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 arm’s length.
In that tiny area covered there are almost 10,000 entire galaxies.
That’s 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 didn’t 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.
We’re 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.
That’s not to say we’d never seen other galaxies – Andromeda is visible to the naked
eye – if 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 entire “island 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 Way’s 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 stars – one 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 luminous – and 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 likely – at 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 stars’ absolute brightness.
They were the first “standard 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 that’s exactly what Hubble did right here.
He looked for Cepheid variables in the Great Andromeda Nebula – as 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 didn’t stop there.
He combined his distances with Vesto Slipher’s velocities to discover that the galaxies all
appear to be racing away from the Milky Way – paving 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.
It’s the perfect place to explore the scale of the vast universe that Edwin Hubble unlocked
for us.
Let’s take a journey.
We’re now flying through the American Museum of Natural History’s Digital Universe, rendered
by the OpenSpace Software.
Leaving Earth, the Sun, and our solar system behind, we’re zipping past the hundreds
of billions of stars of our Milky Way galaxy at a few hundred billion times the speed of light.
While we’ve 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 galaxy – once
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.
There’s Andromeda, its incredible distance first revealed to Hubble through its pulsing
Cepheid variable stars.
That’s the Virgo cluster – the nearest big city, of which our local group is an outlying suburb.
Every dot we see is a known galaxy, it’s 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 universe – galaxies 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 Hubble’s 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 exploring – if we keep looking deeper and further – who knows what we’ll
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 haven’t we seen other signs of life?
If you want answer to that, head over to It’s 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.