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

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

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

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

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 http://worldsciencefestival.com/videos/robert_woodrow_wilson_big_bang

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

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

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

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

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

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

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

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

Chapter 15 Section 5 Homework – pg 627

1A. What was the big bang?

1B. When did the big bang occur?

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

2A. How old is the solar system?

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

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

3A. What is dark matter?

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

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