All language subtitles for The Universe s07e02 How Fast.eng

Male narrator: In the
beginning, there was darkness.

And then... bang.

Giving birth to an endless expanding
existence of time, space and matter.

Every day, new discoveries are
unlocking the mysterious, the

mind-blowing, the deadly secrets
of a place we call the universe.

The numbers of the universe
boggle the human mind.

In the observable part of the
universe, there is something

like 100 billion galaxies--
Each with billions of stars.

The Andromeda galaxy is about
2.5 million light-years away.

The Earth is orbiting the Sun

at a speed of about
66,000 miles per hour.

Narrator: Most of us give up
even trying to comprehend such

titanic sizes, distances,
and speeds.

But are there ways to bring the
sweep of the cosmos down to

Earth to help us understand how
big, how far, and how fast?

Sync and corrections by n17t01
www.addic7ed.com

Planet Earth-- For all its wide
expanses, deep seas, and massive

mountains-- Amounts to a speck
of dust when stacked up against

the immensity of the cosmos.

The observable universe

contains on the order of
100 billion galaxies.

And then each galaxy, like the Milky Way,
contains on the order of 100 billion stars.

The numbers quickly get up into
the millions and then the

billions and even the trillions.

And by then, we've really lost

all sense of what
that really means.

Narrator: The human mind is
finely tuned to deal with the

scale of day-to-day experience.

The brain can understand
traveling 50 miles in a day.

But what about 500,000?

And a person may know what it's

like to move at 100
miles per hour.

But what about 100 million?

Numbers like millions and
billions, and certainly

trillions, are very hard for
most people to imagine,

because, frankly, most of us

don't have billions or
trillions of anything.

Narrator: So how can we ever
know the universe if our

brains can't really comprehend
its massive scale?

Doing scale models of objects
in the universe is really

helpful, because it brings
them down to sizes that we can

the night sky-- Planets, stars

and galaxies-- Down to
an earthly scale.

There are two ways
to evaluate size.

We can measure dimensions--
Meaning height, length and

width-- or calculate bulk,
also known as mass.

Bigger doesn't always
mean more massive.

Let's say a balloon has the
same volume as a bowling ball.

But the bowling ball has more
mass, because it's denser-- It's

just got more mass crammed
into that same volume.

Narrator: To help get a grasp
on some of the immense masses

floating around our universe,
astronomer Laura Danly visits a

monster truck rally...
A place where objects of hugely

differing masses often collide.

We' got everything from a

small toy truck to the
giant monster truck...

And that gives us a range of

mass that will help us
understand how massive things

are in our Solar System compared
to each other, and how massive

our own Sun is compared
to some other stars.

Narrator: We begin the
comparison with Jupiter, known

as the king of planets,
and for good reason.

Its mass amounts to more than
4 octillion pounds-- That's a

four followed by 27 zeros.

Put another way, it would take

more than 300 Earths
to match Jupiter's mass.

But even that is measly
when compared to the Sun.

The Sun is by far the most massive
thing in our Solar System.

It's about 1,000 times more

massive than Jupiter,
the biggest planet.

Well, by comparison, this car
behind me is about 3,000 pounds,

and this little toy truck
is about 3 pounds.

So that's about the same difference
between the Sun and Jupiter.

Narrator: It's a crushing difference,
as 3,000 pounds make perfectly clear.

But remember, this is a monster
truck rally, and the junk car

representing our Sun may regret
picking on little Jupiter.

The Sun is the most massive
object in our Solar System,

but it's not the most massive
star in the galaxy.

There are a lot of stars
more massive than the Sun.

Narrator: To envision the
disparity between the Sun and

a more massive star...
Let's keep the 3,000-pound junk

car as the Sun and put it up
against a 10,000-pound monster

truck representing a star
some 75 light-years away.

The difference between the
monster truck and the car is

about the same difference as a
star called Regulus-- The bright

star right in the
middle of Leo,

about 3 1/2 times as
massive as our Sun.

Narrator: Three times more massive
may not seem like much,

but don't forget we're now

pitting galactic giants
against each other.

[Engine revs]

Well, that was quite a shock.

But as you can see, three times

the mass difference
makes a difference.

If we could somehow bring
Regulus here and have it sit on

top of this Sun, that's
about the same comparison.

