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00:00The sun, our nuclear powerhouse, our star, its light powers our world and us.
00:16Without light, we would not be alive.
00:23Starting deep inside the sun, we follow the brutal journey of a single tiny package of light, a photon.
00:33The ride that any photon takes to get to my eyes when I look up at the sun is amazing.
00:38From its ancient birth in the sun's core to its escape from the surface.
00:46The light reaching me from the sun was produced before there was even human civilization.
00:51It's an incredible idea.
00:54Join our photon on its incredible million-year journey through the most hostile environment in the solar system
01:03to bring light and life to Earth.
01:16The universe, home to billions of galaxies, each made of billions of stars.
01:37And in an unremarkable corner of our galaxy, the Milky Way, lies the sun, our closest star.
01:48A dazzling sphere of intense light, too bright for the naked eye.
01:56Strip away that glare and the sun transforms into a giant ball of superheated gas, dominating our cosmic stage.
02:11The sun is really the star of the show.
02:13The sun is the parent of the whole solar system.
02:18It provides its children, the planets, with everything they need.
02:22We depend on the sun for energy, for light, for warmth.
02:26We would not exist without the sun.
02:32The sun generates heat and light, the energy source for all life on Earth.
02:39All of the energy that my body uses, literally what I'm doing to talk to you right now, came from the sun.
02:45The sun truly is the creator of all of the life around us.
02:50The sun is a constantly exploding nuclear bomb, violent and essential.
02:59Our entire existence is powered by the energy emitted in those nuclear reactions of the sun.
03:05We are here because of the light from the sun.
03:08We are here because of those nuclear reactions.
03:10And no aspect of our existence could persist if it wasn't there.
03:17Light is one of the basic building blocks of the universe.
03:27I find light to be probably the most amazing thing in the universe.
03:31It's so important in everything. I mean, it's everything. It's everywhere.
03:35So it's such a fundamental part of everything that exists.
03:40Fundamental and fast.
03:44The fastest thing in the cosmos.
03:47Traveling at 186,000 miles per second.
03:54The sun's about 93 million miles away from us.
03:57So going at 186,000 miles per second, that's about eight minutes.
04:01But those eight minutes are just the brief last leg of its incredible journey.
04:12It may have taken the light as much as a million years to escape from the sun's raging interior.
04:20Which means the light we're seeing right now was created long before our ancestors left the plains of Africa.
04:32When I first learned this fact, I was already a practicing scientist.
04:35I'd never really thought about that.
04:37And on first glance, it just blew me away.
04:40Right now, the light reaching me from the sun was produced before there was even human civilization.
04:45And yet the minute it gets to the surface of the sun, it races away and is here eight minutes after that.
04:50It's an incredible idea.
04:53The ride that any photon takes to get to my eyes when I look up at the sun is an amazing one.
05:02That ride starts deep in the belly of our star.
05:07If we could open up the sun, we'd see layers of dense hydrogen gas hundreds of thousands of miles deep.
05:17And at its center, the core, the sun gives birth to light.
05:26Forged in one of the most violent reactions in the universe.
05:31Nuclear fusion.
05:39The specific nuclear reaction that powers the sun is fusion.
05:42Fusion of hydrogen into helium.
05:44You take two hydrogen atoms, you ram them together, and what's left over is a helium atom.
05:49It sounds exciting enough, but it's not.
05:53It's actually hard to get two atoms to fuse.
05:56Photons have the same charge.
05:57They're both positively charged.
05:59They want to repel each other.
06:03Photons don't like to get close together.
06:05They have to come together with a huge amount of energy or velocity to get close enough to begin to fuse, and that's very, very rare.
06:15To force photons together takes immense amounts of heat and pressure.
06:23Generated by the invisible act of gravity, the sun contains 99.8% of all the matter in the solar system.
06:34That's a lot of mass.
06:36All that mass pulls the sun together with unimaginable gravitational force.
06:45With gravity crushing things down, things get close enough together, and nuclear fusion happens.
06:51In this nuclear compactor, hydrogen atoms slam together 100 million quadrillion quadrillion times each second.
07:05Some of these collisions are so powerful that atoms fuse, releasing energy.
07:12When the protons come together, they bind together, they lose a little bit of mass, and that mass gets converted into energy.
07:20And every second of every day, about 5 million tons of stuff is being converted to energy.
