All language subtitles for NOVA.S51E06.Great.American.Eclipse.1080p.WEB.h264-BAE_track3_[eng]

♪ ♪

NARRATOR:
A total solar eclipse.

(people talking in background)

NARRATOR:
It's a rare and astonishing
natural phenomenon.

♪ ♪

HAKEEM OLUSEYI:
Seeing a total solar eclipse

is, like, "What?!"

You know,
you just never forget it.

♪ ♪

NARRATOR:
Solar eclipses have filled
people with wonder

since the earliest times.

It connects us with the past,

our predecessors.

They observed the same thing
we see today

whenever we look at an eclipse.

(cheers)

AMIR CASPI:
You feel a connection.

I am a part of the universe,
I am a part of the solar system,

I am a part
of this celestial event.

NARRATOR:
Can scientists seize these
precious moments of darkness

to explore a region of the sun
normally invisible...

...its outer atmosphere,
the solar corona?

GRANT TREMBLAY:
The solar corona is
one of the great keyholes

to peer into,
to truly understand

the behavior of the sun.

NARRATOR:
Behaviors like violent eruptions
from the corona

can cause huge solar storms.

MICHAEL WONG:
The largest solar storms

could really destabilize
most of the world's technology.

NARRATOR:
Plunging cities into darkness.

With the help of eclipses,

can researchers decode
these dangerous blasts

and, one day,
learn to predict them?

ANJALI TRIPATHI:
It's completely extraordinary

that nature gives us
this opportunity

to turn off the lights.

NARRATOR:
While millions
will enjoy the spectacle,

scientists are among
the most avid eclipse chasers,

studying the sun on the ground,

in the air,

and touching the corona itself.

Their goal:

to better understand

our most important
celestial neighbor.

"Great American Eclipse."

Right now, on "NOVA."

♪ ♪

NARRATOR:
It's one of nature's
greatest spectacles.

OLUSEYI:
A total solar eclipse

is like the universe
just walked up to your door

and said, "Hey! Here I am!

I'm dynamic,
and I'm doing stuff!"

♪ ♪

NARRATOR:
And on April 8, 2024,

everybody in
the lower 48 states

can experience at least
a partial solar eclipse--

weather permitting.

♪ ♪

For the 31.5 million people

who live in
the path of totality,

the disc of the sun
will completely disappear.

TRIPATHI:
It's very emotional.

The world stops for a moment,

and you are surrounded

by a completely different
universe.

♪ ♪

♪ ♪

NARRATOR:
A total solar eclipse
only happens

because of
an astonishing coincidence.

♪ ♪

The Earth, moon, and sun
must perfectly align,

so the moon blocks
the sun's light.

♪ ♪

The diameter of the moon
is around 400 times smaller

than that of the sun.

But the moon also
just so happens to be

roughly 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 blocks the sun's light,

casting a shadow on the Earth

that plunges everywhere
it passes into darkness.

CASPI:
That experience is surreal.

It is not like any other
experience

that a human being can have.

NARRATOR:
At 11:07 a.m. local time
on Monday, April 8,

the darkest part
of the moon's shadow

hits Mexico's Pacific Coast.

Traveling at more than
1,500 miles an hour,

the shadow is
over 100 miles wide,

passing over Dallas
at 1:40 p.m.,

through Arkansas
and Illinois,

over Indianapolis at 3:06 p.m.

and Buffalo at 3:18 p.m.
local time.

This shadow will exit
continental North America

at 4:38 p.m.,
after touching 15 U.S. states.

TRIPATHI:
It's a completely

extraordinary coincidence

that we get the angles
just right to make this work.

If we were anywhere else
in the solar system,

we would not have
this perfect alignment.

NARRATOR:
And if the moon were any closer
to Earth or any larger,

it would completely obscure

the object the scientists
are trying to study...

...the sun's outer atmosphere.

It's called the corona.

