles Young, an astronomer at Dartmouth College, led an expedition to Iowa in order to use the brand new technology of spectroscopy.
NARRATOR: A spectroscope uses a prism to divide white light into its constituent colors, or wavelengths. If you heat an element strongly enough, its gas emits light in very specific wavelengths. Viewed through a spectroscope, each element has its own unique pattern of colored lines. By pointing a spectroscope at the corona during an eclipse, Young hoped to find the elements it contained. What he discovered was a mysterious spectral line no one had ever seen coming from any element on Earth.
TYLER NORDGREN: He noticed there was a special green line, green light emitted from the corona. And since it matched up with no known element, people naturally assumed that there must be some new element, not existing here on the earth or hadn't been discovered.
NARRATOR: Scientists gave this strange new element a name, "coronium," because it had been discovered in the corona.
TYLER NORDGREN: For the next 70 years, astronomers sought to identify what this mystery element might be. What they found, in fact, was that it was a known element: iron—iron at such a high temperature that 13 of its 26 electrons had been ripped away.
NARRATOR: Astonishingly, the corona was so hot, it had turned the metal iron into a plasma with a spectral line completely different from iron found on Earth.
TYLER NORDGREN: Only under extraordinarily high temperatures is this ever possible. So, when you see a total solar eclipse and you witness that amazing corona, you are seeing an object at a million degrees. It is the hottest thing you will ever see with the human eye.
NARRATOR: And that's the problem. The surface of the sun is only about 10,000 degrees Fahrenheit. How can the sun's outer atmosphere be hotter than its surface? It seems to defy the basic laws of physics.
HOLLY GILBERT: The energy in the sun is being generated at its core, in the center. Now, as you move away from the core, you expect things to get cooler, you're moving away from the source of the energy.
Same thing, as I'm sitting here close to the fire, it's hot. If I were to move away, it would get cooler and cooler.
And that does happen, up until the surface of the sun, but then all of a sudden, as you move farther away from the surface, it gets really hot again. We do not understand what is causing this extreme change in temperature.
NARRATOR: So what is heating the corona?
AMIR CASPI: One of the leading theories is this theory of "nanoflares," which are small, what we call "impulsive" events. They happen very quickly.
NARRATOR: Nanoflares are thought to be explosions on the sun that are too small to be seen directly by ground-based telescopes, but there is evidence they exist.
Recently, at the White Sands Missile Range, in New Mexico, this group of scientists launched a research rocket into space to study nanoflares.
DON HASSLER (Southwest Research Institute): I've been launching rockets for 30 years. When you fly a satellite program, you spend weeks aligning it, focusing it, calibrating it. The biggest challenge with rockets is it's only a five minute flight, so it has to work right when you open the door.
NARRATOR: On board is a modern electronic version of Young's spectroscope. It will briefly photograph the sun, before the rocket falls back to Earth.
DON HASSLER: We spend years developing the instrument, but actually seeing it work and fly it in space, is really the icing on the cake.
NARRATOR: The advanced spectrograph is designed to analyze the light from brief flashes of extremely hot plasma, the signature of nanoflares.
According to the theory, the trigger for nanoflares comes from the sun's magnetic fields.
JIM KLIMCHUK (NASA's Goddard Space Flight Center): Like most interesting phenomena on the sun, they involve magnetic fields in a fundamental way. So these fields are much, in fact, like rubber bands. They can be stretched and twisted and stressed, and eventually they reach a breaking point. And when they do, they snap.
NARRATOR: The arches of plasma that rise from the sun's surface can be made up of many magnetic field lines. As the sun's plasma churns at the surface, it can twist and tangle these magnetic field lines, creating stresses that build up, until eventually the lines break and reconnect in a simpler configuration. This releases huge amounts of energy in a nanoflare.
Millions of nanoflares are thought to be going off each second, beginning at the sun's surface and reaching into the corona, to heat it to over a million degrees.
JIM KLIMCHUK: Each nanoflare is the equivalent of a 50 megaton hydrogen bomb. They're happening at a tremendous rate—a million or so per second—across the sun, so collectively, they really pack a wallop.
NARRATOR: At White Sands, the spectrograph designed to find nanoflares will soar 200 miles above the earth.
VOICE ON PA: Fifty seconds and counting.
NARRATOR: The rocket will take it beyond the earth's atmosphere, which would absorb the light they are trying to detect.
BRITTANY MCKINLAY (Mission Manager, Orbital ATK): All stations, this is MM calling for go status. Navy?
NAVY: Okay to go.
BRITTANY MCKINLAY: T.M?
ADAM BLAKE: T.M. is go.
BRITTANY MCKINLAY: S.I.D?
S.I.D.: We're go.
LUPE ARCGULETA: 10, 9, 8, 7, 6, 5, 4, 3, 2, 1: liftoff.
DON HASSLER: Come on. Second stage. Yes!
NARRATOR: After five minutes in space, the spectrograph lands safely. The mission is a success.
DON HASSLER: Outstanding.
NARRATOR: It will take the team months to process the results…
DON HASSLER: So, we have any broken?
NARRATOR: but the first indication that nanoflares really do exist came from a flight like this in 2013.
That rocket captured images that indicate a surprisingly hot plasma.
JIM KLIMCHUK: The emission that we see here indicates very, very hot plasma.
It's a very faint emission, and we, in fact, expect it to be very faint. But it's there, and that is the smoking gun of nanoflares.
NARRATOR: Spectral lines provided evidence of iron stripped of 18 electrons, and that can only happen at 16 million degrees hotter than even the corona, and a temperature that it's thought only nanoflares can produce.
