Download STARS

Please pick up the TWO STARS packets from the
back and sit down. Fill in the upper right and
READ through the fill in the blank notes sheet to
see what you know. We will begin our notes
shortly
STARS
What are stars?
1-23-08
Stars are self-luminous spheres. Self
luminous means that stars generate
their own light.
 This
makes stars different from
planets, moons, asteroids, and
comets, all of which shine by
REFLECTING light.
Stars are different in other ways:
 They
possess far more mass (stuff).
 They have different compositions.
 They are hotter.
 Most are bigger that planetary objects
Lets use the sun, our nearest star as an
example. It is a self luminous, gaseous
sphere. It has no solid surface. Its size is
about 100 times the Earth and its mass is
about 300,000 times that of the Earth. Its
core temperature is 27 million degrees
Fahrenheit and its visible surface is 10,000
degrees Fahrenheit. The Sun is made up
of mostly hydrogen and helium. The
heavier elements carbon, oxygen,
nitrogen, iron, and gold make up only
about 2% of the Sun’s mass.
The Sun’s luminosity, its brightness –
referred to as one solar luminosity. This is
comparable to 4 trillion one-hundred-watt
light bulbs
Our Sun is rather average. Some
stars are bigger, more massive,
and brighter. Others are smaller,
less massive, and less bright.
Some stars are single like the Sun.
Others have one or several
companion stars. Some stars are
much older than the Sun. Others
have been formed very recently.
Interesting Fact
The Earth intercepts about one-half
billionth of the energy radiated by the
Sun. If we could harness all of the
energy the sun radiates in one
second, we’d have enough energy to
satisfy the current US energy
consumption for about 4 million years.
What makes a star shine?
Stars are nuclear furnaces. Stars
generate their own energy by nuclear
reactions in their super hot cores.
This newly released energy flows from
the stars’ hot interiors to the cooler
surface layers, where the energy is
radiated into space. We see that
radiation and say the stars shine.
Back to the sun as our example. The
temperature is so hot in the core of
the Sun that hydrogen atoms fuse
into helium atoms with the release of
large amounts of energy. It is the
same process that powers a hydrogen
bomb explosion, the difference is that
the sun is not explosive and goes on
at a steady pace for billions of years.
Most stars you see in the night
sky get their energy in this way.
Eventually the hydrogen core
will become a helium core. The
helium core will then fuse into
carbon and oxygen, with still
more energy being released.
Do stars shine forever?
Stars do not shine forever. Stars
are of finite size. That means
that stars have only a certain
amount of nuclear fuel.
Eventually they will use up all
their fuel and fade.
How long stars shine depends on
how much mass the have.
Mass determines the amount of
fuel stars have at birth. Mass
also determines how bright
stars are, or how rapidly they
consume fuel
The greater a stars mass, the greater is
the amount of its nuclear fuel.
However, the more massive stars are
fuel guzzlers. They shine much
brighter than less massive stars and
use up their fuel very fast. So the
more massive stars have shorter lives.
Our sun will last about 10 billion years (
we are currently about 5 billion years
into that life).
Why are stars important to us?
The Sun (our nearest star) gives us light
and warmth.
2. The Earth was formed as a by product of
the formation of the Sun
Our planet and other planets in the solar
system came into existences as byproducts of the formation of t he sun.
Without the Sun, there would be no Earth,
and no life, as we know it.
1.
3. Carbon, Nitrogen, Oxygen and other
elements needed for life were produced
by earlier generations of stars.
Nearly all of the elements heavier than
hydrogen and helium in today’s universe
were manufactured in earlier generations
of stars. The most massive of those stars
ended in a super-energetic explosions,
called supernovae, ejecting their heavy
elements into space
Some 4.6 billion years ago, our sun and the
planets formed from clouds of gas and
dust enriched by heavy elements from
earlier generation of massive stars.
Stars Lab Homework
 Plot
the 16 stars on the H-R Diagram
 Define the 12 vocabulary words on
the back of your NOTES packet.