(people talking in background)

NARRATOR: During a total
eclipse,

the corona comes into view

as the moon passes
in front of the sun.

So the moon
has just made contact

and started covering
the sun's disc,

and we call that first contact.

And then,

the disc of the moon slides down

and covers the disc of the sun.

And we call that second contact.

This is the magic moment,

this is what
we're all waiting for

in a total solar eclipse.

This is totality.

The entire disc
of the sun is covered,

and that allows
the sun's atmosphere

that we call the corona

to emerge and be visible.

It just...
(makes sound effect)

...pops out,
and you're just, like...

(gasps):
Wow!

♪ ♪

NARRATOR:
But scientists on the ground

only get a chance
to study the corona

if they're in the right spot

and if the weather cooperates.

The bane of every eclipse chaser
is clouds and other weather

that keep them
from seeing totality.

♪ ♪

NARRATOR:
Statistically, Mexico should
have the clearest skies

along the path of totality
during April,

with Texas a runner-up.

But most places
north of Missouri

have less than 50% chance
of clear skies.

Standing on the center-line
of the moon's shadow

gives you the most time
to view the corona.

The last total solar eclipse
to pass across the U.S.

was in 2017.

It was
an unforgettable spectacle,

witnessed by an estimated
215 million people.

But the maximum duration
of totality

was just two minutes
and 42 seconds.

(crowd cheering)

NARRATOR:
In 2024, the maximum duration

is almost twice as long,

lasting four minutes
and 28 seconds.

♪ ♪

During the eclipse,
that gives you

a really unique opportunity
to suddenly see this corona

and to study it scientifically.

The corona is less bright--
quite a lot less bright--

than the main part of the sun,

so, normally,

when you observe the sun,

you're not able to see
that corona.

♪ ♪

NARRATOR:
The sun is so bright
that until the moon

completely covers it,
the only way

to view it safely is
to use certified solar filters

or eclipse-viewing glasses.

(crowd cheering and clapping)

TRIPATHI:
It's really exciting to watch.

But there is this real danger
of blinding yourself,

or causing
significant eye damage.

WONG:
You've got to get these
special eclipse glasses,

this special eyewear,
that block out

99.999% of the sunlight

and virtually
all of the U.V. light

that would really damage
your eyes.

♪ ♪

NARRATOR:
The human eye has a lens.

It helps focus light
onto the retina,

which contains over 100 million
light-sensitive receptor cells.

These cells translate light
into electrical signals

that the brain can read
as images.

Staring directly at the sun,

the focused beam from the lens
becomes so intense,

it can easily burn the cells
in the retina,

leaving a permanent blind spot.

♪ ♪

Eclipse glasses
will prevent this.

But the magnifying effect
of telescopes and binoculars

can still destroy your eye.

So, you see what that light did
to these viewing glasses?

It would do the same thing
to your eye.

You'd blind yourself instantly.

Even if you're wearing

certified solar viewing glasses,

you cannot look through
a telescope with them

unless there is a telescopic
solar filter

on the telescope itself.

♪ ♪

TRIPATHI:
During totality,
that total darkness,

you can actually
take off your solar glasses

and stare at the sun
for just a brief moment

and appreciate that darkness,

with that coronal light
around it,

which is one of
these amazing moments

that you can only experience

if you're actually witnessing
total solar eclipse.

♪ ♪

NARRATOR:
But on April 8,

what about the people
who are not lucky enough

to live within or travel
to the path of totality?

What can they see?

The good news is
that nearly everyone

in the U.S. lower 48
has a chance to experience

at least a partial eclipse.

♪ ♪

You see roughly ten percent
more of the sun

with every 200 miles of distance
from the path of totality.

For example,

in Atlanta, Georgia,
the moon covers

just over 80% of the sun's disc.

In Los Angeles, California,

around 50%.

While in Portland, Oregon,

just over 20% of the sun
is blocked.

