ch. 21 stars, galaxies, and the universe€¦ · galaxies the milky way is the galaxy in which our...
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Stars, Galaxies, and the Universe
Star Systems and Galaxies
Identify and describe three types of
galaxies.
Galaxies
The Milky Way is the galaxy in which our solar system is located.
Looks milky or hazy because the stars are too close together for your eyes to see them individually.
There are billions of galaxies in the universe.
Astronomers have classified most galaxies into three main categories: spiral, elliptical and irregular.
Spiral Galaxies
A spiral galaxy is a
galaxy that has the
shape of twin
spirals. They have
arms that spiral
outward, like
pinwheels.
The Milky Way is a
spiral galaxy.
Elliptical Galaxies
Elliptical galaxies look,
like flattened ball.
They contain billions of
stars but have little gas
and dust. So they
cannot form new star.
They contain old stars.
Irregular Galaxies
Some galaxies do not
have regular shapes.
The Large Magellanic
Cloud is an irregular
galaxy about 160,000
light-years away from
our galaxy.
It is one of our closest
neighbors.
History of the Universe
Explain the big bang
theory of how the
universe was
formed.
Describe how the
solar system was
formed.
Introduction
Andromeda Galaxy
is the most distant
object you can see
with your unaided
eye. Light travels
for 2 million years
before reaching your
eye.
Moving Galaxies To study how and when the universe formed,
astronomers use information about how
galaxies are moving.
In the 1920’s, Edwin Hubble, an American
astronomer, discovered that the farther away
a galaxy is from us, the faster it is moving.
The Hubble Space Telescope was named
after Hubble in honor of these discoveries.
Raisin bread analogy- As the dough expands,
the raisins move farther apart. As the galaxies
expand, they move farther apart from one
another.
The Big Bang Theory According to the big bang theory, the
universe formed in an enormous explosion about 10 to 15 billion years ago. Since the big bang, the universe is billions of times larger than it was billions of years ago.
Astronomers have concluded that the galaxies are moving away from each other as a result of the big bang.
Astronomers estimate that the universe has been expanding for 10 billion to 15 billion years.
Formation of the Solar System
After the big bang, matter in the
universe separated into galaxies. Gas
and dust spread throughout space in
our galaxy.
About five billion years ago, a giant
cloud of gas and dust, or nebula,
collapsed to form the solar system.
Slowly the nebula shrank to form a spinning
disk. As gravity pulled some of the gas into
the center of the disk, the gas became hot
and dense enough for nuclear fusion to
begin. The sun was born. Gas and dust
formed solid spheres smaller than the sun.
The spheres closest to the sun lost most of
their gases and became the inner planets.
The spheres farthest from the sun
became the gas giants. Between the
inner and outer planets, asteroids
formed. Beyond the outer planets, a
huge cloud of ice and other substance
formed which is probably the main
source of comets.
The Future of the Universe
One possibility: The universe will continue to expand, as it is doing now. The stars will run out of fuel, burn out, and the universe will be cold and dark
Second possibility: The force of gravity will begin to pull the galaxies back together. A reverse “big bang”. The universe will be crushed into an enormous black hole.
It depends on the total mass of the universe
which is difficult to estimate because most of
it is in the form of particles that do not give off
electromagnetic radiation. The evidence so
far suggests that the total mass of the
universe is not great enough to pull the
galaxies back together again. More research
has to be done.
Astronomy is one of the oldest
sciences, but there are still many
discoveries to be made and puzzles to
be solved about this universe of ours.
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