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In the beginning,
there was darkness...
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and then, bang...
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giving birth to an endless
expanding existence...
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00:00:09,217 --> 00:00:11,760
of time, space, and matter.
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00:00:11,803 --> 00:00:14,680
Now, see further
than we've ever imagined...
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00:00:14,723 --> 00:00:16,598
beyond the limits of our existence...
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00:00:16,641 --> 00:00:19,143
in a place we call "The Universe. "
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Chaotic and breathtaking...
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00:00:23,732 --> 00:00:27,026
their beauty forms
from the emptiness of space.
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00:00:27,068 --> 00:00:30,696
Nebulas are everything
in the galaxy that stars are not.
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Wisps of matter,
at times coming together...
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00:00:35,368 --> 00:00:38,537
at others, flying apart...
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filmy veils, billowing masses...
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00:00:41,583 --> 00:00:45,753
some dark, some glowing
in brilliant colors...
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00:00:45,795 --> 00:00:50,007
many taking the shapes of things
that are eerily familiar.
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It's interesting
when people look at nebulas...
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they sort of start
seeing things in it.
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Neither stars nor planets, they are
the crown jewels of the galaxy.
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The universe reveals
its awesome display...
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of stellar birth, death, and the cycle
of creation inside the nebulas.
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It is one of the most famous
space photographs ever taken.
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As seen
by the Hubble Space Telescope...
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it shows the Pillars of Creation...
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massive columns of dust and gas
seven light-years long.
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As big as they are,
the Pillars are just a small part...
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of an immense stellar nursery
6,500 light-years from Earth...
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called the Eagle Nebula.
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Nebulas of all kinds are scattered
among the stars everywhere...
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and are among
the most spectacular sights...
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in ours or any galaxy.
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Nebulae are beautiful,
all of them.
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They really strike the eye.
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From the Greek word for cloud,
nebulas are just that...
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clouds of interstellar gas and dust,
rarely visible to the naked eye.
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But with telescopes
in space and on Earth...
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their beauty is revealed.
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Glowing, reflecting,
or obscuring the galaxy's light...
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they are regions
where stars are born...
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where stars die,
and where explosions...
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rack the very fabric
of space-time.
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Nebulas have fantastic shapes...
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like clouds in the sky
on a summer day.
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They often evoke imagery
that hits very close to home.
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Images of flowers...
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images of insects...
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images of people.
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It's interesting
when people look at nebulas.
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00:03:07,896 --> 00:03:09,521
It's like a Rorschach test.
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They sort of start
seeing things in it.
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Although nebulas are labeled with
numbers from astronomical catalogs...
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many also have names inspired
by their locations or shapes.
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It's not difficult, for instance...
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to see why this is called
the Butterfly Nebula...
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or this is known
as the Horse Head Nebula.
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The list goes on.
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The Orion Nebula...
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the Ghost Head Nebula...
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the Stingray Nebula...
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the Helix Nebula...
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the Cat's Eye Nebula...
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the North American Nebula...
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the Pelican Nebula.
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The astonishing forms
nebulas take...
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make them the tourist
attractions of the galaxy.
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If you've got the family
in a flying saucer...
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00:04:00,448 --> 00:04:02,241
and you're careening
through the Milky Way...
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looking for an interesting rest stop,
you're going to go to a nebula.
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Like tourist attractions on Earth...
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faraway nebulas entice us
for a closer look.
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Man, it's a hike.
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One of the prime attractions
in the night sky...
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is the great Orion Nebula...
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one of the very few nebulas
you can see with the naked eye.
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On a clear night, it appears
as a fuzzy star in the sword of Orion...
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probably the most recognizable
constellation in the sky.
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The Orion Nebula is the most active area
of star formation in our galaxy.
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It lights up the sky
like nothing else.
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So this is a big one.
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In terms of nebulas,
this is the Hollywood sign.
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And the reason why travelers want
to get close to tourist attractions...
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is the same as why astronomers
want a closer look at nebulas.
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They each want to take photos.
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After all, tourism,
whether earthly or astronomical...
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is all about the pictures.
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Photographs of nebulas
occupy a real special niche...
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a very important niche, I think...
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because they
really do sit at the pinnacle...
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the confluence of art and science.
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Of course, getting
good pictures of a nebula...
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isn't just a matter
of point and click.
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In the mountains
north of San Diego...
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a group of amateur stargazers have
an especially tough road to follow...
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in seeking out nebulas
and taking great pictures.
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It is always worth
the long drive to come out here.
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00:06:02,236 --> 00:06:05,822
Night under the stars,
even if I don't do any imaging...
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00:06:05,865 --> 00:06:08,909
is worth it just to see
what I can't see from home.
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When the equipment
is this complex...
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these enthusiasts
aren't just taking pictures.
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Here, the word is "imaging"...
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00:06:21,631 --> 00:06:25,050
and their favorite targets
are the nebulas.
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Just being able to
look at them...
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and imagine what's going on
out there in that gas cloud...
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and being able to see a sense
of where stars are forming...
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it's just a great kind
of a sensory experience to have.
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In addition
to their portable telescopes...
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the group has also built a complex
of permanent observatories.
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Inside the enclosure housing
their big twenty-inch telescope...
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accomplished astrophotographer
Alan Smallbone...
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attaches a special astrocamera
to the eyepiece.
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He's preparing to image
the Orion Nebula.
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It's a very challenging object to me
because it has very light areas...
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it has very bright areas...
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it has very dark areas...
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and it's a very difficult item
to photograph accurately.
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The digital cameras used
by today's astrophotographers...
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emulate color vision
in the human eye itself.
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There are three kinds
of cone cells on the retina...
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each sensitive to either
blue, green, or red light.
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That's why those colors are
considered the primary colors of light.
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00:07:36,080 --> 00:07:38,123
But the retina
of an astrocamera...
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is a computer chip sensitive
only to black and white.
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So for color photos,
it uses red, green, and blue filters...
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taking at least one shot
with each one.
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It's often called
the RGB technique...
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and is standard for producing
more natural color.
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In capturing the Orion Nebula...
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00:08:05,067 --> 00:08:08,195
Smallbone takes time exposures
lasting five minutes...
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through each of the three filters.
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00:08:11,282 --> 00:08:14,534
But nebulas are so dim that
for the best photos...
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he often needs
dozens of exposures...
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with times totaling
as much as fourteen hours.
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No one ever said this was easy.
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Astroimaging can be very tedious
because it's very time-consuming.
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It involves long periods of time
where you're sitting...
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00:08:29,050 --> 00:08:32,010
waiting for the camera,
and the monitor's just tracking...
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00:08:32,053 --> 00:08:34,387
and there's really nothing
you can do except sit and wait.
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Later, Smallbone stacks
the raw images on his computer.
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There,
the different combinations...
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of red, blue, and green dots
work just like a color TV...
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to create every other hue
in the spectrum.
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Hours after first opening
the shutter...
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the Orion Nebula appears
in its natural colors on the screen...
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as no human eye has
the sensitivity to see it.
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The striking images
of these and other nebulas...
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demonstrate the essential reason
astrophotography is indispensable...
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when it comes to the nebulas.
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The combination
of a telescope and a camera...
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actually allows you to see details
in structures in the nebulae...
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that you couldn't see
with your own eye...
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because they're so faint
and diffuse.
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The great Orion Nebula
is well worth the attention it gets.
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Fifteen light-years across...
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it is a massive cloud,
made mostly of hydrogen.