♪ ♪

Imagine looking up at the sky--
with proper eye protection--

and noticing that part
of the sun has gone missing.

That is the joy and wonder
of a partial solar eclipse.

So even if you don't experience
total darkness,

you are still experiencing
this wondrous phenomenon.

♪ ♪

NARRATOR:
But only the darkness
of a total eclipse

allows us to see
the sun's outer atmosphere,

the corona.

The corona's elusive,
pearly-white cloud is made

from a state of matter
rarely found on Earth

called plasma.

OLUSEYI:
Sometimes we call plasma
the fourth state of matter.

There are many different
states of matter,

but the ones we're accustomed to
here on Earth are four:

solids, liquids, gases,
and plasmas.

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 super-hot mixture
of ions and electrons

is known as a plasma.

We don't see plasmas very often
on Earth.

Very briefly,

as part of a lightning bolt,
there'll be a plasma.

(lightning crashing,
thunder booming)

But the sun,
especially its corona,

is this incredible plasma.

♪ ♪

NARRATOR:
Although rare on Earth,

plasma is
a common state of matter

in the visible universe.

The stars we see in the sky
are made from it,

including our sun.

With 1.3 million times
more volume than 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 in the sun's core.

Here, the extreme heat
and pressure

force the hydrogen nuclei
to fuse together,

creating helium

and releasing
vast amounts of energy

as photons.

This nuclear fusion
heats the core

to 27 million degrees
Fahrenheit.

From here, the photons

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.

WONG:
The corona is called the corona

because it sort of has
this crown-like shape,

and "corona" in Latin
is the word for crown.

It's thin and wispy,
and hence very dim

compared to the actual surface
of the sun,

so we need that surface
to be blocked

in order to see the corona.

♪ ♪

NARRATOR:
But what more could science
discover

if we could get closer?

(machine whirring loudly)

In 2018,

NASA launches
a pioneering space probe

to do exactly that.

It's called
the Parker Solar Probe.

Onboard are instruments
that will change

our understanding of the sun

and study its extreme behavior.

(people talking in background)

KELLY KORRECK:
Parker Solar Probe
was conceived in 1958.

There was a big, long wait

because our technology

was trying to catch up
with our dreams.

MAN:
Go Delta.

MAN 2:
Go PSP.

♪ ♪

(inaudible) look good
and in full thrust mode.

♪ ♪

KORRECK:
Solar flares are large
magnetic eruptions

which can cause particles

to come streaming
towards the Earth.

We also have
coronal mass ejections,

which are billions of tons
of material,

equivalent to
80 million school buses,

racing towards us
at millions of miles an hour

that can do things like
interfere with satellites

or affect our power grid.

NARRATOR:
But even when the sun is quiet,

a lower-intensity,
steady outflow

of charged solar particles

forms what's called solar wind.

♪ ♪

KORRECK:
It has been a mystery
as to why that wind

is accelerating constantly
off the solar surface.

(engine roaring)

Parker Solar Probe
is named for Eugene Parker,

a very dear man who had a theory

about the origins
of the solar wind.

That paper

laid the groundwork
for the study

of the solar wind
that we know today.

♪ ♪

Parker is the fastest
human-made object.

It'll reach speeds of
430,000 miles per hour.

NARRATOR:
A four-and-a-half-inch-thick
heat shield

made from a carbon composite,

painted with heat-reflecting
ceramic paint,

protects the probe.

KORRECK:
The top heat shield is going to

experience 1,300 degrees
Celsius,

and in the back, it's going
to be room temperature.

It's important to have this
huge temperature difference.

Those instruments in the back
need to operate

in about room temperature.

NARRATOR:
Since 2018,
the probe's elongated orbit

takes it progressively
closer and closer to the sun.

♪ ♪

And in December 2021,

the team announces
a major breakthrough.

♪ ♪

KORRECK:
Parker Solar Probe
had touched the sun.

This is definitely a first.

