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Galaxies, Nebulae,
and Stars
TEKS 8.8A describe components of the
universe including stars, nebulae and
galaxies, and use models such as the
Herztsprung-Russell diagram for
classification
TEKS 8.8B recognize that the Sun is a
medium-sized star near the edge of a
disc-shaped galaxy of stars and that
the Sun is many thousands of times
closer to the Earth than any other star
We live in a galaxy
called the Milky Way.
A galaxy is a system
of stars, planets gas,
dust and dark matter.
Within galaxies are star
forming regions called
nebula. A nebula is a
cloud of dust, hydrogen
and helium gases.
It is in these clouds
of gas and dust that
stars sometimes
form.
A star is a
large ball of
gases that
generates
its own
energy
through
nuclear
fusion.
Fusion is a
process in
which
hydrogen
and helium
fuse to form
heavier
elements.
This process
generates
large
quantities of
energy.
The energy
is emitted
from the
star in the
form of heat
and light.
Stars
undergo
many
changes
through
their
evolution.
Depending on the
mass of the star, its
lifetime may be a few
million years to
trillions of years.
Lower massed stars
can generate energy
for billions of years.
Stars that are very
massive generate
energy for only a few
million years.
Stellar Evolution
Nebula with
protostars
Over the
course of
the star’s
evolution
the energy
generated
by the star
begins to
decrease.
Ultimately,
the star will
no longer
have
enough
hydrogen
or helium
to continue
to radiate.
Our Sun is only one of
many stars in the
universe.
It is
considered
to be a
mediumsized star
near the
edge of our
disc-shaped
galaxy.
So what will
happen to our Sun?
At the end
of the
sun’s life,
it will
gradually
brighten,
as it has
been doing
for the last
4 billion
years.
Around
5,000,000,
000 AD,
the
hydrogen
in the
Sun’s core
will run
out.
The sun
will
expand
into a red
giant
about
three
times
larger
than it is
now.
The increased
brightness will boil the
oceans and raise our
temperatures to over
1000 Kelvin.
Eventually,
the Sun will
shrink, but
then expand
again,
charring the
surface of the
earth with solar
prominences.
If earth isn’t
destroyed, it will
become a cold, dark
chunk of rock
circling a white
dwarf.