Narrator: But even monster
truck-sized Regulus

can't stack up to the immense

mass of the true titans
of the universe.

The most massive star we know
orbits around the Milky Way-- A

little companion galaxy called
the Large Magellanic Cloud-- In

the middle of a nebula
called the Tarantula Nebula.

That star has a kind of boring

name-- R136A-- but it's still
a very massive star.

Narrator: R136A is a young star
about a million years old.

Its surface temperature is

70,000 degrees-- about 7
times hotter than our Sun.

Before 2010, stars were thought

to form no bigger than 150
times the mass of the Sun.

But new discoveries have
doubled that limit.

We think R136A is probably about
250, maybe as much as 300

times the mass of our Sun.

Narrator: To represent this

massive star, you need a
truly monstrous truck.

This monster is 100
times heavier.

But extreme mass also comes in
small packages, where density

takes the force of gravity
into radical territory.

The greatest massive bang for
the buck we can see in the

universe comes from a stellar
object known as a neutron star.

A neutron star is the leftover
core of a supernova explosion,

with its mass packed
astoundingly tight.

It's got 1 1/2 times all of the
mass of our Sun crammed into

a volume of about
10 miles across.

If you crammed one monster truck
down into the size of a sugar

cube, that would not be

anywhere close to as dense
as a neutron star.

I'd need 10 million monster

trucks crashed down into
the size of a sugar cube.

Narrator: Stack these 10
million monster truck sugar

cubes ten miles high and wide,

and you've got yourself
a neutron star.

Neutron stars are just
bizarrely extreme objects.

If you were to try to land on
a neutron star, it would be

absolutely impossible, because
you would find that on the

neutron star you weigh about

5 billion times more than
you do here on Earth.

Narrator: But mass isn't
everything when it comes to

finding out just how big
the biggest stars can be.

The universe is also filled
with the titans that take up

unimaginable amounts of space.

Some of the tiny pinpricks
of light we see from Earth are

actually stars big enough to
swallow our entire Solar System.

Can the human mind even

comprehend the largest
star in the galaxy?

Narrator: We're bringing the
sizes, speeds, and distances of

our vast universe down to a scale
the human mind can comprehend.

The biggest thing in our Solar
System by far is the Sun.

In terms of sheer mass, it
weighs over 300,000 times more

than the Earth.

But in terms of volume, it's
also the Solar System's

physically largest object,
at 870,000 miles across.

So the Sun is really big
compared to the Earth.

It's 109 times as
wide as the Earth.

That actually means that over
a million Earths could fit

inside the volume of the Sun.

It's really big.

Narrator: But as enormous as
the Sun is in earthly terms,

our home star seems puny when
stacked against our galaxy's

lineup of stellar mammoths.

With strange names taken from
history and science, they push

the envelope of what
it means to be a star.

Consider them in turn-- Vega...
Bellatrix...

Epsilon Canis Majoris...
Dubhe... Aldebaran...

And finally, the
super-enormous Betelguese...

And VY Canis Majoris.

Oh, wow.

Narrator: Astronomer
Alex Filippenko attempts

to bring them down to Earth
in an airplane hangar.

We're here in this airport
hangar today in order to try

and illustrate the relative sizes
of stars, in particular big stars.

We're going to inflate some
balloons, and even some really

big weather balloons, and show
them in comparison with the Sun,

which we've scaled down to
the size of a bowling ball.

[Air hisses, stops]

Narrator: The bowling-ball
sun is 8 1/2 inches across,

which would make the Earth
no bigger than a tiny bead.

My two assistants are
balloon experts-- they know how

to inflate balloons with helium
and tie them off, and they know

how much to inflate them.

So they're going to inflate
these different balloons to

different sizes.

Narrator: Inflating the
balloons will take us on

a scaled-down tour of the Sun's big,
bigger, and biggest brothers.

First stop-- The star Vega.

Located in the constellation
Lyra, Vega is one of the five

brightest stars
in the night sky.

It glows blue-white, because
it burns hotter than our Sun.

Okay, so I've got my
bowling-ball Sun here.

Guys, how big is this balloon?

Let's check it out.

Right about 2 feet.

2 feet. So that's--
that's about 2 1/2imes the

size of the bowling ball.

So that's like the star Vega.