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It is the quintessential example
of the kind of nebula...
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known as a star-forming region.
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It is the cradle
of the most massive stars...
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that are born in our galaxy.
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And it is the closest example
of that process to us.
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So when you look
at the great Orion Nebula...
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you're looking at stars being born.
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Among the thousands of infant
stars in the Orion Nebula...
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four of them dominate...
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the corners of a cluster
called the Trapezium...
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for its trapezoidal shape.
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Massive and hot,
they are responsible...
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for the brilliant
astronomical display.
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The Trapezium in the center
of the great Orion Nebula...
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is what energizes it.
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It's what makes it a nebula.
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If you didn't have the Trapezium stars,
it would be a dark cloud.
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Radiation from the Trapezium stars
sculpts the surrounding gas...
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and causes it to glow
with emitted light.
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What would it be like to fly through
the Orion Nebula in a spacecraft?
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It might look like this...
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a remarkably accurate
supercomputer simulation...
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based on detailed
Hubble Space Telescope data...
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and modeled by Vanderbilt University
astronomer Robert O'Dell.
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Traveling into the gigantic cloud...
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we see the four bright
Trapezium stars...
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00:11:20,137 --> 00:11:23,515
their 3-D positions
now clearly evident.
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Their intense energy has
hollowed out the nebula's center.
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The Trapezium stars
are so bright...
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that they would blind us
to the rest of the nebula...
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00:11:33,567 --> 00:11:37,320
if our view screen were not enhanced
to show us all the details.
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00:11:38,406 --> 00:11:40,198
The dark globs scattered about...
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called proplyds
or protoplanetary disks...
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are blankets of dust
surrounding newly formed stars...
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forced into teardrop shapes
by energetic stellar winds...
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00:11:51,085 --> 00:11:52,460
from the Trapezium.
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00:11:53,462 --> 00:11:54,796
One of them clearly shows...
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00:11:54,839 --> 00:11:58,216
a ring of debris
orbiting its central star...
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strong evidence that a new
system of planets is forming.
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Our route
out of the Orion Nebula...
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shows us the angle
at which we see it from Earth.
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00:12:11,272 --> 00:12:13,898
But at 1,300 light-years away...
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00:12:13,941 --> 00:12:17,736
it shrinks to a minor smudge
in our field of view.
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00:12:20,281 --> 00:12:23,158
Imagine how it would look
at only four light-years...
198
00:12:23,200 --> 00:12:26,161
the distance to the nearest star.
199
00:12:26,203 --> 00:12:27,245
The Orion Nebula...
200
00:12:27,288 --> 00:12:29,789
if we were as close
to the Orion Nebula...
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as the nearest star is to us,
it would be so bright...
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00:12:33,252 --> 00:12:37,005
that we wouldn't be aware
of the dark sky.
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00:12:37,047 --> 00:12:38,256
We wouldn't see
the other stars.
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00:12:38,299 --> 00:12:40,508
We would almost not be aware
of other galaxies...
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00:12:40,551 --> 00:12:42,302
just because
it would be so bright.
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00:12:44,472 --> 00:12:47,307
The whole world would be
the Orion Nebula and the Sun.
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00:12:49,977 --> 00:12:52,812
Fortunately, we live
at a point in the galaxy...
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00:12:52,855 --> 00:12:56,608
where our telescopes and cameras
can comb the heavens...
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00:12:56,650 --> 00:13:00,069
to shake loose the gems
we call nebulas.
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00:13:00,988 --> 00:13:02,781
There are five major kinds.
211
00:13:04,617 --> 00:13:08,620
Star-forming nebulas like Orion
are called H-ll regions.
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00:13:08,662 --> 00:13:10,955
H-ll describes
the thin hydrogen...
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00:13:10,998 --> 00:13:13,833
excited by hot stars
to emit light.
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00:13:15,127 --> 00:13:18,630
In other places,
there are reflection nebulas...
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00:13:18,672 --> 00:13:22,217
where the bright stars have
driven away the surrounding gas...
216
00:13:22,259 --> 00:13:25,386
leaving mostly dust
to reflect starlight.
217
00:13:26,555 --> 00:13:28,473
Planetary nebulas are formed...
218
00:13:28,516 --> 00:13:32,143
during the slow, dying stages
of ordinary stars...
219
00:13:32,186 --> 00:13:34,646
and produce some
of the most intriguing displays...
220
00:13:34,688 --> 00:13:37,607
of shape and color
in the galaxy.
221
00:13:39,026 --> 00:13:43,488
Supernova remnants are also
leftovers from stellar deaths...
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00:13:43,531 --> 00:13:48,368
but from massive stars, which end
their lives in immense explosions.
223
00:13:50,538 --> 00:13:53,248
And finally,
there are the dark nebulas...
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clouds of interstellar
gas and dust...
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00:13:55,835 --> 00:13:58,837
visible usually because
they appear in silhouette...
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00:13:58,879 --> 00:14:01,256
against the bright nebulas
behind them.
227
00:14:01,298 --> 00:14:05,301
In time, stars will burst
into existence within them.
228
00:14:07,304 --> 00:14:12,308
But the very origin of the galaxy's
clouds of stars, gas, and dust...
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00:14:12,351 --> 00:14:14,686
is the most intriguing
phenomenon of all.
230
00:14:15,271 --> 00:14:18,273
Springing from the mysterious
interstellar medium...
231
00:14:18,315 --> 00:14:21,526
the riddle of the nebulas
is how they can form...
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00:14:21,569 --> 00:14:24,654
from what is
almost nothing at all.
233
00:14:26,907 --> 00:14:29,659
Space, in its vast emptiness...
234
00:14:29,702 --> 00:14:32,245
has much more to it
than meets the eye.
235
00:14:33,372 --> 00:14:37,709
Filling the distances between the Sun
and all its galactic neighbors...
236
00:14:37,751 --> 00:14:41,796
is the neutral
interstellar medium or ISM.
237
00:14:41,839 --> 00:14:44,591
When we think about
the blackness between stars...
238
00:14:44,633 --> 00:14:47,677
we sometimes think there's nothing
there but the vacuum of space.
239
00:14:47,720 --> 00:14:50,513
But actually, even
the so-called vacuum of space...
240
00:14:50,556 --> 00:14:52,765
is full of dust and gas.
241
00:14:52,808 --> 00:14:54,142
Now, it's quite rarefied.
242
00:14:54,184 --> 00:14:55,268
How rarefied?
243
00:14:55,311 --> 00:14:57,896
Perhaps better
than the best vacuum...
244
00:14:57,938 --> 00:14:59,898
we can create
on the planet Earth.
245
00:15:02,276 --> 00:15:04,694
The particles
in the interstellar medium...
246
00:15:04,737 --> 00:15:08,823
are ninety percent hydrogen atoms,
ten percent helium...
247
00:15:08,866 --> 00:15:12,911
and trace amounts of other elements
and tiny specks of dust.
248
00:15:14,830 --> 00:15:17,332
Existence of the gas and dust
is evident...
249
00:15:17,374 --> 00:15:19,208
by looking at the Milky Way...
250
00:15:20,127 --> 00:15:22,921
the band of stars we see
in the edge-on view...
251
00:15:22,963 --> 00:15:24,964
of our home galaxy
from Earth.
252
00:15:25,841 --> 00:15:29,052
There, the dark spaces
seem to be empty...
253
00:15:29,094 --> 00:15:32,597
but in reality,
the opposite is true.
