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Earth
Science
Unit 9: Our Place in the
Universe
Lessons 2 and 3: The Universe and
Our Galaxy
Make sure to have your study guide and a pencil
and be ready to go when the timer dings!
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and to the republic
for which it stands,
one nation under God,
indivisible, with liberty
and justice for all.
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Student Expectations…
Being part of this “school” is awesome! How can YOU make this ocean even more
awesome??.
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I will BE HERE! respond when my name is called, use polling
tools , complete classwork, notes, and chat to participate!
I will choose my attitude!
I will demonstrate respect and follow directions for my
classmates and teachers to help make their day!
I will have fun learning!
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What you can expect from class
to understand the main features
of the Big Bang Theory and to understand
the theory of the origin of the solar system
Essential question:
How do scientists believe
the universe was formed?
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Expanding Universe
Scientists believe that the
universe is continuing to expand.
They use what is called the
Doppler Effect to determine the
motion of massive groups of
stars in space. Their observations
of light show that bodies in the
universe display a red shift,
meaning they are moving away
from us.
The Doppler Effect
One important observation scientists have made
about the universe has to do with light. A
wavelength is the distance between the crests of
two waves. A special phenomenon called the
Doppler effect explains how wavelengths of
light— and sound—change when the source is
in motion.
The Doppler Effect: An Example
Remember a time when you have been near a
busy road and you hear the truck pass by. You
may have noticed that the sound is high coming
toward you and low going away. The sound’s
wavelength changes because the source of the
sound—the truck—is moving.
Doppler Effect
The Doppler effect works the same way with light. It
explains how a star’s motion affects light coming from it.
A star moving toward earth emits light in waves and
when the star is closer, the waves shorten. On a
spectrograph, shorter light waves appears bluer.
A star moving away emits each wave farther, stretching
them. Longer waves are redder. The shift's direction tells
whether a star is moving toward or away from us. The
shift's size tells us how fast it is moving.
Quick Check!
If a star is moving away from the earth, toward
which color will its visible light be shifted?
The Big Bang Theory
Astronomers concluded that if the universe is
expanding, it must have all been held together
in one spot at some point. Scientists infer that
the universe was once packed into a very small,
dense space that burst apart in an enormous
explosion called the "big bang." This is the big
bang theory of the origin of the universe.
The Big Bang Theory
As with other scientific theories, evidence
supports this idea. Besides the red shift of
distant stars, there is evidence of cosmic
background radiation. This glow, which can be
observed all over space, is the leftover energy
from the big bang. Working backwards,
scientists determine that the big bang occurred
about 14 billion years ago.
What happened?
Scientists have ideas about what happened in the very
early period of our universe.
• Early during the process, hydrogen formed and
combined to make some helium.
• Hydrogen and helium formed massive clouds from
which large stars formed.
• Other elements formed in large stars. Stars used up
their early fuel, and some larger ones exploded.
• These explosions formed large clouds of gas and dust.
• From such clouds, a solar system with a star, planets,
and other bodies of different sizes could form.
Quick Check!
According to the theory, what best describes the
universe before the big bang?
A. A star
B. A planet
C. A cloud of gas and dust
D. A densely packed space
Quick Check!
Which of the following is used as evidence that
the universe began with the big bang?
A. Craters on the moon
B. Leftover energy in the universe from the
event
C. The force of gravity
D. The existence of atoms
The Big Crunch??
Some scientists suggest that the expanding universe has a
limit and that one day the universe will begin to contract.
It may then produce a “big crunch,” forming another
original point that will produce yet another big bang. For
this to happen, there must be enough matter in the
universe to create the gravitational force that pulls it back
together.
However, observations show that the universe is
expanding at a fast-paced rate. Astronomers explain this
puzzling observation with an idea about a new force,
which they refer to as “dark energy.” Most of the universe
appears to be made of dark matter and dark energy.
20
Light-Year
There is a lot of space in space.
Stars are very far apart.
