All language subtitles for 26EC92568DFB369CD00276D3626D65E0_eng

is beautiful but complex.

The skies dance with colour.

Shapes of great geometrical beauty form
and disappear.

And the planet itself is constantly
transformed.

But this seemingly infinite complexity is
just a shadow of something deeper.

The underlying laws of nature.

The world we live in is beautiful to look
at.

But it's even more beautiful to
understand.

Light is our window on the universe.

By understanding how light is emitted by
the sun.

And how it interacts with the oceans,
atmosphere and life on our planet.

We can explore worlds beyond our solar
system.

And even search for the tell-tale
signatures of life.

Amongst the stars.

Night on our planet seems eerie.

Other.

As if all the colour has drained away.

But in a few places on Earth.

On just a handful of nights in the year.

Colour bursts through.

10,000 years ago at the end of the last
ice age.

The ice sheets melted.

And this part of Iceland rose up.

Grew the coastline back.

That left the Sköa River to tumble over
the old sea cliffs to form that.

Sköafoss.

One of Iceland's great waterfalls.

When the sun, moon and the earth align.

Moonlight interacts with the spray at the
foot of the falls.

But the Federiges are using a revolution.

Let's perform a moon brain.

Light leaves the sun,
travels 93 million miles across

space and reflects off
the surface of the moon.

It enters the Earth's
atmosphere, bounces in

and out of water
droplets in the waterfall.

It enters my eye.

That sends a signal
to my brain and I

reconstruct that signal
as something beautiful.

But the moon, though, isn't just
beautiful.

It's physics.

Understanding why something's the colour
it is tells you something.

It tells you about its structure,
about the processes going on inside,

about its history even.

And because light travels
freely across the universe,

we can explore distant
worlds using light alone.

And we can tell their stories too.

The reflected light from the moon has its
origin in our star, the sun.

Stars illuminate the universe.

They are the source of the light that
bathes the planets.

But the processes by which light is emitted
by the stars can be explored here on Earth.

On 31st August 2014, a vast chasm opened
up.

In central Iceland.

At its peak, the Badabunga
volcano spewed out

350 cubic metres of
molten rock every second.

Producing light so bright it

could be seen from space.

And just like the sun, lava glows because
it's hot.

Just look at that.

It's been months since the eruption,
but it's steaming away back there.

We're actually fortunate that it erupted
here.

The helicopter pilot told me that if it
erupted on the glacier, then we would have

been plunged into a
perpetual nuclear winter

and civilisation would
have been destroyed.

That's not actually quite right, but it
would have been significantly worse.

The amount of ash
that went up into the

atmosphere would have
been really considerable.

You get a sense of the power and violence
of the earth.

Because we're blissfully unaware of it
usually.

When it breaks through the surface,
you see what it can do.

Today, the lava has cooled into matte
black rock.

But it's still giving off light.

The thing is, everything's hot.

Everything has a temperature.

But if it's cold, it just emits light that
we can't see.

This camera can see it, though.

It's called infrared light.

And you see there that this lava is
glowing brighter than the background.

It means it's hotter.

So, although we can't see it, everything
shines.

Light fills the universe.

Radio waves are light.

X-rays are light.

Visible light is simply the part of the
spectrum we can see.

Matter, like lava, or you and me, is
made up of electrically charged particles.

Here's one, moving along.

Say it's an electron.

Temperature is a measure
of how fast those particles

are moving around,
how fast they're jiggling.

So, in something
hot, these particles are

always bouncing around
and changing direction.

Now, here's a fundamental law of the
universe.

When a charged particle changes direction,
it emits light.

A particle called a photon.

Light can be thought of
as a stream of photons,

particles whose energy
corresponds to their colour.

Cooler things, like solid black lava,
emit lower energy photons, infrared light,

which our eyes can't detect.

As things get hotter, they can radiate
higher energy photons.

At 1,000 degrees
Celsius, molten lava shines

with mainly red light,
which our eyes can detect.

The surface of the sun is 5,500 degrees
Celsius.

So, it can also produce higher energy
green and blue photons alongside the red.

The white light of the sun is made up of
all the colours of the rainbow.

And when it reaches the Earth,
those individual colours are revealed.

Photons from the sun rain down and enter
water.

They reflect off the rear face,
out of the front again, and into your eye.

But the blue photons, the higher
energy ones, behave differently

to the green ones and the
yellow ones and the red ones.

They come out at a shallower angle.

And that's why you get the full spectrum
of colours from the white light of the sun.

And it's this light that paints the Earth.