It's a bluish white star,
25 light-years away--

Very bright star in the sky.

Narrator: Next up is Bellatrix,
a star in Orion The Hunter...

The brightest
constellation in the sky.

Well-known stars pinpoint
its torso and belt.

Another blue giant, Bellatrix
is at Orion's right shoulder

and shines 240 light-years away.

So here's a bigger balloon.

What's its size?

This is 4 feet.

4 feet-- So that's about 5
1/2 times the size of my

bowling ball-- my Sun.

So this is a bigger star,
it's kind of like Bellatrix.

Narrator: Bigger than
Bellatrix is the hot blue star

Adhara-- also known as
Epsilon Canis Majoris.

Canis Majoris is a constellation whose
name translates as "The Great Dog."

Wow, now here's
a big star, huh?

This one is 12 feet.

This thing is 17 times
wider than the Sun.

That's kind of like the star Epsilon Canis
Majoris in the constellation Canis Major.

That's the same constellation
that Sirius is in.

Sirius is the brightest
star in the sky, but

Epsilon Canis Majoris is
430 light-years away.

If it were at the same distance as Sirius,
it would appear 15 times brighter.

Narrator: Almost twice as big
as Epsilon Canis Majoris is

Dubhe, a giant star on the
lip of the Big Dipper,

120 light-years away.

Wow, cool.

Well, here I see an
even bigger balloon.

What's its diameter?

Let's see.

21 feet.

21 feet.

So that's about 30 of
my bowling-ball Suns.

In fact, that's about the
size of the star Dubhe.

That star Dubhe is different
from the others that we've

seen-- it's what's
called a red giant.

It's got kind of
an orange color.

It's cooler than the blue-white
ones that we've seen previously.

Narrator: Amazingly, stars
come in larger sizes still.

And even an airplane hangar isn't
big enough to contain them.

Here's where we have to place
Aldebaran-- a monster star

known since ancient times, and once
thought to be a sign of riches and honor.

This balloon is
about 32 feet across.

Now, that's roughly 45 times
bigger than this bowling ball

which represents our Sun.

Now, this balloon then is about
the size of the star Aldebaran,

a red giant in Taurus the bull.

It's about 65 light-years away, and
its true color is roughly orange.

Narrator: Now even the
biggest balloons fall short in

representing the size of the
galaxy's biggest stars.

Betelgeuse, for instance,
is another star in orion.

650 light-years away, it is a
thousand times the size of the Sun.

Betelgeuse is so large that
its radius would extend roughly

to the orbit of Jupiter.

So if Betelgeuse was actually in
the Solar System, then all of

the eight planets would be
completely either destroyed or

- totally too hot to be habitable.
Narrator: - But the largest

known star is a beast by the
name of VY Canis Majoris.

By some estimates, it extends to
2,000 times the diameter of our Sun.

That is a truly
gargantuan star.

If there were a commercial
airplane flying just outside

VY Canis Majoris, it would take about
1,200 years to fully circle it.

Narrator: Any object on this
enormous scale seems truly alien

to the human mind...
An intimidating answer to the

"how big" question
about the universe.

No less discomforting
is "how far?"

Because distances between
planets, stars, and galaxies

stretch beyond all
human experience.

So a really great way of
bringing it home is to scale

everything down to a
more human scale.

We are better at understanding
the relative sizes of things

than abstract absolute numbers.

Narrator: Take the Moon.

It lies a little less than
250,000 miles from Earth.

You might think this
isn't all that far.

Well, think again.

Imagine if I shrank the Earth down
to about the size of a basketball.

So if the Earth was about the
size of this object here,

I would actually have the Moon be
about the size of this tennis ball.

So the next question you might
ask is, "given the relative

sizes of these things, how far apart are
they going to be from each other?"

To show you, I'm actually
going to need some help.

So Johnny is actually going to
hold the Earth for me while

I actually take the Moon and measure
out how far away it needs to be.

So here it goes.

1 foot, 2 feet...
All the way back, we're already at 10 feet.

Probably go even more...
Already past 15.

We've got to go much further.

And here we are... at 21 feet.

That's actually how far away the Moon
is from the Earth in our scale model.

Narrator: At 239,000 miles,
the Earth-Moon distance has now

become familiar to us, because
of Apollo missions to the Moon.