254
00:15:32,640 --> 00:15:36,559
Those spaces
aren't devoid of stars.
255
00:15:36,602 --> 00:15:40,647
They're actually dust
between us and the distant stars...
256
00:15:40,689 --> 00:15:41,898
in the plane of our galaxy...
257
00:15:41,941 --> 00:15:45,610
and they block that light,
and you see them in silhouette.
258
00:15:47,196 --> 00:15:49,405
The black lanes
of gas and dust...
259
00:15:49,448 --> 00:15:51,324
show us where
the interstellar medium...
260
00:15:51,367 --> 00:15:55,995
is clumping together to form
nebulas in their most primeval form.
261
00:15:56,997 --> 00:16:02,543
We see these dark nebulas as
shadows against the background stars.
262
00:16:02,586 --> 00:16:06,172
The Snake Nebula
is 650 light-years distant...
263
00:16:06,215 --> 00:16:09,092
and approximately
three light-years across.
264
00:16:10,636 --> 00:16:13,012
Even darker is Barnard 68...
265
00:16:13,055 --> 00:16:15,139
named for
Edward Emerson Barnard...
266
00:16:15,182 --> 00:16:17,225
the astronomer
who discovered it.
267
00:16:17,267 --> 00:16:19,018
Such nebulas
may be deep enough..
268
00:16:19,061 --> 00:16:21,771
to block light
from stars behind them...
269
00:16:21,814 --> 00:16:25,316
but the gas and dust inside them
is still very thin...
270
00:16:25,359 --> 00:16:29,153
that is
until gravity's work accelerates.
271
00:16:29,196 --> 00:16:30,905
Gravity is attractive.
272
00:16:30,948 --> 00:16:33,658
As a consequence,
we have lumps of gas...
273
00:16:33,701 --> 00:16:36,995
no matter how rarefied,
being attracted by gravity...
274
00:16:37,037 --> 00:16:41,374
until we have clumps
of nuclear material condensing.
275
00:16:41,417 --> 00:16:44,002
As gravity begins
to compress the gas...
276
00:16:44,044 --> 00:16:47,005
it starts to heat up
in temperature...
277
00:16:47,047 --> 00:16:49,549
creating the temperatures
of a star.
278
00:16:52,678 --> 00:16:55,471
The new stars
burst into existence...
279
00:16:55,514 --> 00:16:59,225
lighting up their surroundings
with colorful brilliance.
280
00:16:59,268 --> 00:17:02,395
Remaining dark nebulas stand out
in stark contrast.
281
00:17:03,063 --> 00:17:06,482
Like bright nebulas,
their shapes suggest names.
282
00:17:06,525 --> 00:17:10,028
The Elephant's Trunk Nebula...
283
00:17:10,070 --> 00:17:12,030
the Cone Nebula...
284
00:17:12,072 --> 00:17:15,074
and the Flame Nebula,
where dark and light areas...
285
00:17:15,117 --> 00:17:18,244
create one of the sky's
most dramatic images.
286
00:17:19,580 --> 00:17:22,373
The brilliant colors
of the star-forming regions...
287
00:17:22,416 --> 00:17:27,170
come from nebular gases excited
by invisible ultraviolet radiation...
288
00:17:27,212 --> 00:17:30,673
from nearby hot new stars.
289
00:17:30,716 --> 00:17:33,593
The light, the ultraviolet light
from those stars...
290
00:17:33,635 --> 00:17:37,638
is stripping off the electrons
in the gas in its immediate vicinity.
291
00:17:38,223 --> 00:17:42,101
These electrons float around
for days or weeks...
292
00:17:42,144 --> 00:17:44,854
and then ultimately find
a bare proton...
293
00:17:44,897 --> 00:17:49,567
or other positively charged nucleus,
and they'll hop on to orbits...
294
00:17:49,610 --> 00:17:52,487
and as they do,
they'll emit light.
295
00:17:56,992 --> 00:18:00,620
At the University of Rochester,
astronomer Adam Frank...
296
00:18:00,662 --> 00:18:04,540
compares the excitement of gases
in a nebula to a basketball game.
297
00:18:09,004 --> 00:18:11,255
This basketball game
is a real nice analogy...
298
00:18:11,298 --> 00:18:13,758
though earthbound,
for what happens in a nebula.
299
00:18:20,224 --> 00:18:23,601
Down on the court, you got Rochester
going up against NYU.
300
00:18:23,644 --> 00:18:27,688
The basketball players are a lot like
the stars at the center of the nebula.
301
00:18:27,731 --> 00:18:29,607
When something exciting
happens on the court...
302
00:18:29,650 --> 00:18:31,109
you'll see the crowd
getting all excited.
303
00:18:35,823 --> 00:18:39,283
The crowd stands up,
they cheer, they emit energy.
304
00:18:39,326 --> 00:18:40,493
In this case
it's sound energy...
305
00:18:40,536 --> 00:18:41,953
but in the nebula,
it would be light.
306
00:18:41,995 --> 00:18:43,788
This is exactly the same thing
that happens...
307
00:18:43,831 --> 00:18:45,623
when an electron gets
ripped off an atom...
308
00:18:45,666 --> 00:18:47,166
flies around for a while...
309
00:18:47,209 --> 00:18:48,876
and then finds another atom
to recombine with...
310
00:18:48,919 --> 00:18:50,962
and emits energy
at the same time.
311
00:18:59,346 --> 00:19:01,973
As new stars are born
within the nebulas...
312
00:19:02,015 --> 00:19:05,560
they sometimes shoot out
spectacularjets.
313
00:19:05,602 --> 00:19:09,063
This one is
three trillion miles long.
314
00:19:09,106 --> 00:19:11,524
The jets are nebulas
in their own right...
315
00:19:11,567 --> 00:19:14,652
generated by the orbiting
cloud of gas and dust...
316
00:19:14,695 --> 00:19:16,863
sending material
into the young star.
317
00:19:18,991 --> 00:19:21,576
Because of rotation,
it first forms an accretion disk...
318
00:19:21,618 --> 00:19:23,995
which is kind of like a Frisbee
spinning around the young star...
319
00:19:24,037 --> 00:19:25,997
feeding,
building the young star.
320
00:19:26,039 --> 00:19:28,541
Now, there's always
magnetic fields in all of this gas...
321
00:19:28,584 --> 00:19:30,001
and as the disk spins...
322
00:19:30,043 --> 00:19:32,461
material loads up
on the field lines, as we say...
323
00:19:32,504 --> 00:19:35,464
and it spins and then
it's flung out into space.
324
00:19:35,507 --> 00:19:37,675
Eventually, the field lines
get bent around...
325
00:19:37,718 --> 00:19:40,720
collimating the jet,
creating a nice solid jet column.
326
00:19:43,390 --> 00:19:45,224
Along with stellarjets...
327
00:19:45,267 --> 00:19:48,477
the galaxy's nebulas
display a wild variety...
328
00:19:48,520 --> 00:19:54,567
of bubbles, shockwaves, pillars,
and even mountains.
329
00:19:56,570 --> 00:19:59,697
These are called
the Mountains of Creation...
330
00:19:59,740 --> 00:20:03,534
a nebula often compared to
the famous Pillars of Creation...
331
00:20:04,620 --> 00:20:07,872
but, in fact,
ten times as large.
332
00:20:09,082 --> 00:20:11,500
Though they are
seventy light-years across...
333
00:20:11,543 --> 00:20:14,295
this image,
taken in visible light...
334
00:20:14,338 --> 00:20:16,380
shows them subtle
in appearance.