07:29It's amazing.
07:36Each collision creates a tiny burst of energy, a packet of light, impossibly small and incredibly powerful, a photon.
07:48Somehow, our photon will deliver its energy to Earth, where it will power the planet and make life possible.
07:57But right now, it's nothing like the light we see.
08:02It has massive amounts of energy and is deadly.
08:19The light we see from our star is old.
08:24It's much older than the eight minutes it takes to get from the sun to Earth.
08:30That short leap across space is the end of a long, hard journey that starts deep inside our sun.
08:38When we look at the sun, we say, how beautiful, how elegant, and how simple.
08:43Light is formed in the sun, and it shines and lights up our world.
08:47Well, not so fast. It's actually very complex.
08:54The journey starts in the immense heat of the sun's core.
09:03Crushed together by the sun's enormous gravity, atoms smash into each other and fuse,
09:11releasing a tiny packet of energy, a photon of light.
09:18Far smaller than an atom and with no mass, photons travel faster than anything else, and they never stop moving.
09:35Photons don't just come from the core of stars.
09:40So where does light come from? The short answer is, matter makes it.
09:45And the amount of light that it creates depends on its temperature.
09:50Every piece of matter in the universe above absolute zero degrees produces light, including humans.
09:59We humans are emitting light all the time because we're alive, we're warm, we're not at a zero temperature.
10:05So in fact, we are emitting infrared radiation, often called heat radiation.
10:10But all matter emits light.
10:12Even someone as cool as me, I'm creating light right now.
10:19The light we see can be split into the colors of the rainbow.
10:24Each color is photons of light with slightly different amounts of energy.
10:32And what we can see is only a fraction of the light spectrum.
10:38Our eyes are actually imperfect detectors.
10:40We know about visible light, the type of light that our eyes are sensitive to, but that's only a small range of energies.
10:46Light comes at higher and lower energies than we can detect.
10:51Using special cameras, we can see the infrared light that humans emit.
10:59This infrared light has less energy than the visible light we normally see.
11:07Ultraviolet light, X-rays, and gamma rays are too energetic to see.
11:19The vast, hot sun generates all forms of light.
11:25But in the nuclear furnace of the sun's core, every photon starts out as a gamma ray, the most energetic form of light in the universe.
11:37And when a nuclear reaction happens, it emits an amazing amount of energy, energy much, much bigger than visible light.
11:43Gamma rays become literally almost a million times or at least 10,000 times the energy of the light we see.
11:52Gamma rays can transform and even kill.
11:57There's a reason why gamma rays turn Bruce Banner into the Hulk.
12:01Gamma rays are a very dangerous form of light.
12:04They can travel into your body, and when they interact with the matter, they can break apart atoms.
12:09Fortunately for us, our gamma ray photon can't hit straight out at the sun.
12:17If the sun were not this hot ball of gas, then upon being created, a photon would immediately escape from the sun,
12:31and it would be a gamma ray photon, a very energetic photon, not very good for life on Earth.
12:38After its birth as a gamma ray, our photon starts to race out from the sun's core at the speed of light.
12:49But it encounters an obstacle course of epic proportions.
12:54A journey that should take seconds slows to a cosmic crawl.
13:01It takes, on average, about 100,000 years for a photon to make it from the middle of the sun where it was created
13:11to the outermost edge where it gets emitted into space.
13:14100,000 years. If it had traveled in a straight line unimpeded, it would have taken two seconds.
13:21What could possibly slow the journey of a photon moving at the speed of light?
13:28Something slams the brakes on.
13:32Huge. Hot. Dense. So powerful, it doesn't just slow light, it transforms it.
13:57In the sun's core, nuclear fusion releases a tiny bundle of energy, a photon of light.
14:09It races outward at 186,000 miles per second.
14:17At that speed, it should take two seconds to travel through the sun's interior to the surface.
14:25But something turns seconds into an eternity.
14:31The sun is so dense that to get through all of the different layers of gas,
14:35this poor little piece of light takes hundreds of thousands if not a million years to get to the surface.
14:44So when you're looking at the sun, you're looking at the light emitted from reactions a million years ago.
14:51Our newborn photon leaves the core at the speed of light only to run smack into a dense center of hydrogen atoms,
15:00a photon's nightmare that stretches for over 400,000 miles.