The colours of our planet arise
because of the way photons from

the sun interact with the matter
from which the Earth is made.

From space, our planet is a blue world.

And that blue colour arises because of the
way light interacts with water.

And the process is linked to one of the
planet's greatest migrations.

Every spring, marine biologist Osvaldo
Vázquez heads out onto the high seas.

In search of these waters' most
awe-inspiring seasonal visitors.

Right there, coming up.

Amazing.

Humpback whales.

Humpback whales.

Humpback whales.

Humpback whales.

Every year, they make the longest
migration of any mammal on Earth.

Travelling up to 8,000 kilometres from
their feeding grounds in the Northern

Atlantic to the striking blue waters of
the Silverbank Marine Reserve.

This is the greatest nursery of humpback
whales in the world.

85% of the North Atlantic population comes
here for breeding, mating and giving birth.

So, from this place depends the survival
of this species.

The whale's life cycle is intricately
linked to the interaction between the

light of the sun and the water of the
ocean.

In order to understand their
behaviour, we need to go

beneath and to see with our
own eyes what is happening there.

Not just on the surface.

Underwater.

Turn left.

Up.

There's one.

There's a half.

Right there.

Right there.

Up again.

You saw it?

Yep, yep, yep.

We became part of a group of this group
now.

From the bottom, it looks like a whale.

The

reason humpbacks come
here to give birth is because the

shallow waters around
Silverbank are exceptionally warm.

Whales are warm-blood animals.

And when they give birth, they have a very
skinny calf with no blubber.

They need a warm environment as they had
inside the mother.

So here at Silverbank, it's warm and it's
protected.

So it's suitable for giving birth.

As photons of light rain down onto the
ocean, they strike water molecules.

And some of this energy goes into making
them jiggle around, increasing their speed

and, therefore, their temperature.

But it takes an awful lot of energy to
heat the oceans.

And so it's only here, exposed to the full
glare of the equatorial sun, that enough

energy is absorbed to raise the water
temperature to about 26 degrees.

The perfect conditions for mothers to
raise their calves.

The calves are really very cute because
they are like puppies.

But underwater, it weighs one ton.

So it's a big puppy.

But not all of the photons that enter the
water are absorbed.

Some of them bounce straight back out
again.

And it's these photons that reach our eyes
and create the blue of the oceans.

To understand why it's mainly red photons
that are absorbed rather than the blue

ones, we need to take a closer look at the
structure of water.

This is called Þingvelli.

That's a rough pronunciation.

But in Icelandic, it means Parliament
Valley.

Because the Vikings used
to meet here over a thousand

years ago and had the
world's first parliament.

The thing is, it's not
actually a valley in the

sense that it wasn't cut
by a river or a glacier.

It's actually formed by the continents
themselves splitting apart.

So that is the American continental plate
and that is the Eurasian continental plate.

And if you just go about a mile down the
road, this place is flooded.

And you can dive in it.

The rift is filled with
glacial meltwater that

seeps down from
Iceland's frozen interior.

The sun's rays are much weaker here.

But wherever sunlight hits water molecules,
it always produces the same colour.

What's that feel?

That's good.

Quite nice in here actually.

Look how blue this water is.

You can see for miles.

I've never seen anything like it.

The reason for that purity is that the
water's got 50 kilometres.

Sometimes it's going deep underground and
being filtered by these rocks.

So it's almost the coldest, purest water
you can imagine.

Really, really spectacular.

Look at that.

You can see forever.

Descending deeper into the fissure,
the effect on the colour of my drysuits

hints at the process by which the oceans
acquire their distinctive blue.

Well, now we're down at about...

well, 12 metres.

And you see that down
here, my beautiful red

diving suit is no longer
quite as red as it was.

In fact, it's looking quite black.

And the reason for that is the structure
of water molecules themselves.

See, a water molecule is an oxygen with
two hydrogens attached.

And when the light streams
into the water, the red light is

just the right energy to start
those molecules vibrating.

And they do.

They start going like that...

and like that...

and even like that.

So all the energy in the red light is
taken...

making the water molecules wobble and
vibrating.

The blue light doesn't do that.

So the blue light can scatter around in
the water relatively unimpeded.

And that's why water is blue.

Cool, isn't it?

Vibrations inside the water molecules
themselves give the oceans their colour.

The weaker bonds between water molecules
also absorb sunlight.

Together, these processes
absorb so much energy that

there isn't a lot left to
increase the sea temperature.

Which is why humpbacks must travel so far
to find water warm enough to give birth.