This is one of the few astronomical
spans we can readily understand.

In six manned Moon landings, we
learned that the travel time was

a little more than three days.

And the lunar commute has become a
part of our collective knowledge.

Engine stop.

Okay, Houston, the
Challenger has landed.

Narrator: But beyond the Moon,
the Solar System extends

to distances so vast, again,

our limited minds aren't
really up to the task.

But what would happen if we

literally brought all the
planets down to Earth?

Narrator: It can be
overwhelming to consider how

big, how far, and how fast
everything is in our universe.

Even in our Solar System, the distances
are almost unimaginably vast.

That's why we're shrinking our Solar
System and bringing it down to Earth.

Imagine if we took the
870,000 miles of diameter

of the Sun and shrank it down
to the size of a bowling ball.

What would that do
to the planets?

Well, we'd have to shrink them
down to sizes that we have here.

So we have the eight planets of
the Solar System lined out,

starting with Mercury all
the way out to Neptune.

So in this scale model, our
Earth, our home, is this tiny

little bead, while the Sun
is this bowling ball.

Narrator: These bead and
marble planets may be to scale

with the bowling ball Sun, but the
distances between them aren't.

To demonstrate that, physicist
Clifford Johnson is

going to walk the length of this miniature
Solar System laid out along a runway.

I have Johnny here, who's
going to help me measure the

distances with this
surveyor's wheel.

Okay, so let's go and
explore the Solar System.

Let's do it.

Narrator: Each foot in this
scaled-down Solar System

represents 1 million miles in the
distances between the planets.

[Wheel clacking rhythmically]

And here we are at Mercury.

And that's 36 feet.

In reality, it's actually about
36 million miles away from

the Sun.

It's amazing just how far the
very first planet of the Solar

System is from the Sun.

So now let's go on to
the second planet.

Yeah.

So here we are at Venus.

And that's 67 feet.

So this bead representing Venus
is about twice as far from

the Sun as Mercury is.

It's actually, in reality,
about 67 million miles away.

[Clacking of wheeled gauge]

And here we are at the Earth.

And that's 93 feet.

We have the Earth here
represented by this marble.

And, in fact, it's in reality 93
million miles away from the Sun.

The way the bowling ball looks,
in terms of the size, from here,

is about the size the
sun appears in our sky.

We have this blue bead
representing the Earth.

And about 2 1/2 inches away,
we have a much smaller bead

representing the Moon.

Narrator: Remember that on a
different scale, with Earth

the size of a basketball,
the Moon was 21 feet away.

To bring the whole Solar System
into the picture, we've had to

scale down the Earth-Moon
distance to mere inches.

This tiny distance between the
Earth and Moon is the limit

so far of manned
exploration of space.

Hopefully, we'll do a lot
better in the years to come.

Narrator: On our runway, Mars
orbits another 49 feet away,

or almost 142 million
miles from the Sun.

The distances beyond Mars are
about to get much, much larger.

Here we are-- Jupiter.

We're at 484 feet from the Sun.

That's actually three times as
far from the Sun as Mars is.

Narrator: With all this space
between these tiny marbles, it's

a wonder we can see the
planets from Earth at all.

It tells us that the Sun is
incredibly bright... So that the

light from the Sun can go out to
these bodies, reflect off them,

and then come back to here
on Earth for us to see them.

Okay, onwards and
outwards to Saturn.

All right, here we go.

Narrator: Our two space explorers
find Saturn 886 feet from the Sun.

In fact, Saturn, at 886
million miles away from

the Sun, is almost twice the distance from
the Sun that Jupiter is from the Sun.

So we've come a huge extra
distance and we're not even done

with the Solar System yet.

Narrator: At 1,800 feet, the
scaled orbit of Uranus stands

twice as far as Saturn-- 1.8
billion miles from the Sun.

I can hardly see
the Sun back there.

And I can actually hardly see
Neptune in the distance, which

is our next stop on our journey.

Shall we go?

Let's go.

[Wheel clacks quicker]

Jeez, that's far.

Yep.

[Laughs]

And here we are-- Neptune--
the last of the planets.

2,798 feet from our Sun.

That from our model
translates into the real-world

distance of almost 3 billion miles
that Neptune is away from the Sun.

