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Thank you to Draper and its Hack the Moon initiative for supporting PBS Digital Studios.

For much of human history, people believed that the planet Earth was the center

of the universe.

That's understandable.

Earth is pretty big.

We now know that it's a speck compared to the Universe.

To get a sense of that scale, consider this grain of sand held at arms length.

In that tiny area covered there are almost 10,000 entire galaxies.

Thats a quadrillion stars, and as many planetary systems.

In fact there are surely more entire worlds in the observable universe than there are

grains of sand on this one.

Less than a century ago we didnt know that a universe existed beyond our own Milky Way Galaxy.

In the last hundred years our perspective and our understanding has grown enormously

to include countless galaxies to the cosmic horizon and almost to the beginning of time.

But before we could map the universe, first we had to discover the universe.

Were at the Mt. Wilson Observatory on the outskirts of Los Angeles, California.This

is where Edwin Hubble made a paradigm-shifting discovery: in 1924 he proved that the universe

exists beyond the Milky Way.

Oh my god.

This is the Hooker Telescope at Mt. Wilson Observatory. It is beautiful.

The whole dome is built of Carnegie Iron in the years when most of the iron was being

sent to the front for tanks.

This thing was built in 1914.

Thats not to say wed never seen other galaxiesAndromeda is visible to the naked

eyeif you have good vision.

And many nearby galaxies were visible as fuzzy blobs in our early telescopes.

But as far as we knew they were just clouds of gas inside our own galaxy.

The philosopher Immanual Kant guessed that theses nebulae might be entireisland universes”,

of their own.

In 1915, the American astronomer Vesto Slipher reported that some of those fuzzy blobs were

zipping away from us so quickly that they would surely escape the Milky Ways gravitational field.

It was a clue that they were, in fact, never within the Milky Way in the first place.

But to prove that these spiral nebulae were really island universes, we needed to find

their distances.

And distance is one of the hardest things to measure in astronomy.

So that's the desk and chair where Edwin Hubble conducted his observations of Andromeda to

calculate its distance.

He would spend nights up there taking photographs, sensitive photographic plates using a camera

much like this one.

Photographic plates go right in here.

See, when you look through a telescope it flattens 3-D space into a two-dimensional

image a dome above our heads that the ancients called the celestial sphere.

All sense of distance is lost.

For example, consider two starsone bright one dim to our eyes.

Now, perhaps those stars are identical, and the bright one is just closer to us.

Or perhaps the bright one is truly much more luminousand is at the same distance or even

further away than the dim star.

Now there are some clever ways to measure distances to stars within the Milky Way galaxy.

But in another galaxy?

Not likelyat least not until the brilliant work of astronomer Henrietta Leavitt.

A decade before Hubble made his discovery, Leavitt discovered that a certain type of

star, Cepheid variables, brightened and dimmed with a repeating period that is mathematically

related to the starsabsolute brightness.

They were the firststandard candles.”

If you time how many days or weeks it took a given Cepheid to fluctuate and you can determine

its true brightness.

So you can also figure out how far away it is just by seeing how much its true brightness

has been dimmed by that distance.

That means if you spot a Cepheid variable in a distant spiral nebulae you can find the

distance to both.

And thats exactly what Hubble did right here.

He looked for Cepheid variables in the Great Andromeda Nebulaas it was known back then.

He found that Andromeda is around 2 million light years away.

Or around 20 times the entire diameter of the Milky Way disc.

The Andromeda Nebula became the Andromeda galaxy and with more distance measurements

it became clear that all spiral nebulae were island universes of their own.

Of course Hubble didnt stop there.

He combined his distances with Vesto Sliphers velocities to discover that the galaxies all

appear to be racing away from the Milky Waypaving the way for the discovery that

the universe is expanding, meaning it must once have started with the Big Bang.

With this telescope, Edwin Hubble not only discovered the universe beyond the Milky Way,

but he opened the door to discovering its very origin.

And to our exploration of the true vastness of the universe that followed.

To see where nearly 100 years of exploration has led us, we'll need a little help from

the Digital Universe built by the Hayden Planetarium at the American Museum of Natural History.

We're on our way up.

This is where it all happens.

What a view.

We're looking down at the Planetarium from the astrophysics department.

FYI this is pretty much my favorite place in the world and I spend as much time here

as I can.

Folk here at the Hayden have turned that dome into a spaceship. It can fly us through a virtual universe

built from the most complete 3D atlas of our Universe ever compiled.

And unlike regular spaceships, this dome can fly at many times the speed of light.

Its the perfect place to explore the scale of the vast universe that Edwin Hubble unlocked

for us.

Lets take a journey.

Were now flying through the American Museum of Natural Historys Digital Universe, rendered

by the OpenSpace Software.

Leaving Earth, the Sun, and our solar system behind, were zipping past the hundreds

of billions of stars of our Milky Way galaxy at a few hundred billion times the speed of light.

While weve only mapped the locations and velocities of around 1% of those stars, that

gives us an incredible understanding of the shape and motion of our home galaxyonce

imagined to be the entire universe and now our very familiar island home.

As we zoom out, now at several trillion times the speed of light, our local group of galaxies

comes into view.

Theres Andromeda, its incredible distance first revealed to Hubble through its pulsing

Cepheid variable stars.

Thats the Virgo clusterthe nearest big city, of which our local group is an outlying suburb.

Every dot we see is a known galaxy, its position, velocity, and even stellar content

measured and cataloged.

The latest studies of galaxy motion reveal that Virgo, the Milky Way, and a hundred thousand

more galaxies belong Laniakea, a cluster of superclusters some 500 million light years

across.

As we accelerate to one hundred quadrillion times the speed of light we see the extent

of our modern mapping of the universegalaxies assembled into many vast filaments, flowing

together on rivers of dark matter to form the cosmic web, of which Laniakea is just

a part.

Edwin Hubble never imagined such a structure.

Those smaller dots at the edge of our surveys are quasars.

They look small from here, but each is a maelstrom of gas falling into a giant black hole, and

each shines out from the core of its own galaxy.

That distant light comes to us from a much younger universe.

And so we just flew through an atlas of the some of the first galaxies to ever form.

To see these most distant quasars, as well as the earliest galaxies or even black holes

or worlds around other stars, Mt. Wilson's Hooker Telescope wouldn't cut it.

For that we need state of the art modern observatories like the Gemini Observatory, and the Event

Horizon Telescope, and LIGO, which we visited throughout this series.

Yet it was Edwin Hubbles observations that opened the door to our current appreciation

of the immensity of our universe.

Knowledge that is revealed here at the Hayden Planetarium.

And hopefully our modern perspective will in turn be a gateway to future knowledge.

If we continue exploringif we keep looking deeper and furtherwho knows what well

find in the expanding horizons of space time?

Thank you to Draper and its Hack the Moon initiative for supporting PBS Digital Studios.

You know the story of the Astronauts who landed on the Moon.

Now, you can visit wehackthemoon.com and discover the story of the male and female engineers who guided them there and back safely.

Hack the Moon chronicles the engineers and technologies behind the Apollo missions.

Brought to you by Draper, the site is full of images, videos and stories about the people who hacked the moon

If the size of the Universe is enormous, why havent we seen other signs of life?

If you want answer to that, head over to Its Okay to Be Smart to watch Joe Hanson explore

how to calculate the possibility that advanced alien civilizations are out there.

PBS is bringing you the universe with the SUMMER OF SPACE, which includes six incredible

new science and history shows airing on PBS and streaming on PBS.org and the PBS Video app.

Watch it all on PBS.org/summerofspace.

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