335
00:20:17,883 --> 00:20:20,301
But see what happens
when we look at a picture...
336
00:20:20,344 --> 00:20:25,348
from the Spitzer Space Telescope,
which views them in infrared.
337
00:20:27,935 --> 00:20:31,395
Infrared light is light of a slightly
longer wavelength than visible light.
338
00:20:31,438 --> 00:20:32,730
It's redder than red light.
339
00:20:32,773 --> 00:20:35,900
We commonly see infrared light
from objects like us...
340
00:20:35,943 --> 00:20:38,611
that are warm,
but not extremely hot.
341
00:20:40,530 --> 00:20:43,908
Since infrared light is emitted
by anything that is warm...
342
00:20:43,951 --> 00:20:47,078
it's often used to detect heat.
343
00:20:47,120 --> 00:20:50,581
In special cameras,
each temperature is detected...
344
00:20:50,624 --> 00:20:53,334
as an infrared color
that we can't see...
345
00:20:53,377 --> 00:20:57,380
and then it's translated
into a visible color that we can see.
346
00:21:00,133 --> 00:21:02,677
That's how infrared
can use body heat...
347
00:21:02,719 --> 00:21:06,764
to reveal some amateur astronomers
working in the dark of night...
348
00:21:06,807 --> 00:21:10,810
when otherwise we'd have to turn
on a light to see them at all.
349
00:21:12,980 --> 00:21:15,815
In space,
the same principle applies.
350
00:21:15,857 --> 00:21:19,777
This is the Eagle Nebula
as seen in visible light...
351
00:21:19,820 --> 00:21:23,948
but the infrared Spitzer Telescope
sees it in a much different way...
352
00:21:23,991 --> 00:21:29,453
revealing a region of extremely
hot dust, seen here in red.
353
00:21:29,496 --> 00:21:32,123
Now, you have to ask yourself,
what could get dust that hot?
354
00:21:32,165 --> 00:21:34,083
The stars in the nebula? No.
355
00:21:34,126 --> 00:21:36,127
They're not really bright enough,
they're not hot enough...
356
00:21:36,169 --> 00:21:37,837
but maybe a supernova explosion.
357
00:21:39,631 --> 00:21:42,508
Maybe the violent death of a star.
358
00:21:42,551 --> 00:21:46,220
A supernova would send out
a massive shockwave...
359
00:21:46,263 --> 00:21:48,431
which might have
a profound impact...
360
00:21:48,473 --> 00:21:52,435
because the Eagle Nebula is
home to the Pillars of Creation.
361
00:21:52,477 --> 00:21:54,937
Now, for the Pillars,
it doesn't look very good.
362
00:21:54,980 --> 00:21:58,899
What's going to happen
is that supernova shockwave...
363
00:21:58,942 --> 00:22:00,693
that's expanding out
from the exploding star...
364
00:22:00,736 --> 00:22:04,071
sooner or later
is going to hit those Pillars.
365
00:22:04,114 --> 00:22:07,074
And when it hits the Pillars,
it's going to evaporate them...
366
00:22:07,117 --> 00:22:09,118
and they're
going to be destroyed...
367
00:22:10,495 --> 00:22:13,914
leaving the stars that are currently
forming in the Pillars behind...
368
00:22:13,957 --> 00:22:16,625
but all that gas and dust
in those beautiful, you know...
369
00:22:16,668 --> 00:22:19,670
pillar-like shapes,
they're going to go, just disappear.
370
00:22:21,590 --> 00:22:25,134
The infrared that reveals
the fate of the famous Pillars...
371
00:22:25,177 --> 00:22:29,013
is only one tool
in the astronomer's light box...
372
00:22:29,056 --> 00:22:32,308
but the nebulas can be seen
in light of all kinds...
373
00:22:32,351 --> 00:22:37,605
stripping away shrouds that keep
their secrets otherwise hidden forever.
374
00:22:40,650 --> 00:22:43,527
In a universe filled with light...
375
00:22:43,570 --> 00:22:46,113
astronomers have learned
to look at the stars...
376
00:22:46,156 --> 00:22:48,699
by analyzing light
of different kinds...
377
00:22:49,826 --> 00:22:53,162
such as the infrared images
from the Spitzer Space Telescope.
378
00:22:57,584 --> 00:23:02,421
Infrared is only one region
on the electromagnetic spectrum...
379
00:23:02,464 --> 00:23:05,216
an immense scale we use
to measure the wavelengths...
380
00:23:05,258 --> 00:23:07,802
of all kinds of radiation.
381
00:23:07,844 --> 00:23:12,223
At one end are radio waves
with the longest wavelengths.
382
00:23:12,265 --> 00:23:15,893
At the other end are gamma rays
with the shortest.
383
00:23:15,936 --> 00:23:19,522
In between are the other bands,
including visible light...
384
00:23:19,564 --> 00:23:23,901
which is such a tiny fraction
of the whole, it's difficult to imagine.
385
00:23:26,613 --> 00:23:28,948
How small is the visible spectrum?
386
00:23:30,617 --> 00:23:32,743
If you had a reel of movie film...
387
00:23:32,786 --> 00:23:35,579
representing the entire
electromagnetic spectrum...
388
00:23:37,749 --> 00:23:43,421
stretching 2,500 miles
from California to Alaska...
389
00:23:45,424 --> 00:23:47,758
the section containing
the visible spectrum...
390
00:23:47,801 --> 00:23:52,596
would fall somewhere in the middle,
near the University of Washington.
391
00:24:06,987 --> 00:24:10,739
This frame is the whole
visible spectrum.
392
00:24:10,782 --> 00:24:14,452
It is one frame
in over 2,000 miles of tape...
393
00:24:14,494 --> 00:24:17,955
and it's everything
that the human eye can see.
394
00:24:17,998 --> 00:24:19,290
The importance of this frame...
395
00:24:19,332 --> 00:24:22,084
is that stars emit
almost all of their light...
396
00:24:22,127 --> 00:24:24,128
in this part of the spectrum.
397
00:24:26,465 --> 00:24:28,632
And even though
the light is visible...
398
00:24:28,675 --> 00:24:32,303
it still contains hidden tools,
helping us to explore nebulas...
399
00:24:32,345 --> 00:24:35,931
in ways that our eyes cannot
do entirely on their own.
400
00:24:37,058 --> 00:24:40,811
The secrets are
in the spectrum itself.
401
00:24:40,854 --> 00:24:44,440
The visible light in this lamp
comes from hydrogen gas...
402
00:24:44,483 --> 00:24:47,818
excited by electricity
to form a glowing plasma...
403
00:24:47,861 --> 00:24:50,237
similar to what happens
in a nebula.
404
00:24:50,280 --> 00:24:53,032
By viewing the lamp
through a diffraction grating...
405
00:24:53,074 --> 00:24:57,119
we can split the light up into
three narrow lines on the spectrum...
406
00:24:57,162 --> 00:25:00,998
a virtual fingerprint of light,
unique to hydrogen alone.
407
00:25:01,041 --> 00:25:03,542
So in the spectrum,
you see three features.
408
00:25:03,585 --> 00:25:04,710
One is red...
409
00:25:04,753 --> 00:25:06,086
one is a light blue...
410
00:25:06,129 --> 00:25:08,339
and the other is a deep blue.
411
00:25:08,381 --> 00:25:12,343
This pattern of wavelengths
is absolutely unique to hydrogen...