Because water is hard to heat up,
the temperature of the oceans remains very

stable, creating the perfect conditions
for life to thrive.

Liquid water is the essential ingredient
for any life-supporting world.

Oceans cover 70% of the Earth's surface.

Their distinctive blue,
broadcasting to the universe

the message that Earth
is a possible home for life.

And beyond the waves
on the land, we see life's

other signature colour,
a blanket of green plants.

As with all living things, they depend on
water to survive.

And when the seasonal
rains recede, the land

reverts to the arid
colours of the naked Earth.

The intense African sun delivers 1,000
watts of solar power per square metre,

baking the plains of the Serengeti to
dust.

Scorched brown, barely a single blade of
green grass survives.

For the Maasai, the dry season means
months of hunger and hardship.

Paracapuni and his son and brother must
say goodbye to their home valley.

And drive their cows across
the plains in search of enough

grass and water to keep
them alive until the rains return.

If you are looking for a place to live,
you will find a place to live.

They spend 7 days in the 방법 styling in the
area including their houses.

At the end

of their long journeys,
Maasai warriors from across the

Serengeti The Serengeti gather
on the banks of Lake Masek.

But

survival on the plains
of the Serengeti forces

Parakapuni and his family
to spend the dry season apart.

Because while he tends the cattle,
his wife, Nomi Puni, must stay behind to

look after those too young or too old to
make the trip.

And eke out an existence on the brown,
lifeless plains.

The family now has the YEAH family on a
farm.

We look after our cattle and we raise
them.

I want to see my children.

With

the cows away, the
family must survive on

their meagre stores of
maize flour and water.

The cows are the best.

We are proud of them.

Now, after four long months apart,
things are about to change.

The

coming of the rains means the grass can
grow again.

New shoots emerge, packed with the green
pigment chlorophyll,

which allows plants to harvest the sun's
energy.

And the plains are transformed from dusty
brown to vibrant green.

In just a few days, the landscape is
reborn.

I suppose we think of green as the colour
of life, but actually it's the colour that

life throws away, waste green photons
reflected back into our eyes.

Plants absorb most of the rest of the
rainbow, the blue and red photons,

and use their energy to power
photosynthesis.

Photosynthesis is the process by which
plants harness light.

They are the bridge
between nuclear reactions

93 million miles
away and life on Earth.

Energy released from nuclear fusion
reactions in the sun's core heats

everything up and shakes electrons around,
and those electrons will emit photons,

which travel across
space for eight minutes

and then hit an electron
in a chlorophyll mass.

But instead of that energy being dissipated
away as heat, chlorophyll is clever.

And ultimately, the energy imparted to
that electron is used to do all sorts of

clever things through an intricate piece
of machinery, split water up, force

electrons onto carbon
dioxide, and ultimately

build sugars, which
allows the plant to grow.

On the plains of the Serengeti,
the intricate process of photosynthesis,

means Paracapuni can begin the long
journey to rejoin his family.

I'm going to plant more trees.

I want to grow more plants, and I want to
grow more trees.

After months apart, the greening of the
Serengeti transforms the harshest of

environments into a place the Maasai can
call home.

I'm going to plant more trees and the
plants will grow on top of that.

Plants that feed on sunlight.

In this way, the sun's energy powers the
entire food chain.

But photosynthesis does more than provide
life with energy.

Around two and a half billion years ago,
it began to transform the composition of

the Earth's atmosphere itself by filling
it with a waste product, oxygen.

The gas upon which all complex life
depends.

Without air to breathe, there would be no
intelligent life on Earth.

We rely absolutely on
the oxygen that forms a fifth

of the thin blue line
that envelops our planet.

And perhaps
paradoxically, why the sky is

blue is best explained
in the dead of night.

It's a beautiful crisp autumn
night here in the south

of England, rolling hills
illuminated by moonlight.

Which is the light from the sun,
reflected off the surface of the moon.

It's quite silent actually, almost eerie.

But out there, the Earth's shadow is
racing through space.

And actually, it's just beginning to cut
in.

We're at the top, the top left hand corner
of the Moon.

On a few nights every decade, the Sun,
Moon and Earth line up to create one of

the wonders of the night sky, a total
lunar eclipse.

You get a real sense of the celestial
mechanics in action during an eclipse.

The Sun is somewhere over there behind me,
it's shining on our planet and our planet

is cast in the shadow through space which
falls on the surface of our satellite,

the Moon.

As the Earth moves between
the Moon and the Sun, it

blocks light from falling
directly onto the lunar surface.

Now the Moon is completely covered by the
Earth's shadow.