15:06If you're a photon born in the center of the sun, you have a heck of a journey ahead of you.
15:11It's actually pretty hard for light generated in the core of the sun to get out
15:15because there's a lot of sun in the way and it's extremely dense.
15:21The radiation zone surrounds the core of the sun.
15:26This zone is made of hydrogen gas, but not a gas as we think of it.
15:34The sheer weight of all the material above compresses the radiation zone
15:40until it's denser than lead and nearly impossible to pass through.
15:46A photon produced in the center of the sun knows where it wants to go.
15:51It wants to go to the edge where it's cool and it wants to get out.
15:56But it's got 400,000 miles of all these opaque gases blocking its way.
16:04These gases aren't just dense, they're hot, superheated to over 12.5 million degrees Fahrenheit.
16:12The gas in the radiation zone is transformed into what scientists call plasma.
16:22Plasma is the fourth state of matter.
16:25Atoms in normal matter have a nucleus with orbiting electrons.
16:29In plasma, the atoms have been torn apart and the electrons ripped away.
16:35Here on Earth, we're familiar with the three main states of matter that we're taught in school.
16:40Solids, liquids, and gases.
16:43You know, we have the atmosphere as a gas, the oceans are water, the ground that I stand on is solid.
16:48But in fact, most of the universe, including stars, consists of plasma.
16:56Compared to the rest of the universe, Earth is a mass of matter.
17:02Compared to the rest of the universe, Earth is a calm place.
17:07Most of the time, it's not hot or violent enough to create plasma.
17:17The best place to witness the power of plasma on Earth is inside a lightning strike.
17:24Temperatures inside a bolt can reach 53,000 degrees Fahrenheit,
17:30enough to momentarily rip a few atoms apart.
17:37The plasma lasts an instant, then the electrons rebind and it's gone.
17:46But in our massive sun, the plasma lasts for billions of years
17:52and makes up the entire 200,000 mile deep radiation zone.
18:00Worse for a photon, the plasma is electrically charged, forming a cosmic ray.
18:12And a plasma is opaque to radiation because light interacts much more strongly
18:18with electronically charged objects than with neutral objects.
18:21So when you have a neutral atom, light in general can pass by.
18:25But when you've separated the charges and you have positive and negative charges located everywhere,
18:29the light can't make it through.
18:32Our photon, in the form of a gamma ray, has entered the radiation zone
18:37and smashed into a charged plasma particle.
18:41For a fraction of a second, the particle absorbs the photon,
18:45then spits it back out and the photon collides with another particle.
18:54Every time it goes a little bit of a distance, it basically slams into an atom,
18:58is absorbed and re-emitted in some random direction.
19:01So instead of just flying out, it's bouncing around countless, countless, countless times
19:06until finally it reaches the edge of the star.
19:10It's an atomic game of basketball, with a court representing the radiation zone.
19:16The players stand in for the particles in the plasma, and the ball is the photon.
19:26So the basketball is being thrown from one player to another, seemingly randomly.
19:31It's not making a lot of progress down the court.
19:34But it is gradually making progress.
19:37Gradually over time, it is flying from the hotter parts of the core
19:41outward toward cooler temperatures.
19:44That's where it wants to get.
19:46It's a random-looking process, but it's directed in a certain direction with time.
19:57The photon wants to go straight up court, the quickest route.
20:02But it's bounced and thrown around the radiation zone, slowing progress to a crawl.
20:09This bruising process transforms the photon.
20:14When a photon, a little packet of light, is created in the center of the star,
20:18it's actually a gamma-ray, super high-energy bit of light.
20:22And it can't go very far, because as soon as it does, boom, it hits another atom.
20:26It gets absorbed.
20:29Every time it does this, it loses a little bit of that energy.
20:34Over several hundred thousand years, sometimes even a million,
20:39the photon keeps bouncing through the dense radiation zone.
20:45Each collision saps a tiny bit of energy,
20:50transforming it from a lethal gamma-ray photon to a lower-energy X-ray.
20:59Nearly a million years after its creation in the core,
21:03the photon has made it through the radiation zone.
21:08But its quest to escape is not over yet.
21:13It's about to hitch a wild ride on the sun's ferocious internal rollercoaster,
21:19a place so violent it makes the sun roar.