412
00:25:12,385 --> 00:25:14,553
and there's no way
to confuse hydrogen...
413
00:25:14,596 --> 00:25:17,223
in the spectrum of a nebula
with any other element.
414
00:25:21,561 --> 00:25:24,438
It's like the crowd
at our basketball game.
415
00:25:24,481 --> 00:25:29,235
The cheering mass is actually
made up of individual fans...
416
00:25:29,277 --> 00:25:32,321
each with his or her own
distinctive voice...
417
00:25:32,364 --> 00:25:34,573
voices you could
make out clearly...
418
00:25:34,616 --> 00:25:37,076
if you had a way to isolate them.
419
00:25:40,080 --> 00:25:44,542
Isolating the individual spectral lines
of the elements within nebulas...
420
00:25:44,584 --> 00:25:48,379
has allowed astronomers
to create images truly worthy...
421
00:25:48,421 --> 00:25:52,049
of these tourist attractions
of our galaxy.
422
00:25:52,092 --> 00:25:55,010
By using what are called
narrow-band filters...
423
00:25:55,053 --> 00:25:57,179
corresponding to single lines...
424
00:25:57,222 --> 00:26:00,099
astronomers have given us
another way of seeing things...
425
00:26:00,141 --> 00:26:02,309
we can't see by ourselves.
426
00:26:05,355 --> 00:26:09,066
When the Hubble Telescope
photographed the Pillars of Creation...
427
00:26:09,109 --> 00:26:13,362
it used one filter to isolate hydrogen's
brightest red line...
428
00:26:13,405 --> 00:26:17,283
another to isolate sulfur's
even redder line...
429
00:26:17,325 --> 00:26:21,078
and a third to capture
oxygen's line of blue green.
430
00:26:22,622 --> 00:26:24,873
Image specialist Zoltan Levay...
431
00:26:24,916 --> 00:26:28,252
assembles the components
into a full color image...
432
00:26:28,295 --> 00:26:31,755
that reveals more
than the sum of its parts.
433
00:26:31,798 --> 00:26:35,342
By taking images
of the nebula through a filter...
434
00:26:35,385 --> 00:26:37,261
that isolates the light
of a particular element...
435
00:26:37,304 --> 00:26:42,099
we are seeing the distribution of
that element throughout this nebula.
436
00:26:42,142 --> 00:26:43,142
But to a larger extent...
437
00:26:43,184 --> 00:26:47,229
we're seeing how the physical
conditions vary across a nebula.
438
00:26:49,190 --> 00:26:55,613
If the true colors of hydrogen, oxygen,
and sulfur lines were combined...
439
00:26:55,655 --> 00:26:58,866
the image of the Pillars
would look something like this.
440
00:27:00,660 --> 00:27:03,245
But the Hubble team
translates each element...
441
00:27:03,288 --> 00:27:05,539
into one of light's primary colors.
442
00:27:07,042 --> 00:27:09,668
Oxygen's blue green
is assigned to blue.
443
00:27:10,712 --> 00:27:13,088
Hydrogen's red
is assigned to green.
444
00:27:14,174 --> 00:27:18,677
And sulfur, similar to hydrogen
in color, is assigned to red.
445
00:27:20,305 --> 00:27:23,265
Sometimes called false color...
446
00:27:23,308 --> 00:27:26,310
the image is a better display
of material reality.
447
00:27:28,271 --> 00:27:30,314
This I would refer to
as representative color...
448
00:27:30,357 --> 00:27:31,982
the way we've constructed
this image.
449
00:27:32,942 --> 00:27:37,655
The colors may not appear the same
as the colors we would see...
450
00:27:37,697 --> 00:27:40,491
if we were looking at this
with our unaided eyes...
451
00:27:40,533 --> 00:27:42,159
or through a telescope...
452
00:27:42,202 --> 00:27:45,704
but they represent the physical
processes that are happening here.
453
00:27:48,041 --> 00:27:50,459
The hydrogen, oxygen,
sulfur filters...
454
00:27:50,502 --> 00:27:53,879
as combined this way are known
as the Hubble palette...
455
00:27:53,922 --> 00:27:57,257
which is used widely in nebular
photography of all kinds.
456
00:27:58,802 --> 00:28:03,972
It shows us not only the colorful chaos
of star-forming nebulas...
457
00:28:04,015 --> 00:28:08,977
but also the striking images
of the places where stars die.
458
00:28:18,738 --> 00:28:21,990
These beautiful, complex gems
that dot the cosmos...
459
00:28:22,033 --> 00:28:24,368
marking the demise of stars...
460
00:28:24,411 --> 00:28:30,708
are called planetary nebulas,
a term that was coined in 1784.
461
00:28:30,750 --> 00:28:33,252
Planetary nebulae are objects...
462
00:28:33,294 --> 00:28:36,505
that have nothing to do
with planets, as it turns out.
463
00:28:36,548 --> 00:28:38,632
They get their name
from William Herschel...
464
00:28:38,675 --> 00:28:42,636
who looked at a planetary nebula
for the first time through a telescope...
465
00:28:42,679 --> 00:28:45,305
saw that it was round,
greenish in color...
466
00:28:45,348 --> 00:28:48,016
and it reminded him
of the planet Uranus.
467
00:28:49,853 --> 00:28:52,938
The blue greens of oxygen
and reds of hydrogen...
468
00:28:52,981 --> 00:28:56,191
dominate true color photos
of planetary nebulas.
469
00:28:57,444 --> 00:28:59,820
The Ring Nebula
is a prime example.
470
00:29:00,905 --> 00:29:07,161
It is 2,300 light-years from Earth
and 1.3 light-years in diameter.
471
00:29:07,203 --> 00:29:10,581
It is considered a prototype
for planetary nebulas.
472
00:29:12,333 --> 00:29:14,001
But the shape
of the Ring Nebula...
473
00:29:14,043 --> 00:29:16,962
is simple compared
to other planetary nebulas.
474
00:29:18,298 --> 00:29:21,592
It's remarkable to realize
that displays like these...
475
00:29:21,634 --> 00:29:26,930
accompany the death of nearly
every star in the cosmos...
476
00:29:26,973 --> 00:29:31,185
including our own Sun
in about five billion years.
477
00:29:33,146 --> 00:29:36,482
The star swells up
near the end of its life.
478
00:29:36,524 --> 00:29:38,901
The Sun will fill half the sky.
479
00:29:39,444 --> 00:29:40,944
When the sun
is setting in the west...
480
00:29:40,987 --> 00:29:43,614
another part of it
will be rising in the east...
481
00:29:43,656 --> 00:29:45,657
and at noon,
the whole sky will be filled...
482
00:29:45,700 --> 00:29:50,746
with this bright red object,
baking us to porcelain.
483
00:29:52,457 --> 00:29:56,627
At this point, the inside of the star
becomes wildly unstable.
484
00:29:57,462 --> 00:29:59,254
it shutters, and it quakes...
485
00:29:59,297 --> 00:30:03,675
and at that point, the surface,
which is very loosely bound...
486
00:30:03,718 --> 00:30:05,552
can be tossed into space.
487
00:30:06,513 --> 00:30:09,515
Think of it as a process
of stellar sneezing.
488
00:30:11,643 --> 00:30:16,313
The outer envelope of gas expands
as the Sun shrinks from a red giant...
489
00:30:16,356 --> 00:30:18,482
to become a hot white dwarf.
490
00:30:18,525 --> 00:30:21,985
The dwarf's ultraviolet light
excites the surrounding gas...