But it's not completely black,
it's glowing a deep blood red.

At the height of the eclipse,
the only photons reaching

the Moon have passed through
the atmosphere of our planet.

And it's red because of the way that light
interacts with the Earth's atmosphere.

Imagine that rain of
photons passing through the

atmosphere from the Sun,
all the colours of the rainbow.

Well, the blue photons, the higher energy
photons, have a higher probability of

bouncing off the molecules in the Earth's
atmosphere.

So they scatter around.

That just leaves the lower energy red
photons.

They have a much lower probability of
bouncing around and therefore can pass

through the Earth's atmosphere relatively
unscathed.

So they are the ones
that make it onto the

Moon's surface and
reflect back into my eye.

And that's why in a lunar eclipse you get
a blood red Moon.

And by day, the blue photons the atmosphere
scatters are what paint the skies blue.

So when you look up into the sky on a
summer's day and see that deep blue,

what you're actually
seeing is blue photons

scattering around off the
molecules in the atmosphere.

Red, green, blue.

The primary colours of our planet.

The Earth is painted by the photons that
rain down from the surface of the Sun.

But for us to see them, those photons must
take one final journey.

My name is Salma.

I live in Ramanath.

My home is very beautiful.

Salma lives with her
seven-year-old son, Majidul,

on the banks of the
Gorai River in Bangladesh.

The sky is so blue.

The plants are so beautiful.

It's so red and blue.

There are so many people.

I feel so good when I think about it.

This is a vibrant place to grow up.

But unlike the other children,
Majidul can't experience it.

No one can see my children.

They're walking around on their feet.

I'm walking on my own.

I've been walking for a long time.

I'm walking outside.

I feel so much pain in my heart.

For us to see, photons must travel into
our eyes.

But Majidul was born with severe
cataracts.

The lenses of his eyes are so clouded,
he's been effectively blind since birth.

When my son was born, he played around
here.

He was able to do a lot of things.

And I feel so much pain in my heart.

My son feels so much pain.

But today, Majidul's life is about to
change.

His family are making the eight-hour
journey to the capital, Dhaka.

Because this afternoon,
Majidul will undergo

surgery designed
to restore his sight.

If the surgery is successful, replacing
his faulty lenses with artificial ones

will allow light to travel directly into
Majidul's eyes.

It's at the back of the eye that photons
collide with cells in the retina sensitive

to red, green and blue
light, and trigger the

nerve impulses that
allow us to see in color.

Who do you want to see?

Who do you want to see now?

You?

Open your eyes.

Open, open.

Look at my eyes.

Who are you looking at?

Why don't you see?

Grip your fingers.

There.

What?

For the first time in his life, photons are
able to enter Majidul's eyes unimpeded.

For the first time in his life,
he can see.

For the first time in his life,
he can see.

Our eyes reveal to us the colours of the
earth.

Our

eyes reveal to us the colours of the
earth.

The first step towards understanding their
meaning.

The blue that signals the presence of
liquid water.

The green that marks out our planet as a
home for complex life.

And in this most distant
image of the earth ever taken

from six billion kilometres
away by the Voyager spacecraft.

The sunlight bouncing off our atmosphere
reveals our planet as a pale blue dot

hanging in the void of space.

And even from this distance,
anyone who happened to be looking

could tell our planet
contained the ingredients for life.

Because in the most delicate colour
signals, we have measured with precision

what the universe is made of.

And those signals can be glimpsed at the
very edge of our own atmosphere.

What are we drawing?

A sun dragon.

What's a sun dragon?

It's just like a sun.

And it's got smoke coming out of its
mouth.

Because it's starting to make fire on the
world.

Now, let's just do the thing.

We need to get ready to go, don't we?

Push!

For seven years, the Nation family have
been consumed by an obsession.

Ready to drop everything
at a moment's notice

in pursuit of a light
show like no other.

They've left their home on the Sussex coast
for the cold climes of Northern Norway.

73, 98, 97.

69, 98, 100.

Spending their weekends chasing one of the
planet's most extraordinary phenomena.

The Northern Lights.

Aurora Borealis.

It's an addiction.

It's an absolute full-blown addiction.

It's a buzz and it's a rush of adrenaline.

And it's a holding of your breath and...

Wow.

The aurora was once thought to be caused
by dragons fighting in the sky.

But today, we know its
ethereal light is created

by charged particles
known as the solar wind.

Interacting with the gases of the upper
atmosphere.

The oldest aurora.

She's 11.

She's fascinated by why do those different
gases make those different colours.

She's quite fascinated by it.