21:29NASA Jet Propulsion Laboratory, California Institute of Technology
21:45A photon, nature's energy delivery system,
21:49has spent up to a million years in the maze of the sun's interior,
21:53on its journey toward Earth.
21:57The photon has fought its way through three-quarters of the sun's radius.
22:03Battered and sapped of energy, it has morphed from a deadly gamma-ray to an X-ray.
22:12But it now enters the mysterious boiling lake of the sun,
22:17the convection zone.
22:21The convection zone lies between the radiation zone and the sun's surface,
22:27and is 125,000 miles deep.
22:33We can't see the convection zone directly.
22:37This region of the sun is still opaque to our telescopes.
22:42But we can hear it.
22:47NASA's Solar Dynamics Observatory listens to the sun.
22:54The sound it picks up is too deep for humans to hear.
22:59But if you speed up 40 days' recording into a few seconds, this is what you get.
23:10This is the sound of chaos.
23:17Since we can't see into the sun, its sound is vital to scientists.
23:25When a gun fires, the bullet rushes out and smashes into air, creating waves of turbulence.
23:36We hear the gun firing when these waves vibrate our eardrums.
23:43What we can see here is sound.
23:48The sun works the same way on a much larger scale.
23:56When we see these waves moving across, what we're looking at is when material moves up from inside the sun and it makes noise.
24:04It's just like it ran into a surface, it just ran into a wall, and it generates sound,
24:09and we see that sound moving all around the sun.
24:13Sound waves crashing through the plasma create ripples in the sun's surface.
24:19And all we see are these ripples. Those are the actual sound waves of the sun.
24:24And they move around the entire sun, they move down inside the sun, they move back up to the surface.
24:32By tracking the sound, scientists can see the invisible.
24:39They pick up sound waves smashing against the sun's surface and resonating throughout the solar interior,
24:47revealing a violent, boiling convection zone.
24:55The sun can be said to be ringing.
24:59You have this hot gas rising, you have cool gas falling, you have all this turbulence,
25:05you have so much action going on that it causes the sun to ring.
25:10Columns of gases rise and fall, churned by heat from below.
25:18If you look at water boiling, bubbles of gas or water are rising up because they're hot,
25:23and then they cool off and then they sink back down.
25:26And if you look at a pot of boiling water, that's the same phenomena that's going on on the sun,
25:31but with hot plasma instead of water.
25:35At the bottom of the convection zone, photons smash into atoms in the plasma, heating them to a boil.
25:44But this time the photons are absorbed by the atoms and drive the boiling current to the top.
25:51The hot atoms drag the photons with them.
25:58So it's almost like this conveyor belt of material.
26:01Photons are actually hitchhiking a ride on the atoms that are traveling upward through this heat transfer.
26:07So it's a much easier ride in the convection layer than it is in the radiation zone.
26:16It's as if our photon were now in the hands of a single player, making a fast break.
26:24In the convection layer, it's a direct path.
26:29One player can actually hold on to this basketball or photon for a lot longer in a direct path.
26:37By not passing, the atom takes the ball quickly off court.
26:44The photon's journey through the convection zone takes just a week.
26:50But in that time, it transforms the photon.
26:54The bottom of the convection zone is around 360,000 degrees Fahrenheit.
27:02The top, just 10,000 degrees.
27:07So as the photon rises up, it cools, losing energy, changing from an energetic x-ray to visible light.
27:17So it starts as a high-energy x-ray at the bottom of the convection zone, moves its way up, and loses a little bit of that energy.
27:25By the time it leaves there, it's closer to the kind of light that we see, which is visible light.
27:34At the top of the convection zone, the atom releases the photon, which shoots out as visible light.
27:41This cools the atoms, which fall back down to absorb more photons, heat up, and rise again.
27:51The photon is now just below the sun's surface.
27:55But the churning convection zone unleashes another force.
28:00A force that powers huge storms, detonates bombs, and threatens life.
28:06A force that powers huge storms, detonates bombs, and threatens to stop life's escape.
28:13A force that powers huge storms, detonates bombs, and threatens to stop life's escape.
28:33In the sun's core, nuclear fusion has created a photon, a pack of light.
28:39It has battled through the radiation zone.
28:43And dragged up through the convection zone on columns of hot plasma, hurtling towards its escape.