491
00:30:22,028 --> 00:30:25,697
causing it to glow
just as in star-forming regions.
492
00:30:25,740 --> 00:30:30,536
The brilliant display will last for
thousands of years before fading away.
493
00:30:33,581 --> 00:30:38,126
Just what kind of cosmic picture the
Sun will paint at the end of its life...
494
00:30:38,169 --> 00:30:40,379
is nearly impossible to predict.
495
00:30:41,381 --> 00:30:43,590
But witness
the astounding variety...
496
00:30:43,633 --> 00:30:46,552
of planetary nebulas
throughout the galaxy.
497
00:30:46,594 --> 00:30:50,264
What makes each one
dazzlingly different?
498
00:30:50,306 --> 00:30:53,767
And what engines drive
their enigmatic shapes?
499
00:30:55,895 --> 00:31:00,816
There are an estimated 10,000
planetary nebulas in our galaxy...
500
00:31:01,693 --> 00:31:07,239
each one displaying the death
of a star in its own unique way.
501
00:31:08,408 --> 00:31:13,620
Although each planetary nebula
is generated by a single star system...
502
00:31:13,663 --> 00:31:17,875
their size in comparison
is immense.
503
00:31:17,917 --> 00:31:20,377
Planetary nebulas are huge.
504
00:31:20,420 --> 00:31:23,338
If I had the solar system
between my fingers...
505
00:31:23,381 --> 00:31:29,094
the planetary nebula would be
1,000 to 10,000 times larger in radius.
506
00:31:30,054 --> 00:31:33,098
And yet, because of their
great distance from Earth...
507
00:31:33,141 --> 00:31:38,312
most planetary nebulas appear
to us as tiny specks in the cosmos.
508
00:31:38,354 --> 00:31:44,651
The distance to the planetary nebula
NGC 2440 is 4,000 light-years.
509
00:31:44,694 --> 00:31:48,614
And although the nebula itself
is one full light-year across...
510
00:31:48,656 --> 00:31:51,033
its size,
when viewed from Earth...
511
00:31:51,075 --> 00:31:54,661
is only four percent
as wide as the full Moon.
512
00:31:54,704 --> 00:31:58,874
Only the most powerful telescopes
can see it in detail.
513
00:32:01,628 --> 00:32:06,840
A nebula as large as the Moon
in apparent size is the Helix Nebula.
514
00:32:06,883 --> 00:32:10,886
But it still requires a photo
time-exposure to be seen at all.
515
00:32:11,679 --> 00:32:17,643
Its stunning form has inspired
some people to call it the "Eye of God. "
516
00:32:17,685 --> 00:32:20,812
At about 450 light-years away...
517
00:32:20,855 --> 00:32:24,441
it is among the closest
planetary nebulas to Earth.
518
00:32:24,484 --> 00:32:28,111
As such, it has been
studied intensely.
519
00:32:28,154 --> 00:32:31,239
This photo
from the Hubble Space Telescope...
520
00:32:31,282 --> 00:32:35,494
is one of the most detailed
astronomical images ever made.
521
00:32:35,536 --> 00:32:37,871
Among the surprises it reveals...
522
00:32:37,914 --> 00:32:42,125
are strange spoke-like knots
inside the nebula.
523
00:32:42,168 --> 00:32:43,752
They call them cometary knots...
524
00:32:43,795 --> 00:32:47,089
thinking maybe they're originally
from old comets around this star...
525
00:32:47,131 --> 00:32:50,342
when, in fact, it's really
a natural interaction...
526
00:32:50,385 --> 00:32:52,469
of the starlight with the gas.
527
00:32:52,512 --> 00:32:55,347
As the starlight comes out,
it sort of shocks the gas...
528
00:32:55,390 --> 00:32:57,808
kind of like throwing
cold water on a hot fire...
529
00:32:57,850 --> 00:33:03,105
and it causes the gas
to sort of curl and fragment.
530
00:33:06,859 --> 00:33:11,697
The brilliant colors seen in photos
of planetary nebulas are deceiving.
531
00:33:11,739 --> 00:33:13,991
If a spaceship
were near the central star...
532
00:33:14,033 --> 00:33:16,243
of the Helix Nebula,
for instance...
533
00:33:16,285 --> 00:33:21,039
the glowing gas would be practically
invisible because it's so thin.
534
00:33:22,792 --> 00:33:26,086
Only by speeding to
the planetary nebula's outer reaches...
535
00:33:26,129 --> 00:33:27,963
would the view start to change.
536
00:33:28,715 --> 00:33:33,510
We would have to travel for
about a thousand solar system radii...
537
00:33:33,553 --> 00:33:36,513
before we began to see
the glow of the gases...
538
00:33:36,556 --> 00:33:38,473
in the planetary nebula itself.
539
00:33:38,516 --> 00:33:40,642
And these would look
a lot like the Aurora...
540
00:33:40,685 --> 00:33:42,394
that we see here on Earth.
541
00:33:42,437 --> 00:33:44,730
The colors would be beautiful.
542
00:33:44,772 --> 00:33:48,567
Then shortly after that, we would
finish flying through the nebula...
543
00:33:48,609 --> 00:33:50,986
and we would be out
in the depths of space.
544
00:33:51,904 --> 00:33:55,449
Looking back on the nebula,
the colors are more apparent.
545
00:33:55,491 --> 00:33:58,160
The gas is otherwise
too thin to be seen...
546
00:33:58,202 --> 00:34:01,204
unless we're looking
through its entire envelope...
547
00:34:01,247 --> 00:34:04,166
billions of miles thick,
as we are now.
548
00:34:05,126 --> 00:34:07,794
But even at this point,
we need help.
549
00:34:08,546 --> 00:34:12,507
Our eyes see
the expected hydrogen red...
550
00:34:12,550 --> 00:34:15,552
but more colors show up,
and the structure becomes clearer...
551
00:34:15,595 --> 00:34:18,930
if our spacecraft applies
the Hubble palette to our view.
552
00:34:20,641 --> 00:34:24,311
Still, our view of the nebula
is limited by our position.
553
00:34:24,854 --> 00:34:26,229
Just as we do from Earth...
554
00:34:26,272 --> 00:34:29,066
we're seeing it
from only one direction.
555
00:34:29,108 --> 00:34:31,568
It looks like an elongated ring.
556
00:34:31,611 --> 00:34:34,404
But our spacecraft
speeds around the nebula...
557
00:34:34,447 --> 00:34:38,241
and we realize that from another angle,
it looks very different.
558
00:34:38,951 --> 00:34:41,995
It is not a ring of gas,
or even a sphere...
559
00:34:42,038 --> 00:34:44,831
but two distinct
intersecting disks...
560
00:34:44,874 --> 00:34:48,210
possibly caused by
the central star discharging gas...
561
00:34:48,252 --> 00:34:50,879
in two separate phases
at different times...
562
00:34:50,922 --> 00:34:53,256
near the end
of its life cycle.
563
00:34:56,469 --> 00:34:59,721
The questions surrounding
the shapes of planetary nebulas...
564
00:34:59,764 --> 00:35:02,766
are among the most perplexing
in all of astronomy.
565
00:35:03,643 --> 00:35:07,604
Let's take a look at some
of the shapes of planetary nebulae.
566
00:35:07,647 --> 00:35:11,983
They range from round
like the Lemon Slice Nebula...
567
00:35:12,026 --> 00:35:16,696
to elliptical like the Spirograph Nebula
and many others...