Oh, she likes the pink because she likes
pink.

It's her favourite colour.

So pink's cool.

Anything else, just wake me up if it goes
pink.

And Lyrica is quite a fact box on
everything.

She can explain to you
what causes an aurora,

where it comes from,
the technical names.

And, you know, what the
magnetic field does and

how it stops the solar
wind from harming us.

But the aurora is elusive.

To see it, conditions have to be just
right.

Clear, dark skies must combine with strong
solar winds.

All the family can do is wait.

Oh, oh, oh, oh.

I can see some uprights there.

Oh, wow.

Oh, yeah.

Here we go, look at it.

Beautiful.

Look at it.

Look how bright that is up there,
look.

Ah, yes!

Now that's what I'm talking about.

Look at the reds at the top.

Stunning.

Wow.

On

The left, look, there's some pink.

Yeah, it's going to take a while.

But the aurora isn't simply beautiful.

It contains information.

As charged particles strike gas atoms,
a photon of light is released.

And because the atoms of
every element have a unique

structure, each one gives off
a photon of a unique colour.

The

colours dancing across the sky reveal the
composition of our atmosphere.

And it's these fingerprints,
encoded in photons

of light, that have shown
us the entire universe.

In the last few hundred
years, astronomers have

gazed out from the
edges of our home world.

And dreamt of a universe beyond.

In the shadow of the Eiger, that is the
Sphinx.

And despite appearances, it isn't the lair
of some alpine supervillain.

It's an observatory.

It was built in 1937.

And since then, astronomers
have been coming here

from all over the world
to look at the night sky.

And by decoding messages hidden in the
light reaching our telescopes,

we've discovered the true nature of the
cosmos.

That's an aurora in a box.

It's a tube full of hydrogen gas that's
heated up.

And what you're seeing
in that pinky-red colour are

the fundamental laws of
nature themselves in action.

They tell you that a single proton,
which is the nucleus of hydrogen,

and a single electron can only behave in
certain ways.

The electrons can only go in certain
places around the proton.

So when you heat them up, they can only
jump high up.

And then when they cool down, they can
only fall back in a specific way,

releasing light of a particular energy
which equals a particular colour.

And those laws don't just apply here on
Earth.

They apply everywhere across the universe.

So anywhere that you see glowing hydrogen
gas, let's say in a nebula heated up by

young stars, then you'll see that specific
colour.

Vast clouds of glowing
hydrogen create some

of the most spectacular
sights in the cosmos.

Their pink hue revealing the identity of
the gas from which they're made.

And what's true for nebulae is true for
everything in the universe.

By analysing the light
from the stars, we know

that they're not just
twinkling lights in the sky.

They're other suns made out of the same
stuff as ours.

And if there are other suns, then there
must be other planets.

Maybe even other Earths.

By understanding the origin of the colours
of our world, the blue of its oceans,

the green of its life, and the colours
dancing in its atmosphere, we've uncovered

the colour signature of a life-supporting
planet.

And because we understand
the signature of our own world,

we can look for worlds like
ours elsewhere in the cosmos.

But here's what I think is the most
wonderful thought of all.

When you look out,
to those distant star

systems and planets,
you're connected to them.

See, an electron
somewhere out there radiated

a photon which hit an
electron in your eye.

Alien photons crossing
light-years of space, entering

your retina, and carrying
stories of distant worlds.

And in the constellation
of Pegasus, around a

sun-like star, there's
a planet called Osiris.

It's way closer to its parent
star than Mercury is to

our sun, but it's a massive
gas giant, a hot Jupiter.

And by measuring the light that shines
through its atmosphere, we've found that

the atmosphere's full of hydrogen,
and methane, and water.

And just 24 light-years away in the
constellation of Scorpius, there's a

small, rocky world, one of the most
Earth-like worlds we know.

It orbits around a red dwarf star,
which is one of three stars in the system.

A planet with three suns in the sky.

In the last 20 years, we've found hundreds
of planets around distant suns.

We've begun to analyse their atmospheres
and search for life-giving water.

Science is about gathering
data information about

the natural world and
trying to understand it.

And put like that, it seems a bit dry.

But when that information carries stories
of alien worlds around distant suns,

hundreds of light-years away, that's a
whole different thing.

Astronomy turns data into dreams.

Dreams of worlds of ice and snow.

Dreams of worlds with hemispheres in
perpetual day and permanent night.

Dreams of worlds with moons and moonbows.

And perhaps, just perhaps,
alien astronomers observing the

light passing through the
atmosphere of our blue world.

And dreaming of us.