This far out, a planet takes a long
time to do an orbit around the Sun.

The neptunian year is about
165 of our Earth years.

In fact, only one of those
neptunian years has passed since

Neptune was actually discovered.

Narrator: Viewed on this
scale, it's a wonder the Sun's

gravity has any effect at all.

And there's still more to the
Solar System beyond Neptune...

Including smaller
bodies, like Pluto...

And then, nearly a light-year
away, clouds of dark icy comets.

If the space between the
planets in our Solar System

strains human comprehension, then
the vast distances between

stars and galaxies
totally overwhelms it.

That astronomers even know how
far away stars are is a mystery

to Nora from Brooklyn, New
York, who wants to...

Nora, that's actually a
pretty complex question.

For the most nearby stars, we
look at how their positions

in the sky change with
time as Earth orbits the Sun.

For more distant stars, or stars
in other galaxies, we measure

how bright they appear to be,
compare that with their known

power, and thus determine
their distance.

Narrator: They are distances
so immense that "how big"

and "how far" are questions to challenge
anyone's power of comprehension.

But the magnitudes of the
universe also extend to speed.

What scientists have discovered
is that the universe is

super-velocity racetrack where
even giant planets move faster

than speeding bullets.

Narrator: We've seen how big
and how far things are in space.

Now we're going
to see how fast.

To do that, first we have to
understand the celestial

measuring stick known
as the light-year.

Just like it sounds, one
light-year is the distance

light travels in one year.

That amounts to about
6 trillion miles.

But that doesn't help us understand
how fast light speed itself is.

The speed of light is really
fast-- about 186,000 miles per second.

Now that's hard to conceive without an
example, imagine light were bouncing back

and forth between Los
Angeles and New York.

It could do 38 back-and-forth
bounces in one second.

Narrator: In an effort to
chase down the concept of the

speed of light, astronomer
Greg Laughlin teams with

firearms expert Michael Voight
to demonstrate some of the

fastest moving objects on Earth.

[Gunshot, ding]

The way we're going to do that
is to compare the speed of

light to the speed of something
that's really fast here on

Earth, which are bullets.

We've got a target downrange so
when it hits it, you'll hear

that ding on the end of it.

And you can kind of see how
long that actually takes.

This is a .204 Ruger.

This is the fastest commercial
cartridge on the planet right

now.

[Click]

We've got a 300-yard travel,
so I'm really going to try to

get a sense of the time that it takes
for that bullet to travel downrange.

So let's see how that works.

[Gunshot]

Nice shot.

[Gunshot, ding]

Boy, I couldn't get any sense.

As soon as I pulled the
trigger-- boom-- it hit the target.

No sense at all of
the travel time.

[Gunshots, dings]

Narrator: Because it's so
difficult for the human senses

to perceive the speed of these
bullets, Mike sets up a highly

accurate timing device
known as a chronograph.

So this is the unit that
the timer's actually in.

Inside, it's got a clock.

Okay, it looks like the
chronograph's ready here.

All right.

Let's put a couple rounds through here
and we'll see how fast this ammo goes.

And what do we have?

Wow, so that was 4,297
feet per second.

So that's about 3,000
miles per hour.

Pretty quick.

Pretty quick.

It's a little less than
a mile per second.

That roughly four times
the speed of sound.

So, I mean, I'm impressed.

But that pales in comparison
to the speed of light.

In the time that it took for
those bullets to go from the

muzzle of the gun all the way
downrange to hit the target--

During that time, light has
enough time to go all the way

around the surface of the Earth,
from Los Angeles to Paris, and

then back in that
same amount of time.

Narrator: Moving at 670
million miles per hour,

light completely demolishes any
Earthly experience of speed.

That really doesn't mean
very much to me, because the

whole distance of 670 million
miles is much larger than any

kind of distances that we
normally deal here with on Earth.

Narrator: The speed of light
and the speed of our world are

so vastly far apart, we have
to take light and slow it down

to really understand
the difference.

For that, we go back to
the speeding bullet.

At 3,000 miles per hour, we can
barely perceive its speed.

If light moved no faster
than a speeding bullet,

what would happen to the world around us
if we slowed it down by the same amount?

For example, a commercial jet
travels roughly 600 miles an hour.

So assuming the bullet
represents the speed of light,

how slow would the jet look?