568
00:35:16,739 --> 00:35:19,741
to extreme cases
like the Ant Nebula...
569
00:35:19,784 --> 00:35:23,286
and the Double Squid Nebula,
otherwise known as M2-9.
570
00:35:26,499 --> 00:35:28,917
Since a star starts out
as a sphere...
571
00:35:29,752 --> 00:35:31,545
you might expect its dying gas...
572
00:35:31,587 --> 00:35:35,549
to produce
a spherical planetary nebula.
573
00:35:35,591 --> 00:35:39,928
But, in fact, only ten percent
of planetary nebulas have this shape.
574
00:35:41,430 --> 00:35:44,266
Among the engines
behind more exotic forms...
575
00:35:44,308 --> 00:35:46,977
are the stellar winds
from different layers of gas...
576
00:35:47,019 --> 00:35:51,106
thrown out by the star
at different times in its death cycle...
577
00:35:51,149 --> 00:35:52,899
and at different speeds.
578
00:35:53,776 --> 00:35:56,486
And what you get is
an interacting set of winds...
579
00:35:56,529 --> 00:35:58,488
winds colliding with other winds
from the inside.
580
00:35:58,531 --> 00:36:01,992
That's a process
that sculpts the nebula...
581
00:36:02,034 --> 00:36:04,703
and helps to give it
its interesting shapes.
582
00:36:06,914 --> 00:36:09,207
The most intriguing
of the planetary nebulas...
583
00:36:09,250 --> 00:36:10,917
are those with bipolar shapes.
584
00:36:12,211 --> 00:36:14,921
Mysterious forces
within these strange objects...
585
00:36:14,964 --> 00:36:18,008
cause glowing gas
to shoot out in jets...
586
00:36:18,050 --> 00:36:22,387
reminiscent of the stellar jets from
stars in the process of being born.
587
00:36:23,472 --> 00:36:25,974
How could two
so similar phenomena...
588
00:36:26,017 --> 00:36:30,145
happen at both the beginning
and the end of stellar life?
589
00:36:30,188 --> 00:36:32,522
Jets are a ubiquitous
phenomena in astronomy.
590
00:36:32,565 --> 00:36:34,900
What all these jets
have in common...
591
00:36:34,942 --> 00:36:36,902
is the presence
of an accretion disk...
592
00:36:36,944 --> 00:36:38,737
which is rotating gas...
593
00:36:38,779 --> 00:36:41,364
magnetic fields
in the rotating gas...
594
00:36:41,407 --> 00:36:43,533
and as material flows
through the accretion disk...
595
00:36:43,576 --> 00:36:44,868
and loads on the field lines...
596
00:36:44,911 --> 00:36:46,536
it gets blown
back out into space.
597
00:36:47,914 --> 00:36:52,209
But a dying star doesn't have
a disk of material falling into it.
598
00:36:52,251 --> 00:36:55,670
That is, unless it's a part
of a binary pair...
599
00:36:55,713 --> 00:36:58,465
two stars orbiting
around each other.
600
00:36:58,507 --> 00:37:02,510
Binary pairs are very common
in the universe.
601
00:37:02,553 --> 00:37:05,222
As the two stars
rotate around each other...
602
00:37:05,264 --> 00:37:08,725
one of the stars
is giving up mass to the other.
603
00:37:08,768 --> 00:37:10,560
Material flows
from one star to the other...
604
00:37:10,603 --> 00:37:12,145
and you form an accretion disk.
605
00:37:13,356 --> 00:37:15,398
Magnetic fields appear
in that accretion disk...
606
00:37:15,441 --> 00:37:18,652
and material is blown off it
just like in the other cases as well.
607
00:37:22,323 --> 00:37:25,075
Planetary nebulas represent
the normal processes...
608
00:37:25,117 --> 00:37:27,285
of star death throughout space.
609
00:37:28,246 --> 00:37:30,664
But there are giant stars
in the universe...
610
00:37:30,706 --> 00:37:32,457
that are far from normal.
611
00:37:32,500 --> 00:37:35,377
They conclude their lives
in massive explosions...
612
00:37:35,419 --> 00:37:39,256
and, often, the nebulas left
behind are the only clues...
613
00:37:39,298 --> 00:37:42,634
to just how they met
their violent ends.
614
00:37:45,721 --> 00:37:50,308
In the year 1054,
a massive star blew up...
615
00:37:50,351 --> 00:37:54,145
6,300 light-years away
from the solar system.
616
00:37:55,481 --> 00:37:58,483
From the Earth,
it appeared as a new star...
617
00:37:58,526 --> 00:38:01,069
the most brilliant in the sky.
618
00:38:01,112 --> 00:38:03,238
Ten times brighter than Venus...
619
00:38:03,281 --> 00:38:06,783
it was visible
in broad daylight for 29 days.
620
00:38:07,827 --> 00:38:10,578
It was noted
by Chinese astronomers...
621
00:38:10,621 --> 00:38:13,290
and perhaps the Anasazi
of New Mexico...
622
00:38:13,332 --> 00:38:15,667
as seen in one
of their petroglyphs.
623
00:38:17,169 --> 00:38:20,130
It faded away almost
as quickly as it appeared...
624
00:38:20,172 --> 00:38:24,217
and today we can see it
only through telescopes.
625
00:38:24,260 --> 00:38:27,304
But what's left of it
is spectacular.
626
00:38:27,346 --> 00:38:31,308
A thousand years later,
we call it the Crab Nebula...
627
00:38:31,350 --> 00:38:36,313
one of a variety of nebulas
known as supernova remnants.
628
00:38:36,355 --> 00:38:42,319
Supernova remnants are essentially
the expanding debris clouds...
629
00:38:42,361 --> 00:38:46,990
from the stellar explosion
of a really massive star.
630
00:38:47,033 --> 00:38:51,202
It's the death explosion of
that massive star at the end of its life.
631
00:38:52,997 --> 00:38:56,541
Supernova remnants are something
like planetary nebulas...
632
00:38:56,584 --> 00:39:00,337
in that each results
from the death of a star.
633
00:39:00,379 --> 00:39:04,674
As a star first evolves
to become a planetary nebula...
634
00:39:04,717 --> 00:39:08,845
it ejects dense mass
from its surface very slowly.
635
00:39:08,888 --> 00:39:11,890
This is not an explosion,
it's just an ejection.
636
00:39:13,017 --> 00:39:16,478
A supernova is much simpler.
It's just an explosion.
637
00:39:17,772 --> 00:39:19,981
Everything happens in seconds.
638
00:39:21,567 --> 00:39:23,193
And the nebula
that we see around it...
639
00:39:23,235 --> 00:39:25,612
is the shrapnel
that still remains.
640
00:39:27,323 --> 00:39:30,408
The light show comes from
the explosion's shockwave...
641
00:39:30,451 --> 00:39:34,621
smashing into the surrounding
material and causing it to glow.
642
00:39:36,665 --> 00:39:39,000
The principle
was dramatically illustrated...
643
00:39:39,043 --> 00:39:41,920
as it actually happened
in 2004...
644
00:39:41,962 --> 00:39:45,256
when the Hubble Space Telescope
caught this shockwave...
645
00:39:45,299 --> 00:39:48,635
striking a ring of gas
in the remnant of a supernova...
646
00:39:48,677 --> 00:39:53,681
that exploded 160,000
light-years away in 1987.
647
00:39:55,267 --> 00:39:58,895
Closer to home, the Crab Nebula
remains the most famous...