This is the
monumental achievement

of being able to say
that we were inside

the atmosphere of a star.

♪ ♪

NARRATOR:
Some scientists assumed
the sun's atmosphere

was smooth, like a ball.

This is the boundary
where the solar wind escapes

the sun's gravity
and magnetic pull,

and spills out into space.

But Parker's data shows
it is undulating,

complex, and dynamic.

As the probe barrels
through the sun's atmosphere,

it runs into
huge magnetic structures

rising from the surface,

called coronal pseudo-streamers.

These could be responsible

for the rugged edge
of the sun's atmosphere.

KORRECK:
The particles of the solar wind
are a plasma.

We are just beginning
to learn more and more

about how they're thrown out
of the sun.

Knowing the shape
of that surface

is really important
to understand the formation

and acceleration
of the solar wind towards us.

♪ ♪

NARRATOR:
The strength of the solar wind

depends on the behavior
of the sun's magnetic field,

which varies
according to an 11-year cycle

called the solar cycle.

And according to that pattern,
the expected activity in 2024

could make the April eclipse

particularly interesting
for scientists.

KORRECK:
In 2017, the sun
was at a minimum.

In 2024, the difference
is going to be

that the sun
will be very active.

It will be at a maximum.

And those maximums
are where you get the show.

There could be a lot
of activity going on.

My dream is that

there is actually
a coronal mass ejection

or a flare going off
that we could see.

That would be exciting.

♪ ♪

NARRATOR:
Solar eclipses have
captivated communities

in North America for centuries.

Three hours northwest
of what is now Albuquerque,

this canyon was once home
to the Chacoans,

a Pueblo Native American people

who farmed the land here
until the 13th century.

♪ ♪

Jon Ghahate believes
they were closely attuned

to the sun's movements
and rhythms.

GHAHATE:
What makes the Pueblo
communities different from

our neighbors throughout
this entire region is that

they were permanent
agrarian societies.

To be an agrarian society,

that takes a great deal
of planning and problem solving.

If I plant too late,

I may not get
a bountiful harvest.

If I plant too early,
maybe I'll get a late frost.

So by being able to

have an understanding
of what timing means,

as it applies to the seasons,

is essential for survival.

NARRATOR:
At the top of nearby
Fajada Butte,

the Chacoans tracked the sun
to measure the seasons.

GHAHATE:
There were some slabs that
project sunlight on a spiral.

On the equinox,

the light hits
a certain point on that,

and that's why
it's called the Sun Dagger.

NARRATOR:
The equinoxes mark the moments
in the year

when day and night
are of roughly equal length.

Knowing when these happen

is vital
for deciding when to plant

and when to harvest.

♪ ♪

But the Sun Dagger
is not the only evidence

the Chacoans
watched the skies closely.

There's also a mysterious
petroglyph here

that suggests
people on this continent

may have witnessed eclipses

that have passed across
North America over centuries.

You see the circular
symbol here?

Perhaps that represents
the sun in totality.

Around the symbol,

we see lines
or curvatures,

which perhaps
we could interpret

as maybe the corona
of the sun

or the flares of the sun

that perhaps someone
might see in a total eclipse.

NARRATOR:
Scientists today
can calculate that in 1097,

a total eclipse was visible here

while the sun was nearing
the peak of its solar cycle--

solar maximum, when vast plumes

would have extended
from the corona.

GHAHATE:
That's the tantalizing thing
about it.

Much like whenever
we have an eclipse

in our time and age,
people stop work,

people want to go outside

to record
this monumental event,

because it's something
unique and special.

It connects us with the past.

Those are
the same celestial bodies

that our predecessors saw.

We're just really
the same as they were.

We just have different tools.

♪ ♪

NARRATOR:
There are 574

recognized Indigenous
communities across the U.S.,

with varying perspectives
on solar eclipses.

The Navajo people
consider an eclipse to be

a moment of renewal
that can be harmful if viewed.