Distances in space are so large
that it makes calculations using
ordinary units of measurement,
such as miles, impractical. As a
result, scientists defined a unit
of measure, called the light-year,
to determine distances in space.
A light-year is the distance light
travels through space in one
earth year. Light travels through
space at a speed of 186,000
miles per second.
Galaxies
When you go outside on a clear night, you
can see lots of stars. On a very clear night in
a dark area, you may even be able to see a
fuzzy white band that crosses the sky. This
fuzzy band is our galaxy, the Milky Way.
Galaxies are huge clusters of these stars, gas,
and dust that are bound by the forces of
gravity. Galaxies can contain billions of stars
and are quite massive in size! For example,
Andromeda, a nearby galaxy similar to the
Milky Way, measures an astounding
1,290,000,000,000,000,000 (1,290 billion
billion) miles across!
Quick Check!
Which number best describes the number of
starts you would find in a galaxy?
A. Hundreds
B. Thousands
C. Millions
D. Billions
The Shape of Galaxies
There are billions of galaxies in the universe and
each one is unique. Galaxies have different ages,
sizes, and distances from earth. Astronomers
classify galaxies by shape: spiral, elliptical, and
irregular.
Spiral Galaxies
Spiral galaxies get their name for their arms
of gas, dust, and stars that spiral out from a
densely packed cluster of stars in the center.
Spiral galaxies typically have a mix of stars,
some young and some old.
The Milky Way is a special type of spiral
galaxy, called a barred spiral. Barred-spiral
galaxies have a thick bar of stars and gas
passing through their centers. From earth,
the fuzzy white band that is the Milky Way
doesn’t look like a spiral; it looks like a stripe.
That is because we are looking at the Milky
Way sideways, from inside one of its spiral
arms.
Elliptical and Irregular Galaxies
The two other major kinds of galaxies are elliptical and irregular.
An elliptical galaxy has a shape like a
stretched circle, or oval. Elliptical galaxies
usually have only old stars. This is because
they contain little gas or dust.
As their name suggests, irregular galaxies
have no distinct or orderly shape. Many
new stars are born in irregular galaxies. This
is because these galaxies contain far more
gas and dust than elliptical or spiral
galaxies.
Quick Check!
What category of galaxy does not have a
distinctive shape?
A. Spiral
B. Elliptical
C. Barred Spiral
D. Irregular
Galaxy Clusters
The universe contains billions—
perhaps trillions—of galaxies. Quite
often, galaxies are grouped together
in what astronomers call galaxy
clusters. A galaxy cluster may
contain only a few galaxies or as
many as thousands of galaxies.
Galaxy clusters occur in bunches
throughout space. This means that
there may be hundreds of galaxy
clusters in one region of space and
almost none in another region of
space.
Spinning Galaxies
Along with expanding, galaxies move in other
ways, too. For example, spiral galaxies spin fast
in the center, while their arms spin slower. Many
scientists think that several, or perhaps most,
galaxies rotate around the enormous
gravitational pull of a massive black hole at their
center.
Interstellar Material
The vast spaces between stars are not completely empty.
In most galaxies, the space between stars contains dust
and gases. These are called interstellar dust and gas
(“inter” means between).
Many scientists analyze dark matter that exists within
galaxies and perhaps even between galaxies. Dark matter
gets its name because it does not emit any radiation that
we can observe on earth.
No one knows for certain what dark matter really is or
what it does, but scientists do know that dark matter is
important in providing the gravitational force that holds
each galaxy together.
Quick Check!
What is a light-year?
A. The distance light travels in one earth year
B. The distance light travels from the sun to the
earth
C. The distance light travels in one orbit of the
mood
D. The time it takes light to travel across the
universe
Fun Science Fact!
All the individual stars that you can see
when you look at the sky at night without a
telescope belong to the Milky Way galaxy?
The ancient Greeks most likely saw galaxies
as milk-white wisps trailing over the night
sky, which is why they probably named the
Milky Way “Galaxies Kuklos” meaning the
Milky Circle.
Homework slide
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