At the scale where the speed
of light is 3,000 miles per

hour, then that commercial jet
is crawling along so that it

would take entire minute
to travel three inches.

Narrator: An F-15 can reach Mach
2.5-- that's over 1,500 miles per hour.

But on this slow-light scale, an F-15
needs a full minute to move seven inches.

And what about speeding
bullets themselves?

How slow do they look on
this slow-light scale?

[Gunshot]

If we go up to those
high-speed rifle bullets, then

they're making it just a
little bit more than foot--

About 13 inches-- over the
course of one minute at the

scale where 3,000 miles per hour
is the actual speed of light.

Narrator: In the real world, a snail
moves more than twice as fast.

As it turns out, much of the
cosmos is zipping around at

speeds we can't
really comprehend.

Motion is actually the normal
state of affairs in the universe.

We may think we're standing
still-- and we are, relative to

the ground-- but Earth
is orbiting the Sun,

the Sun is orbiting around the
center of our galaxy, our galaxy

is orbiting around in our
local group of galaxies.

Narrator: And all of these objects
are moving at very high speeds.

The Earth is orbiting the Sun at a
speed of about 66,000 miles per hour.

That's enough to take you around the
Earth more than twice in a single hour.

Narrator: Our Sun is rushing
around the Milky Way center at

483,000 miles per hour.

And the Milky Way itself
is flying through space at

1.3 million miles per hour.

But the speed of light is
still over 600 times faster.

The simple fact remains, we live
in slow motion compared to the

nature of the cosmos.

Modern technology doesn't travel
anywhere near the speed of light.

If we travel, say, at
commercial-jet speed, which is

a million times slower than the
speed of light, then it's going

to take us on the order of 4
million years to traverse that

distance to the closest
stars to the Sun.

Narrator: If it takes more years
to reach the nearest star

than the human race has existed,
how can any person ever really

understand the size
of our own galaxy?

Narrator: By downsizing the
biggest planets and stars and

the velocity of light speed to
the level of human experience,

we can finally begin to understand
some of the scales of outer space.

But is there a way to do the
same for the distances between

the stars... distances that utterly
dwarf the human imagination?

Although scientists measure the
enormous distance between stars

in light-years, those numbers
barely help us grasp the

expansive nature of the
galactic landscape.

So let's shrink everything down to a scale
where one light-year equals one mile.

On that scale, our Sun shrinks
down to the size of a sand grain.

We've calculated just how
many sand grains, or how many

stars, would fill our
own Milky Way galaxy.

And the number of stars in the
Milky Way is about the same as

the number of sand
grains in this chest.

Narrator: If you're counting,
that's more than 100 billion stars.

If one light-year equals one
mile, where is the nearest star?

From the vantage point of the
Griffith observatory in

Los Angeles, where astronomer
Laura Danly works, the nearest

sand grain would end up in
Hollywood, four miles away.

To help pinpoint sand grains
positioned four miles apart in a

dense city, we'll use mirrors to flash
sunlight back and forth between them.

So Aaron and Johnny have
mirrors, and they're going to

reflect sunlight to help us see just how
far away it is to the nearest star.

So I need to get a few stars to
take off to Hollywood with me.

That should do.

So Stan, Aaron, are you ready?

You're going to be the Sun staying
here at Griffith observatory.

Johnny and I are headed
out to Hollywood.

You all set?

Let's do it.

All right, let's go.

Narrator: The nearest
celestial neighbor to our Sun

isn't a single star, but
rather a grouping of three.

Two of them-- Alpha Centauri "A"

and "B"-- orbit each other, and are
about the same size as our Sun.

The third, Proxima Centauri, is
a red-dwarf star-- dim and only

about 10% as massive
as its siblings.

I'm here on a rooftop in
Hollywood, about four miles away

from Griffith observatory
there in the background.

I have in my hand a
bag full of stars.

I'm going to take out three
sand grains-- one, two, three...

Throw the rest away-- that
represent our nearest stars.

Proxima Centauri is actually
the closest star to Earth.

And on the scale of this
analogy, it's about feet

behind me, so we'll just toss Proxima
Centauri to its proper place.

Alpha Centauri "A"

and Alpha Centauri "B"

on this scale might be about two
feet apart, while our Sun is

four miles away at
Griffith observatory.