Cherokee tradition says

a giant frog
is swallowing the sun,

and the frog must be scared away
to bring back the daylight.

(wind howling)

For the casual observer,

the timing
and location of eclipses

can appear random.

After the April 2024
total solar eclipse,

it will be 20 years
until another is visible

from the U.S. lower 48.

(people talking in background)

NARRATOR:
However, the period of time
between total eclipses

can be much shorter.

FILM NARRATOR:
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.

♪ ♪

(people talking in background)

NARRATOR:
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 recorded

every occasion
an eclipse was reported.

Eventually,
around the seventh century BC,

they spotted a pattern.

♪ ♪

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.

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 be another 2,000 years

before astronomers
figured out how to do that.

TYLER NORDGREN: 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 1715,
Halley published this map,

forecasting
that two weeks later,

an eclipse would pass
over Great Britain.

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.

Just 28 years earlier,

Newton had proposed
his new theory of gravity,

which allowed Halley
to accurately calculate

the path of the eclipse.

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

to the nearest hundred feet,

and when to the nearest
tenth of a second.

This is how they know
the precise path

of the 2024 total eclipse
years ahead of time.

The dance between Earth,
moon, and sun is predictable.

But the sun itself--
and its corona-- are chaotic.

Coronal mass ejections
can disrupt our power supplies

and destroy
our communications technologies.

So learning how to predict
coronal mass ejections

is the Holy Grail
of solar physics.

The sun is not some static,
unchanging ball of gas, right?

It is ejecting parts of itself
into the solar system.

The solar corona is
this dynamic and ever-changing

and incredibly beautiful
halo of plasma around the sun.

It's so important
in so many ways.

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.

Earth also has a magnetic field.

It's formed by our planet's
spinning liquid metal core

and gives us our magnetic
north and south poles.

But the sun has even
stronger magnetic fields,

created by the movement of
electrically charged particles

churning beneath the surface.

Because the plasma is moving
faster in some regions,

these fields bend and twist...

...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 particles,
they show up as the bright lines

and loops of plasma
we see in the corona.

But these field lines can snap.

TREMBLAY:
The plasma is now
free of its chains,

its anchors from the sun,

and it's free
to blast off into space.

NARRATOR:
In a coronal mass ejection,

the corona can throw a billion
tons of plasma out into space...

...at speeds of almost
2,000 miles per second.

When a coronal mass ejection
heads our way,

Earth's own magnetic field
normally deflects it,

protecting the planet.

But a large
coronal mass ejection

can overwhelm
our magnetic defenses

with devastating consequences.

OLUSEYI: A coronal mass ejection
can stream toward the Earth

and disrupt our technologies,

burn out power stations,
damage sensors on satellites,

wreaking havoc,
so, we really need to be able

to predict these things.

♪ ♪

NARRATOR:
In June 2023,

the Parker Solar Probe
makes a giant leap

towards understanding
the mechanisms

that project solar material
towards us.

The probe flies close enough
to the surface of the sun

to examine
the origins of the solar wind.

♪ ♪

The sun's surface is
a superheated honeycomb

of churning plasma cells,
each the size of Texas.

Here, magnetic plasma loops

get dragged around and collide,

triggering explosions that
release vast amounts of energy

and catapult streams of plasma
away from the sun.

Scientists have calculated
there are thousands

of these "jetlets"
all over the sun's surface--

proof that they can
give birth to the solar wind.

This was a theory as to how some
of the solar wind was formed.

As Parker got closer,
it showed that this theory

is actually at work.

When Eugene Parker
proposed these theories,

they seemed
like science fiction,

and now they're
becoming science fact.

NARRATOR:
Soon, a new NASA mission,

called PUNCH,
will launch four cameras

that will orbit Earth
to continuously map

not only how the solar wind
flows towards

and around our planet,

but also across
the entire solar system.

So that's from space...