28:53On this million-year journey, the photon has changed from an invisible deadly gamma ray to the kind of life-giving light we see here on Earth.
29:04Finally, it has reached the surface, the visible shell of the sun, the photosphere.
29:20The photosphere, which is basically the visible part of the sun, or the surface, is what we see when we look up at the sun.
29:27We're seeing visible light coming from that very layer, the photosphere.
29:35The ball of blinding light we perceive hides a spectacular and sad world.
29:45The sun from a distance looks quiet and serene.
29:49But if you take a close-up of the surface of the sun, you see that it's churning with activity.
29:57It's beautiful and terrifying at the same time.
30:00Huge storms of material bubbling and boiling.
30:03It looks like a witch's brew, except the bubbles in the witch's brew are larger than the size of the Earth.
30:11The surface of the sun is a turbulent barrier.
30:16And once again, our photon gets taken hostage.
30:31At Kitt Peak Observatory in Arizona, solar astronomer Matt Penn studies this solar surface to discover how photons of light get trapped.
30:50Using the McNath-Pierce telescope, he focuses the sun's light to scan the photosphere in detail.
30:57So what we've got are a few small sunspots on the disk of the sun.
31:01We've got two sunspots, two large ones.
31:04They're heading off to the edge of the sun, to the limb of the sun.
31:07But they're all accompanied by smaller sunspots, groups of smaller ones following them.
31:14Sunspots mark out areas where light is trapped.
31:20So a sunspot forms a dark spot by removing energy from that part of the sun.
31:24It's blocking the convective flows that transport the heat and the light from inside the sun to space.
31:29And so what we see then is a cooler region that appears dark to us.
31:35A powerful force stops our photon dead in its tracks, preventing its light and energy from leaving the sun's surface.
31:46That force is magnetism.
31:50Sunspots take shape where intense magnetism from deep inside the sun blasts up through the photosphere.
32:02The magnetic field is so strong that it actually stops the convective motion of hot inner material from flowing to the surface.
32:11So you actually get what looks like a cool region of the sun.
32:14They can be huge, the largest over ten times the size of the earth.
32:26The magnetism that generates these sunspots forms field lines covering the sun.
32:33On our solid earth, the whole planet is a magnet.
32:37But the sun is a big ball of gas, and the same rules don't apply.
32:42You see, there's nothing solid about the sun. It's a big ball of gas.
32:46It turns on its axis, but the equator rotates faster than the poles.
32:50The sun twists itself up, and the magnetic field twists with it.
32:54The magnetic field is so strong that it actually stops the convective motion of hot inner material from flowing to the surface.
33:03The sun twists itself up, and the magnetic field twists with it.
33:08It rotates faster at the equator than at the poles, twisting and tangling its magnetic field with each rotation.
33:19The result is magnetic mayhem.
33:23So when these fields emerge from the surface of the sun, they have all this stored energy in them.
33:29They're like all twisted and knotted, like a rubber band is just twisted and knotted.
33:33With all this energy in it, if you ever twist and twist and twist a rubber band and pull it straight,
33:37you can tell, you can feel that tension.
33:42Where the magnetic lines twist, flows of plasma containing our photon can't go anywhere.
33:49Where the plasma containing our photon can't reach the surface.
33:54So what happens is you have these packets of gas which reach the surface, cool off, but are trapped right there by the magnetism.
34:05A patch of the sun goes dark where light can't escape. A sunspot is born.
34:13But in that tangle of magnetic lines, something eventually has to snap.
34:19The magnetic fields are very unhappy. They don't like the state that they're in, and all they want to do is unravel.
34:30Huge loops of magnetic energy arc out over the sunspots.
34:38Twisted and unstable, desperate to spew their energy, they create a magnetic bomb, prompted to explode.
34:49And so if one magnetic field with stored energy sees another magnetic field,
34:54those two look at each other and say, hey, if we connect, we get rid of a lot of energy.
34:58They do so. They reconnect. Wow!
35:11It's a huge explosion. We call it a solar flare.
35:15And this can be equivalent to millions of nuclear weapons exploding simultaneously.
35:25Solar flares erupt outwards into space at up to four and a half million miles an hour, releasing massive amounts of energy.
35:37Magnetic fields are throwing plasma from the surface of the sun. Suddenly, there's a large outpouring of light.
35:48After nearly a million years, our packet of light escapes.
