Find a place far from city lights
and look up at the night sky.
On a dark, clear night, you can make out a thick band
of stars that arcs across the sky, known as the Milky Way.
Look towards the Milky Way, and you're looking into your
home galaxy, seen edge-on.
Notice the bulge of stars, here, near the horizon.
That is the galactic centre of the entire Galaxy.
From our position, it is very difficult to imagine
what the entire Galaxy looks like.
To find a better perspective,
we need to step off of our planet, like so.
As we drift out,
we begin to sense just how vast the Galaxy is
compared to our tiny solar system.
But even here, inside the Galaxy,
we can't take it all in.
We will need to rise up still further,
above the disk of the Galaxy.
No real photographs of our Galaxy exist
from this perspective:
everything we see has been reconstructed from centuries
of astronomical observations.
Let's take a moment to orient ourselves.
This is our Milky Way Galaxy.
We travelled from this point here:
our solar system,
just outside the Sagittarius Arm of the Galaxy.
The Galactic Centre we saw in the night sky,
is here, twenty-seven thousand light years away.
The spiral pattern of the stars and
the bar-structure of the galactic centre,
give our Galaxy its signature shape, called a barred-spiral.
It takes two hundred million years
for the galaxy to make one rotation around the core.
So our home planet, moving at
two hundred and thirty kilometres per second,
traces out this path through space.
From edge to edge, the entire galaxy
is at least one hundred thousand light years across.
Within that diameter,
there are around two hundred billion stars.
From this perspective, hundreds of billions
of worlds remain hidden by the vast distance.
So let's take the time to visit just a few.
Just over thirteen hundred light years
from our solar system,
is a place where stars are born.
This is the Orion Nebula, where huge clouds
of hydrogen gas regularly collapse in on themselves
and ignite into new stars.
Many of Orion's young stars are massive, and their stellar winds
sweep the gas clouds of the nebula
into these chaotic patterns.
Just as there is birth in the Galaxy, there is also death.
If we travel to a distance of only seven thousand light years
from our solar system,
we encounter a nebula of a different kind.
The Crab Nebula is the remnant of a supernova explosion.
In that event, the collapsing star threw off much of its mass
into space around itself, while its core collapsed
in on its own gravity, to form a dense, spinning neutron star
called a pulsar.
It is dying stars that release the elements needed
to create solar systems like our own, and even life itself.
We're just beginning to discover some of the billions of planets
that orbit the billions of stars in the Galaxy.
Only forty light years away from Earth is a solar system named
Trappist-1,
where seven planets are known to orbit a red dwarf star.
Incredibly, all seven planets orbit within what is called
the habitable zone, receiving just enough energy
from their sun to make life possible.
These are just the smallest glimpses of the vast
number of worlds that our galaxy contains.
This entire dynamic system may owe
much of its existence to a very strange object
that lies very near its centre:
the super massive black hole, named Sagittarius-A*.
like all black holes, it is an invisible object,
as no light can escape its event horizon.
And yet, we can see the black hole
by how it affects everything around it.
Just like planets orbiting a star,
the mass of this black hole,
four million times the mass of our sun,
draws entire stars into its orbit.
If we speed up time, we can see the nearest stars
completing their orbits at incredible speeds.
In fact, this black hole is at the heart
of our Milky Way Galaxy,
and may have played a key role, in it's formation
and helped to make our galaxy's
nearly infinite diversity possible.