1. Section 5 – pg 622 The Expanding Universe
Chapter 15
Section 5 – pg 622
The Expanding Universe

2. Pg 622
The Andromeda Galaxy is the most distant object that can be seen w/ the human eye
It is 3 million light-years away

3. How the Universe Formed
Pg 622
How the Universe Formed
Astronomers theorize that the universe began billions of years ago
The beginning universe was very small, hot and dense
Universe exploded in the big bang
Since then the universe has been increasing in size
As it expanded, it cooled
Eventually atoms formed
Gravity caused stars and
galaxies to form

4. Pg 623
Moving Galaxies
In 1920s Edwin Hubble studied the spectrums of many galaxies at various distances from Earth
Could tell how fast the galaxy is moving and if it is moving towards or away from us
Discovered that most galaxies are moving away from us
Hubble’s law states that the farther away a galaxy is, the faster it is moving away from us
Supports the big bang theory

5. Cosmic Background Radiation
Pg 624
Cosmic Background Radiation
1965, 2 American physicists, Arno Penzias & Robert Wilson, accidently detected faint radiation on their radio telescope
Was coming from all directions in space
Cosmic Background Radiation: the leftover thermal energy from the big bang
Distributed in every direction as the universe expands

6. Pg 624
Age of the Universe
Since we can measure how fast it is expanding, we can calculate how long it has been expanding
Estimate that the universe is abt 13.7 billion years old

7. Formation of the Solar System: The Solar Nebula
Pg 625
Formation of the Solar System: The Solar Nebula
Abt 5 billion years ago, a giant cloud of gas & dust collapsed to form our solar system
Solar Nebula: large cloud of gas and dust that form a solar system
Gravity pulls the solar nebula together, causing it to spin and flatten into a disk until the gas eventually becomes hot and dense enough to start nuclear fusion

8. Pg 625
Planetesimals
In the outer parts of the disk, gas and dust formed asteroid-like and comet-like bodies called planetesimals
Collided and stuck together to form planets

9. Pg 625
The Planets
When the solar system was forming, it was hot close to the sun
All water vaporized and gases escaped the small planets forming there
It was cooler where the farther out planets were forming
As they grew, their gravity was able to capture the gases in the region making the planets bigger

10. Evidence Evidence for solar nebula theory Pg 625
Composition of inner and outer planets
Position of sun at the center and planets revolving

11. The Future of the Universe
Pg 626
The Future of the Universe
Possibly, the universe will continue to expand, and the stars will all eventually go out OR
Gravity will begin to pull the galaxies back together
All matter in the universe will
be crushed into an enormous
black hole

12. Pg 626
Dark Matter
Astronomers use to think that the universe was made of matter that could be observed directly
American astronomer Vera Rubin made detailed observations of the rotation of spiral galaxies
Matter that can be seen only made up 10% of the mass, the rest is dark matter
Dark Matter: matter that does not give off electromagnetic radiation & cannot be seen directly
Presence can be inferred by observing the effect of its gravity on other objects

13. An Accelerating Expansion
Pg 626
An Accelerating Expansion
Dark Energy: mysterious force that might be responsible to the universe expansion

14. Chapter 15 Section 5 Homework – pg 627

15. 1A. What was the big bang?

16. 1B. When did the big bang occur?

17. 1C. Describe two pieces of evidence that support the big bang theory.

18. 2A. How old is the solar system?

19. 2B. What force caused the solar system to form?

20. 2C. Place the following events in the proper order: planetesimals form; solar nebula shrinks; nuclear fusion begins in the sun.

21. 3A. What is dark matter?

22. 3B. How do scientists know that dark matter exists?

23. 3C. What evidence has led scientists to predict that the universe will continue to expand forever?