35:57It is finally free, catapulting out along with trillions of other photons.
36:07But their journey is far from over.
36:12Most hurtle onwards to the far reaches of the cosmos, to strange new worlds.
36:20NASA Jet Propulsion Laboratory, California Institute of Technology
36:32After a nearly million-year journey through the most hostile environment in the solar system,
36:40tiny packets of light, photons, finally burst from the sun's surface.
36:50They're free. They basically are free to leave this arduous journey that they've been on during the sun,
36:57and then they fly out at the speed of light.
37:02So it's kind of a breaking out of prison type of feeling for those poor photons.
37:09They speed out into empty space at 186,000 miles per second,
37:15and just 8.3 minutes after it leaves the sun, our photon reaches Earth.
37:22The next time you look at a star in the sky, you might consider the amazing journey the photons have taken on their way to reaching your eye.
37:33They were created by nuclear reactions deep in the core of the stars,
37:38and then they bounced around and got degraded into lower energy photons.
37:43And then in the convective zone, they were carried by mass motions of gas.
37:49And finally, at the edge, they were set free.
37:55And they traveled unimpeded and finally reached your eyes.
38:00Our photon finally arrives, smashes into a leaf, and passes on its energy.
38:06This is photosynthesis, the fundamental link in our food chain.
38:15Finally, carrying energy born inside the sun's core, our photon and billions later,
38:23Finally, carrying energy born inside the sun's core, our photon and billions later,
38:30ignite the primal fires of life on our planet.
38:34The sun's light creates our fuel, drives our weather, and churns our seas.
38:45Every single day enough photons hit the Earth to power our civilization for 27 years.
38:54The sun's light is more than just warmth and heat. It provides everything we need to survive.
39:01Without light, we are nothing.
39:06All of the energy that powers our biology, the thing that makes our planet warm, that makes life possible, that all comes from the sun.
39:16Trillions of photons hit the Earth every second, each delivering life-giving energy.
39:24But for the unimaginable number who passes by, the journey is far from over.
39:32Around 80 minutes after leaving the sun, they reach Saturn.
39:38After four hours, Neptune.
39:43Once a photon leaves the surface of the sun, it's free to travel as far as it can.
39:48And as far as it can can be literally across the universe, billions of light years away.
39:56They shoot past the outer reaches of our solar system in 18 hours.
40:02Here, the sun is a dim speck in the distance.
40:06But the photons keep going out into deep space.
40:13In 1,200 years, some of the photons reach the red dwarf star system, Kepler-62,
40:21a solar system with potentially habitable Earth-like planets.
40:27In our galaxy, there are billions of Earth-like planets.
40:32If there is life out there, can it see the light from our sun?
40:39If aliens exist out there, they could easily see the light from our sun.
40:44If they're sufficiently nearby, the sun might be a naked-eye star in their sky.
40:49Or with telescopes, they would be able to detect the sun even from vastly greater distances.
40:55So there's a distinct possibility that aliens are studying our sun right now
41:00without realizing that we're here trying to study the universe as well.
41:08Hurtling on, the photons pass the Horsehead Nebula in 1,500 years
41:14and the Pillars of Creation in 7,000.
41:19At these distances, the light from our star is too small to be seen with the naked eye.
41:25But it would be visible with a powerful telescope.
41:29And with the biggest telescopes that we can create here on Earth or in space,
41:33we can actually see the light from stars at the other end of the universe,
41:37over 10 billion light-years away.
41:39And so the light from our sun is traveling across the universe.
41:45So the light from our sun, the light from the Earth, travels essentially forever.
41:50The next time you're out under a clear sky and you look up,
41:54you might want to wave because somebody out there might be able to see you and wave back.
42:00Our tiny star is visible across the universe, if someone is looking.
42:08There isn't a single place in our visible universe that you wouldn't be able to see the sun from.
42:13And maybe that's hard.
42:15Maybe there's some evidence of our existence at the other end of the universe.
42:18We won't get there for billions of years, but at least maybe we won't be forgotten.
42:24A journey that started deep inside the core of the sun with a photon.
42:30A million years to finally escape the sun's grip.
42:36Once free, our photon brought energy, heat and life to our world.
42:45Light from our sun joins light from trillions of other stars,
42:50journeying through the universe,
42:53spreading energy throughout the cosmos.