1. Universe and Galaxies
Earth Science
2014
Pulford

2. Astronomers define the universe as all of space and everything in it.

3. Galaxies
A galaxy is a huge group of single stars, star systems, star clusters, dust, and gas bound together by gravity.
There are billions of galaxies in the universe.
The largest galaxies have more than a trillion stars.

4. Astronomers classify most galaxies into the following types:
Spiral
Elliptical
Irregular

5. Spiral Galaxy

6. Elliptical

7. Irregular

8. Our Galaxy The Milky Way
Our solar system is located in a spiral galaxy called the Milky Way.
From the side, the Milky Way would look like a narrow disk with a large bulge in the middle.
But from the top view, the Milky Way would have a spiral, pinwheel shape.

9. Milky Way-Side View
Sun’s location

10. Milky Way-Top View
Sun s location

11. The BIG BANG Accepted theory about how the universe was created
About 13.7 billion years ago, the universe was no larger than the period at the end of this sentence.
This tiny universe was incredibly hot and dense.
The universe then exploded in what astronomers call the big bang.

12. Scientific Proof behind the Big Bang Theory
Edwin Hubble was able to study other galaxies and see if the were moving towards us or away from us
He could also tell us how fast they were moving (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. Hubble’s law strongly supports the big bang theory.

13. Scientific Proof behind the Big Bang Theory
Cosmic Background Radiation
In 1965, two American physicists accidentally detected faint radiation on their telescope.
This mysterious glow was coming from all directions in space.
Scientists later concluded that this glow is the leftover heat energy from the big bang.
This energy was distributed in every direction as the universe expanded.

14. Graphic Organizer
Evidence
THEORY

16. Stars
Stars are classified according to their color, temperature, size, composition, and brightness.
Color: determined by the temperature
(coolest) Red  Red-Orange  Yellow  White Blue (hottest)
0C , ,000
Size: Even though they all appear the same to us, they can be very different
Composition: Helium, Hydrogen, Sodium, Calcium
Brightness: depends on its size and temperature
Apparent Brightness: Brightness as seen from Earth
Absolute Brightness: Brightness of the star if we were all at equal distances to every star

17. The Hertzsprung-Russell Diagram