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UNIT NINE: Matter and Motion
in the Universe
 Chapter 26 The Solar System
 Chapter 27 Stars
 Chapter 28 Exploring the Universe
Chapter Twenty-Eight:
Exploring the Universe
 28.1 Tools of Astronomers
 28.2 Galaxies
 28.3 Theories about the Universe
Section 28.3 Learning Goals
 Explore theories about the origin of the
universe.
 Discuss the evidence in support of the Big
Bang theory.
 Describe planetary systems.
28.3 Doppler Shift
 In the 1800s, Christian
Doppler discovered that
when the source of a
sound wave is moving, its
frequency changes.
 The change in sound you
hear is caused by a
Doppler shift.
 Doppler shift is related to
the net change between the
source of the waves and
the observer.
28.3 Doppler Shift
 Doppler shift also
occurs with
electromagnetic
waves, such as
visible light, X-rays,
and microwaves.
 This phenomenon is
an important tool
used by astronomers
to study the motion
of objects in space.
28.3 The expanding universe

The faster the source
of light is moving
away from the
observer, the greater
the redshift.

The opposite
(blueshift) happens
when an object is
moving toward the
observer.
28.3 The expanding universe

Edwin Hubble
discovered that the
farther away a galaxy
was, the faster it was
moving away from
Earth.

This concept came to
be known as the
expanding universe.
28.3 The Big Bang theory

The theory that the universe was
expanding implies the universe must have
been smaller in the past than it is today.

It implies that the universe must have had a
beginning.

Astronomers today believe the universe
exploded outward from a single point.

This idea is known as the Big Bang theory.
28.3 The Big Bang theory

The Big Bang theory says the
universe began as a huge explosion
between 10 billion and 20 billion years
ago.

According to this theory, all matter
and energy started in a space smaller
than the nucleus of an atom.
28.3 Evidence for the Big Bang theory

In the 1960s, Arno Penzias
and Robert Wilson were
trying to measure
electromagnetic waves
given off by the Milky
Way.

The “noise” these
scientists found was the
cosmic microwave
background radiation
predicted by the Big Bang
theory.
28.3 Evidence for the Big Bang theory

The proportion of hydrogen to helium is
consistent with the physics of the Big Bang.

If the universe were significantly older, there
would be more heavy elements present
compared with hydrogen and helium.
28.3 Planetary systems
 A star with orbiting planets is called a
planetary system.
 Scientists now believe that planets are a
natural by-product of the formation of stars.
28.3 How the solar system formed
 Scientists think that the solar system was
formed out of the same nebula that created the
Sun.
28.3 Binary stars
 A binary star is a
system with two stars
that are gravitationally
tied and orbit each
other.
 About half of the 60
nearest stars are in
binary (or multiple)
star systems.
Optional* Investigation 28C
The Time Machine
 Key Question:
How long does it take for starlight to reach Earth?
Searching the Cosmos
 Astrophysicist Dr. Hakeem
Oluseyi (Oh-lu-SHAY-ee) is
fascinated by stars. A
physics and space science
professor at the Florida
Institute of Technology, he
has invented several new
instruments to give
astronomers a closer look at
the cosmos.