WEBVTT

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- Did you know that when you
look up in the dark night sky,

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you are, in a way,
looking back in time?

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It's really true.

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Much of the light you see
coming from the stars

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has been travelling across
space for thousands of years

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by the time it reaches us
here on Earth.

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Some of those stars that you can
see tonight in the night sky

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may have burned out
millions of years ago.

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If you have ever wondered
where stars come from,

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how they change,
and what happens to them

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when their life
comes to an end,

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hang with me for a few minutes
as this episode

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of "NASA Launchpad"
takes a closer look

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at the life cycle of stars,

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and bonus, we are going to talk
a little bit about how

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each of us is actually
made from dead stars.

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Yeah, really.

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[upbeat electronic music]

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- Lift off.

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[upbeat electronic music]

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- Most things in the universe
have a life cycle.

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Thankfully for some things,
like these guys,

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the life cycle
is incredibly short.

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But for other things,
like stars,

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the life cycle
can be billions of years long.

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The life cycles for stars begin
in giant stellar nurseries

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called nebula.

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If you look at one of these
star-forming nebula,

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you will see beautiful
giant clouds of dust and gas.

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How a star forms
is a little technical,

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so let's hear an explanation
from an expert.

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- A star is basically
a nuclear furnace.

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It's this collection of
mostly hydrogen gas,

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and at the center it's really,
really hot and dense,

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where you can actually get
nuclear fusion occurring,

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and that's how you get the heat
and the light from the star.

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In space you have this
collection of sort of

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diffused gas and dust particles.

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It's just sort of everywhere
in space.

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Occasionally it comes
together through gravity.

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It's attracted to itself
basically,

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and so you get these
giant molecular clouds

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that are called
these big nebula.

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As that stuff comes together
through its own gravity,

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you eventually get these places
where you have enough material

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where you can start
to form a star,

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where it all comes together
and the gravity pushes on it

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so hard that it heats up
in the center,

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and that heating up
is what will eventually lead to

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fusion and the birth of a star.

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Two of the most important
properties of a star

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are its color
and its brightness.

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And so if you take stars and
you sort of sort them by color,

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you get anything from
red to blue,

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where the red stars
will be the cooler stars

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and the blue stars
will be the hotter stars,

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so that's really
a measure of temperature.

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And then you can also sort them
by their brightness,

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and so you have
the very bright stars,

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which are usually
the more massive stars,

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and the dimmer stars,
which are usually less massive.

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And just by
these two parameters,

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you can actually tell a lot
from a star.

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You can tell how massive it is.

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You can tell how big it is,
its radius.

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You can tell how old it is.

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You can know what stage
of evolution it's in,

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and you can learn about
the environment of the star--

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that the star was born in.

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- As you know,
our sun is a star.

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It is actually
a fairly modest sized star.

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It is believed that our sun
is about halfway through

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its 10-billion-year life cycle.

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Yes, that makes our sun about
5 billion years old.

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But don't worry.

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We're all good for at least
another 5 billion more years.

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So how will our sun's life cycle
play out?

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- So our sun is a low mass star,

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and it's actually gonna go
through a really long evolution.

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It's going to be in the phase
that it's currently in,

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where it's just fusing hydrogen
into helium,

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for about 10 billion years.

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And then once it runs out
of fuel in its center,

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it's going to evolve into
a red giant star,

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red meaning
that it's gonna be cooler,

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and it's gonna be so large
that its outer radius

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is actually gonna reach
the Earth's orbit.

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It's gonna be a huge star.

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And then eventually
it'll blow off its outer layers

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and become a white dwarf star,

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and that will be the--
its final phase.

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- So at the end
of a massive star's life,

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we have what's called
a core collapse super nova.

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So the core region collapses
in on itself

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and the outer region infalls
and then rebounds,

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and you get left with
a neutron star or a black hole.

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- You have may have noticed that
no matter the size of the star,

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at the end of its life cycle,
most of its material

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is expelled back into clouds
of dust and gas in the galaxy.

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The life cycle of a star
can begin again.

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- Throughout a star's life,
it's throwing off material,

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and this material
has been enriched

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by nuclear fusion reaction,

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so originally
really only hydrogen

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and a little bit of helium
was produced in the big bang,

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and all of the elements
that we get after that

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have been produced
in either a star's life

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or in its explosion if
it's massive enough to explode.

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And that material gets mixed in
with the other gasses and dust

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in the interstellar medium,

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and produces the next generation
of stars.

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So every generation of stars
that you produce

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is more and more enriched
with material from the life

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and death of stars.

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- So what does all of this
mean for us?

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And what is our connection
to the cosmos?

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- All of that fusion
that's going on in the centers

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of stars is creating heavier
and heavier elements,

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and that's how you get basically
everything you see around you,

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from the carbon to the iron,
the oxygen, everything.

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You can't get any of those
elements without having a star

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forming it
in the first place.

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And so everything that your body
is made up,

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everything that you see
around you

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all came from the center
of a star.

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- Pretty amazing, isn't it?

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When you look at
that periodic table

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hanging in your science class,
it represents all of the natural

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and man-made elements.

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Most of those natural elements
were formed and fused

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inside of long-dead stars.

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Yeah, that's right.

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Everything around you,
including you and me,

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was formed from the remnants
of exploded stars

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and the birth of the universe.

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We may look and act
differently from each other,

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but we are all made up
of the same stuff.

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Want to find out more?

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You can learn more about stars
and their life cycles

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from these NASA websites.

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That's it for now.

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See you next time
on "NASA Launchpad."

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[upbeat electronic music]