NARRATOR:
Craig DeForest leads the team.

But it doesn't
rule out...

DEFOREST:
The four cameras separate out

all the way around the world,

looking out
in different directions.

We synchronize them, so they're
snapping pictures

at the exact same time

to image those clouds
of material in all directions,

in three dimensions, as they
streak across the solar system,

sweeping out and past us.

With a system like PUNCH,

we would be able
to track the events

all the way
across the solar system.

This is revolutionary.

We expect to be able
to greatly improve

forecasting of space weather.

♪ ♪

NARRATOR:
Back on Earth,

in October 2023, Craig gears up

to test a new version
of an old instrument

that, for the first time,
could make the sun's

elusive and violent corona
visible

to any of us at any time.

It's called a coronagraph.

DEFOREST:
What a coronagraph does
is interpose a manmade object

in front of a telescope so
that we can block out the sun,

just like the moon would do,

and see the corona around it.

NARRATOR:
But coronagraphs have
limitations.

It's almost impossible to
block enough of the sun's light

to see the corona,

unless they are either
incredibly precise and expensive

or they are deployed in space,

above the Earth's
light-scattering atmosphere.

It allows the camera to see a
perfectly uniform field of view.

NARRATOR:
The team hopes to produce

the first-ever coronagraph
that anyone can download,

3D-print, and fit onto
a telescope at home.

No, there you go--
that's it.

Oh, there it is,
perfect.

We expect to refine the design
and be able to publish

a design that will access
the corona

on any sunny day.

NARRATOR:
To help them test this device,

the team has chosen
a special day.

Over Albuquerque, New Mexico,
today, there will be

an annular solar eclipse.

♪ ♪

The moon's orbit
is not a perfect circle.

It's very slightly elliptical.

So, when the moon
is farther from the Earth,

it appears smaller,

and doesn't completely cover
the sun,

creating an annular eclipse,

also known as a
"ring of fire" eclipse.

We have a special case,
where the moon

does 90% of the work.

The sky is much darker.

(people talking in background)

NARRATOR:
By complete chance,

the annular eclipse coincides

with the Albuquerque
International Balloon Fiesta--

the world's largest gathering
of balloonists.

Today, we have 550 balloons in
this beautiful Albuquerque sky.

We'll have somewhere
between 800,000 and one million

come through our gates.

We just got really lucky
when we saw

that the eclipse was going
to coincide with our event.

We couldn't be happier.

JUDITH NAKAMURA:
I think the crowd is going
to be in awe

of getting to witness
this once-in-a-lifetime event,

because it's not happened
here before.

We just have to thank
Mother Nature

and the calendar
lining up together.

So we are about
to have first contact.

Three, two, one--
oh, yeah, you see it.

Right on the top.

WOMAN:
Ooh, and there's a bite!

♪ ♪

NARRATOR:
As the moon begins
to line up with the sun,

everything starts to get...
weird.

WOMAN:
Because the sun is
turning into a crescent sun,

the shadows change shape.

So it's one of the most eerie
things about an eclipse,

is the shadows
changing shape.

♪ ♪

All right, we have annularity.

(crowd cheers and applauds)

MAN:
All right.

(people talking, exclaiming
in background)
So cool!

CHILD:
This is so beautiful!

(people talking in background)

CHILD 1: Lookit!
CHILD 2:
It's a perfect circle!

NAKAMURA:
What a spectacular,
awesome sight.

Thank you, Mother Nature.

Thank you, Mother Nature,
and thank you, Balloon Fiesta.

DEFOREST:
This is phenomenal!

The visceral reactions
that you feel during

the approach and during
the annularity itself are,

it's very hard to describe.

It's, it's very moving.

(mouths)

DEFOREST:
Annular eclipses are phenomenal.

If you can ever get to the path
of a total solar eclipse,

it is incredible
and life-changing.

We won't know

until we analyze the data
that we got today

just how much
of the corona we saw.