So far, signs of nanoflares have been found only near the sun's surface, but, during the eclipse, Amir's team will use its planes to look for nanoflares thousands of miles above the surface, in the corona.
AMIR CASPI: We don't know where they might be occurring. There could be nanoflares occurring higher up in the corona. Because we can't see them, we can only see the results of these nanoflares, it's hard to know. And that's one of the things that we hope to learn from this eclipse observation.
NARRATOR: In Houston, Amir Caspi anxiously awaits the live feed from the telescopes on the NASA jets.
AMIR CASPI: I'm not sure what's going on. Two minutes to eclipse. Planes are in position, although the live streams are a little flaky. Right now, the first plane, the westward plane should be in the path of totality. It should be experiencing a total solar eclipse. Unfortunately, we don't have the live video feed right now.
NARRATOR: Just then the video feed comes in.
AMIR CASPI: That looks great. That is beautiful, that is beautiful.
We got observations. We got totality so…had a little bit of a touch and go with the live feed there, but we got some great observations. I'm pumped. See that streamer coming out of here?
NARRATOR: The operation is a success.
AMIR CASPI: Until we get the scientific quality data on the ground, we won't know for sure if we saw what we were hoping to see. On the other hand, whatever we see is going to be interesting. It's going to teach us about how energy gets from the center of the sun out to the solar corona, how it heats the solar corona. It'll take a little while to extract all of that information, but we got what we came for.
NARRATOR: While the darkness of totality, with its view of the corona, is great for science, for sheer spectacle it's hard to beat the end of a total eclipse.
The last moment of totality is called third contact, the moment when the moon starts to reveal the sun's light again. As soon as this happens, the sun creates a brief, but dazzling spectacle. When the first rays of sunlight reappear, they sparkle like a brilliant jewel.
Since the 1920s, this moment of the eclipse, the glowing circle of the corona welded to a bright spot of light, has been known as the Diamond Ring. The name comes from the eclipse that passed over the east coast in January, 1925.
From New York to Washington, D.C., people flocked to see it. President Coolidge watched it from the White House.
TYLER NORDGREN: One of the things they reported was a diamond ring: a bright point of light set in this diaphanous circle of corona. And so it's come down to us today, this term, which I still find to be one of the most beautiful sights to see during a total solar eclipse.
NARRATOR: Salem, Oregon: at 10:19 local time, the moon moved away from the edge of the sun, revealing the diamond ring.
CROWD CHEERS AND APPLAUDS
NARRATOR: It's the end of totality.
JAY PASACHOFF: Just gorgeous. Congratulations, everybody.
NARRATOR: For the scientists, it's time to check their observations of the corona.
JAY PASACHOFF: Today's view of the sun will be one of the best ever, in history. It's such an amazing experience.
NARRATOR: Jay has the first images from the eclipse, but he won't be able to see the details in the corona until he has processed the data.
JAY PASACHOFF: We had predictions based on what the corona might look like, and now we'll go back and compare what it actually did look like, and prove the theory. So we'll be analyzing that for a long time.
NARRATOR: On Casper Mountain, the moon's shadow passes on its way, throwing the land into light again. The diamond ring appears, and the total eclipse is over.
STEVE TOMCZYK: Interesting, really interesting.
NARRATOR: It's the moment of truth for Steve Tomczyk. Did the new camera work?
STEVE TOMCZYK: The data look really good. We're going to have a lot of fun the next few months analyzing the data. Really exciting, very exciting.
Good job everybody, fabulous. High fives.
NARRATOR: It's another small step towards understanding the forces that trigger coronal mass ejections.
The 2017 total solar eclipse was the first to cross the United States from coast to coast in nearly a hundred years. Its path, over several major cities, meant that millions of people were able to experience this unique spectacle.
CROWD COMMENTS: This is the coolest thing I've ever seen. It's awesome.
It's spiritual. It's emotional.
When I watched it, my jaw was completely open.
There are scientists here, there are people from all over the world, different languages being spoken. And I think we've all just united by this amazing kind of cosmic event that reminds us where we are in the universe.
NARRATOR: For 90 minutes today, the eclipse transfixed the nation. And, if you missed it, in less than seven years, another total solar eclipse will cross America, once again reminding us of our special connection with our nearest star, the sun.
PRODUCED AND DIRECTED BY Martin Gorst EXECUTIVE PRODUCERS Chris Schmidt
Carlo Massarella EDITED BY Paul Shepard DAY-OF PRODUCERS Michael H. Amundson
Robert Tinworth SPECIAL PHOTOGRAPHY Ron Dantowitz LOCATION DIRECTORS David Dugan
Matthew Ainsworth LOCATION SHOOTER Jason Longo NARRATED BY Craig Sechler GRAPHICS Darkside Studios ASSISTANT PRODUCER Sacha Thorpe SENIOR RESEARCHER Maia Krall-Fry PRODUCTION MANAGERS Viki Carter
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Michael Tivey SATELLITE ENGINEERS Joe Pugliesi
Dan Brown ARCHIVAL MATERIAL Alex Cherney
Miloslav Druckmüller, Peter Aniol, Martin Dietzel, Vojtech Rušin
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A NOVA Production by Windfall Films Ltd. (part of the Argonon Group) for WGBH Boston produced in association with NHK, Canal+ and N24.
© 2017 WGBH Educational Foundation
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This program was produced by WGBH, which is solely responsible for its content.
Original funding for this program was provided by Draper, 23andMe, the David H. Koch Fund for Science, The Neil & Anna Rasmussen Foundation and the Corporation for Public Broadcasting.
IMAGE: Image credit (Moon between NASA’s Solar Dynamics Observatory and the Sun) Courtesy NASA/SDO