Narrator: From here, the sand
grain representing our Sun will

be impossible to spot.

This is where the
mirrors come in.

Here we are at Alpha
Centauri, but now we have

to find our own Sun.

Let's see if we can get
them to show us the Sun.

[Cell phone rings]

Hello, it's Stan.

Hey, Stan, we can't see the Sun.

You want to send us a
little sunlight our way?

Okay, Sun's coming your way.

Can't see it yet.

Uh, there.
That was a good one, yeah.

Nice and bright.

Wow, look at that.

That's incredible.

Okay, Stan, we're going to show
you the light of Alpha Centauri

now.

Yes, yes. There it is.

Yep, we saw it.

They got it.

Awesome.

He sees Alpha Centauri.

Narrator: In our region of
the Milky Way galaxy, the

typical distance between stars ranges
from three to five light-years.

With stars the size of sand grains, we could
fit about 20 in a city like Los Angeles.

But if more stars crowded any
closer to Earth, our cosmic

neighborhood would become
hazardous to life we know it.

[Explosion]

Supernova going off, which would
really cook the atmosphere.

And if another star were to pass
too close to the Sun, then the

planetary orbits would be badly
perturbed, planets could even be

lost from the Sun, sent out
into interstellar space.

It's really true that if we
didn't have these vast amounts

of real estate between the stars,
we likely wouldn't even be here.

Narrator: Cutting down the
distance light travels in a year

helps put stars in
a clearer context.

But can we do the same to
grapple with the practically

infinite dimensions
of the universe itself?

The Milky Way spans
100,000 light-years across.

And the next galaxy over is
really, really far away.

The distance to the nearest
galaxy like our own-- the nearest

spiral galaxy, the Andromeda galaxy-- is
about 2.5 million light-years away.

That's about almost 25 times the
size of the Milky Way itself.

So if you lined up 25 Milky Ways
end on end, that would stretch

to the Andromeda galaxy.

Narrator: It might be clearer
to scale things down some more,

and imagine galaxies as urban centers
spread out across the United States.

Sometimes galaxies are referred
to as star cities, and

that's a pretty good analogy.

Narrator: If envision the Milky
way galaxy at the size of

the Los Angeles metropolitan
area, roughly 100 miles wide,

then Andromeda would
be in New York.

In between, would be other
members of what astronomers call

the "local group" of galaxies.

There's basically two major
players in the local group.

There's our galaxy-- the Milky Way
galaxy-- and there's the Andromeda galaxy.

There's another smaller
spiral galaxy knows as M33.

And then we also have these
dwarf galaxies, which contain

100 million stars,
sometimes even fewer.

Narrator: But even the vast
distances that separate members

of the local group won't be
enough to save our home galaxy.

Andromeda and M33 are both
headed toward the Milky Way,

to the point where, in a few
billion years from now,

they're going to have
a close encounter.

Narrator: On a cosmic scale,
the collision seems violent.

But in fact, the stars in the
galaxies are so widely spaced,

they will weave past each
other, largely undisturbed.

If humans survive that long, they'll
hardly notice it here on Earth.

And a few billion years after that,
they'll have merged into a single galaxy.

Narrator: The Milky Way as we
know it will cease to exist.

Until that time comes, though,
the distances between

even the nearest galaxies of the
local group remain beyond our grasp.

And our galactic neighbors
represent only a small sliver of

our immense cosmos.

In the observable part of the
universe, there is something

like 100 billion galaxies--
each with billions of stars.

Narrator: If galaxies were
spaced out like urban centers

throughout the United States,
then to approximate the size of

the observable universe, the
country would have to be large

enough to wrap around the
Earth about 500 times.

Shrinking the universe down
to human scale may help us

comprehend its size, but reality,
of course, doesn't work that way.

The vastness of the universe sometimes
makes us feel really small.

We're small compared to the
Solar System, small compared to

our galaxy, compared to
the universe as a whole.

But in some ways, I think we're

not insignificant, because we're
the only creatures we know of

that have
the advanced minds and

curiosity and intellect to
think about the universe.

In a sense, we are the way in which the
universe has found to know itself.

Narrator: And so that must
mean the universe is finally

starting to figure out how
awe-inspiringly vast it truly is.

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