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.