So if you look,

if I turn this thing
on and off...

(murmurs)
So this is our coronagraph.

Look at that--
they seem to line up.
Perfect.

So I think we've
seen the corona.

Yeah, I mean, I think

that there's a really good
possibility.

♪ ♪

DEFOREST:
What we're looking at
is the very first data,

and what we found is, yes,

it looks to me
like it's the corona.

We're not done yet--
we have more analysis to do.

We've really just begun.

♪ ♪

NARRATOR:
During the April 2024
total eclipse,

amateur astronomers will work
with scientists

to study how the corona
changes in real time.

(people talking in background)

CASPI:
Citizen scientists,
or community participants,

they're going to get training
and we're going to deploy them

all along the eclipse path,
from the very edge

of the United States in Texas

all the way to the other edge
in Maine,

where they will be able
to observe

the eclipse shadow
passing over each one of them.

And that way,
we can put together

all of their observations

into one hourlong movie
of totality.

And so that gives us information
about how the corona is evolving

and changing over a period
of one hour.

♪ ♪

NARRATOR:
These citizen scientists
may play a role

in solving one
of the most enduring

mysteries of the corona.

♪ ♪

In the late 1800s,

a team of astronomers studying
the corona during an eclipse

made a surprising discovery.

In 1869,

there was a total solar eclipse

visible from the United States.

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 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.

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
that had been discovered.

NARRATOR:
Scientists gave this
strange new element a name:

coronium,

because it had been discovered
in the corona.

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.

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 the hottest thing

you will ever see
with the human eye.

NARRATOR:
The corona is about
two million degrees.

And that's a problem.

The surface of the sun
is only about 10,000 degrees.

How can the sun's
outer atmosphere

be hotter than its surface?

It seems to defy
basic laws of physics.

♪ ♪

Back in 2017,
in search of answers,

scientists came up with a plan

to not only extend viewing time,
but also avoid

any clouds
that might obscure the eclipse.

Amir Caspi and his team
fly two NASA jet aircraft

fitted with telescopes
above the clouds,

and track the eclipse

from an altitude of 50,000 feet.

CASPI:
By getting above
90% of the atmosphere,

above 90% of the water vapor,
we can access wavelengths

that we normally wouldn't
be able to on the ground.

NARRATOR:
They hoped their data might
shed light on why the corona

is so much hotter than
the surface of the sun.

CASPI:
And the idea is

that they pick up the track

and follow the track
straight through...

NARRATOR:
The jets could not keep up
with the eclipse shadow

traveling around
1,500 miles an hour,

more than three times
as fast as the planes.

But by flying two jets
along the path of the eclipse,

Amir extended the viewing time
to over seven minutes.

The instruments
aboard Amir's jets

could image
the infrared radiation

emitted by the corona
in high resolution.

JENNA SAMRA:
Infrared radiation is special
because it allows us

to probe
the corona's magnetic field,

and the corona's magnetic field

is critically important
for pretty much

everything that happens
in the solar corona.

NARRATOR:
The infrared images
of magnetic structures

in the corona collected
by Amir and his team in 2017

gave some unexpected results.

One of the things
that we noticed is that,

structures called prominences.

This is material
from the solar chromosphere,

the layer
just above the surface.

Its temperature is only 10,000,
20,000 degrees Celsius.

Other structures,
what we call active regions,

those are
at millions of degrees.

And we saw that prominences
and active regions

were glowing with approximately
equal brightness

in the infrared images.

That's something
that boggled our minds,

because they are a hundred times
different in temperatures,

so how could they be glowing
at the same intensity?

NARRATOR:
What are the physical
mechanisms

that cause these dramatically
different regions

to emit infrared equally?

2024 gives us a new opportunity
to study the corona

and answer some of the questions
that we opened in 2017.

NARRATOR:
In 2024,

can new instruments making even
more detailed measurements

of infrared radiation

help us explain
these surprising observations?