648
00:39:58,938 --> 00:40:01,398
of all supernova remnants.
649
00:40:01,440 --> 00:40:04,651
Studied through telescopes
for 300 years...
650
00:40:04,693 --> 00:40:10,907
it contains a secret buried inside,
undiscovered until 1968.
651
00:40:10,950 --> 00:40:16,121
At the very center is a pulsar,
spinning at thirty times per second.
652
00:40:17,456 --> 00:40:20,083
A pulsar is
a spinning neutron star...
653
00:40:20,126 --> 00:40:24,879
so dense that one teaspoon of it
would weigh a billion tons.
654
00:40:25,798 --> 00:40:29,551
The one inside the Crab Nebula
is just eighteen miles across...
655
00:40:29,593 --> 00:40:31,678
and weighs more than our Sun.
656
00:40:31,720 --> 00:40:36,975
It's spinning fast, but losing energy
by gradually slowing down.
657
00:40:37,017 --> 00:40:40,395
And the energy of its rotation
is being transferred into the gas...
658
00:40:40,438 --> 00:40:44,357
and, in fact, much of
the radiation in that nebula...
659
00:40:44,400 --> 00:40:46,985
is powered by the slowdown
of the pulsar.
660
00:40:48,362 --> 00:40:51,489
That radiation is seen
as the eerie blue glow...
661
00:40:51,532 --> 00:40:53,658
in the center
of the Crab Nebula.
662
00:40:53,701 --> 00:40:57,495
It is generated by electrons
moving at near the speed of light...
663
00:40:57,538 --> 00:40:59,998
through the magnetic fields
of the pulsar.
664
00:41:00,040 --> 00:41:02,333
But there is more
than blue glow.
665
00:41:02,376 --> 00:41:05,253
Recent space photos reveal
that the magnetic fields...
666
00:41:05,296 --> 00:41:08,131
are stirring up
the center of the nebula.
667
00:41:08,174 --> 00:41:11,176
You see little ripples
emanating out from the pulsar.
668
00:41:11,844 --> 00:41:13,303
It's not a bad analogy...
669
00:41:13,345 --> 00:41:15,930
to think of magnetic fields
as stretched rubber bands...
670
00:41:15,973 --> 00:41:16,973
and when you pluck them...
671
00:41:17,016 --> 00:41:20,101
you cause a disturbance
that works its way through them.
672
00:41:20,144 --> 00:41:22,228
And that's what's going
on somehow or another.
673
00:41:22,271 --> 00:41:24,314
The details are beyond us.
674
00:41:25,024 --> 00:41:28,359
But we can see the phenomenon,
and it's quite clear.
675
00:41:30,488 --> 00:41:33,156
The death of the star
that formed the Crab Nebula...
676
00:41:33,199 --> 00:41:36,201
is part of the life cycle
of the galaxy.
677
00:41:37,286 --> 00:41:38,870
The gas expelled into space...
678
00:41:38,913 --> 00:41:42,081
as supernova remnants
and planetary nebulas...
679
00:41:42,124 --> 00:41:44,000
returns
to the interstellar medium...
680
00:41:44,043 --> 00:41:48,087
where it becomes raw material
for future generations of stars.
681
00:41:49,215 --> 00:41:51,716
This process
cannot go on forever...
682
00:41:51,759 --> 00:41:55,053
because we have a finite
amount of hydrogen gas.
683
00:41:55,679 --> 00:41:59,015
Sooner or later, you use up
most of the hydrogen and helium...
684
00:41:59,058 --> 00:42:02,894
which light up the stars,
and the stars blink out.
685
00:42:06,148 --> 00:42:08,483
When you look
at the Milky Way today...
686
00:42:08,526 --> 00:42:12,153
ninety-seven percent
of its mass is in stars...
687
00:42:12,196 --> 00:42:15,156
three percent is left in gas.
688
00:42:15,199 --> 00:42:17,367
And as star formation proceeds...
689
00:42:17,409 --> 00:42:20,203
that reservoir is going to go
down and down and down.
690
00:42:20,246 --> 00:42:24,207
Certainly, star formation
will slow down because this gas...
691
00:42:24,250 --> 00:42:26,793
is just harder to get out
of the ground, as it were.
692
00:42:29,421 --> 00:42:32,382
But astronomers, using
the Green Bank Radio Telescope...
693
00:42:32,424 --> 00:42:35,051
have recently discovered
one source of gas...
694
00:42:35,094 --> 00:42:38,179
in a massive cloud
outside the Milky Way.
695
00:42:41,100 --> 00:42:42,809
The very interesting thing
about this cloud...
696
00:42:42,851 --> 00:42:44,477
which has been
called Smith's Cloud...
697
00:42:44,520 --> 00:42:46,062
is that it's very massive.
698
00:42:46,105 --> 00:42:50,358
It's got about a million times the mass
of the Sun in it of gas and dust.
699
00:42:50,401 --> 00:42:52,819
Well, this cloud is headed
right toward the Milky Way.
700
00:42:52,861 --> 00:42:56,197
And in 20 to 40 million years,
it's going to collide with us.
701
00:42:57,449 --> 00:43:00,702
Now, that's going to create
a pressure, a shockwave.
702
00:43:00,744 --> 00:43:04,581
And it may set off a generation
of hundreds of new stars...
703
00:43:04,623 --> 00:43:06,124
when it collides
with the Milky Way.
704
00:43:08,252 --> 00:43:11,838
As the gas in Smith's Cloud
is compressed by the collision...
705
00:43:11,880 --> 00:43:16,217
a brand-new star-forming nebula
will light up the galaxy...
706
00:43:16,260 --> 00:43:19,470
and the lifecycle
of the universe will continue.
707
00:43:22,433 --> 00:43:25,852
In the long term, however, there
aren't enough Smith's Clouds...
708
00:43:25,894 --> 00:43:27,937
to keep the process going...
709
00:43:27,980 --> 00:43:30,982
and nebulas
will gradually disappear.
710
00:43:32,526 --> 00:43:35,361
The universe is about
14 billion years old...
711
00:43:35,404 --> 00:43:37,113
and come back
in a hundred billion years...
712
00:43:37,156 --> 00:43:38,990
and look at the Milky Way...
713
00:43:39,033 --> 00:43:42,160
the big, bright, massive stars
can't form anymore.
714
00:43:43,537 --> 00:43:46,456
All that's left are
the ancient remnants of stars...
715
00:43:46,498 --> 00:43:48,499
that formed in the long past.
716
00:43:49,293 --> 00:43:52,545
It's a dull place,
a very dull place.
717
00:43:52,588 --> 00:43:56,132
We live in an exciting time
in the era of the universe...
718
00:43:56,175 --> 00:43:58,384
before stars burn out...
719
00:43:58,427 --> 00:44:00,887
and the reservoir
of new material is gone...
720
00:44:00,929 --> 00:44:03,681
for forming
new stars and planets.
721
00:44:03,724 --> 00:44:05,266
It's a privileged time.
722
00:44:06,727 --> 00:44:09,937
A time when the sky
still remains filled...
723
00:44:09,980 --> 00:44:12,690
with the lights
of the great Orion Nebula...
724
00:44:12,733 --> 00:44:14,692
the Pillars of Creation...
725
00:44:14,735 --> 00:44:16,986
and the Eye of God...
726
00:44:17,029 --> 00:44:19,822
each one
a small marvel of nature...
727
00:44:19,865 --> 00:44:24,202
in the vast expanse
of the universe.
62994
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