Here's your incoming vector,
right?

NARRATOR:
Jenna Samra
is looking for clues.

She and her team have built
their own spectroscope

that also measures
the exact brightness

of the infrared light.

And they'll install
this sensitive equipment

onboard a Gulfstream V jet

to track the eclipse
from the air.

Models suggest there
are infrared wavelengths

where the corona emits light

that we've not yet detected
with instruments.

These could eventually
help us measure

the corona's magnetic field,

which stores the energy
that heats the corona.

SAMRA:
Physicists have predicted
a number

of these bright wavelengths,
called emission lines,

and our spectrum should
encompass about 20 of these,

and about half of these
have never been seen before.

NARRATOR:
Jenna wants to find
those missing lines.

But what if they aren't there?

Would that mean the physicists'
predictions are wrong?

For now,

they're just at the start
of their investigation.

Our instrument is going
to be a stepping stone

for understanding
the, the physics of the corona,

including predicting
solar flares

and coronal mass ejections.

NARRATOR:
But in a jet moving at over
500 miles per hour,

how can you keep the eclipse
perfectly centered

so the spectroscope
can take reliable measurements?

SAMRA:
The apparent position of the sun
starts moving around.

So this mirror actually
tracks the sun.

It's moving
a thousand times a second

to basically take out
the turbulence of the airplane.

The mirror is auto-correcting.

It's getting a signal
from the camera, it's saying,

"Oh, the sun has moved off
of center.

Bring it back to center."

NARRATOR:
While Earth-bound scientists
are limited

to studying this eclipse
from one angle,

viewing from space
will give scientists

an entirely different
perspective

on how the sun's corona
and its magnetic fields

are shifting, heating,
and cooling during the eclipse.

The Parker Solar Probe
will be looking at the sun

from 90 degrees
in relation to the rest of us

here on Earth

during the 2024 eclipse.

This will give multiple
perspectives on the corona

and allow scientists
to compare real-time data

from different angles.

KORRECK:
I'm so excited
for the 2024 eclipse.

It's been a long time coming
to really understand our star,

the sun.

NARRATOR:
With clear weather, spectators
under the path of the eclipse

can enjoy totality for
almost four-and-a-half minutes.

But as the moon
begins to reveal the sun,

further cosmic treats await.

Here's the thing
about the moon--

it's not a smooth
ball.

There are mountains,
there are valleys.

So between those valleys
and peaks,

you get light of the sun
peeking through,

and those little bright dots
look like a string of beads.

We call that Baily's beads.

So we can actually see
the topography of the moon

illustrated and amplified
by the light from the sun.

NARRATOR:
As more sunlight creeps
around the edge of the moon,

there's one final,
astonishing display.

Then you have
this big bright spot,

and this is known
as the diamond ring.

It is stunning.

It's beautiful,
and you don't want to miss it.

(crowd cheering and applauding)

NARRATOR:
The 2024 eclipse

can teach us more
than ever before

about our nearest star

that gives us life on Earth.

Total solar eclipses are amazing
celestial events

to see,
and it's just awe-inspiring

to experience
something so extraordinary.

DEFOREST:
We are in a golden age
right now

of solar physics.

♪ ♪

Our understanding
of what the sun is doing

is going to evolve dramatically.

NARRATOR:
Countless people
around the world

and across millennia have gazed

with wonder and awe
as the sun disappears.

It's how we as human beings
interpret this event

that has been going on
as long as

human beings have been
on this planet.

TREMBLAY:
Let me tell you,

you have never seen a shadow
this spectacular.

It is a truly remarkable event,
because you'd have to wait years

for the next total eclipse
to go over your head.

NARRATOR:
31.5 million people
live in the path of totality,

a rare moment when
the celestial dance comes home.

You don't want to miss this
opportunity to see the eclipse.

Yeah, don't miss it!
(laughs)

♪ ♪

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