1. Galaxies
Chapter 15-3 pp

2. What are Galaxies? Galaxies are large groupings of stars in space.
Galaxies also contain gas clouds and dust
Galaxies come in a variety of sizes and shapes.

3. Spiral Galaxies
Spiral galaxies have a bulge at the center and very distinctive spiral arms.

4. The Milky Way
From earth, we see our galaxy as a bright band of stars that cuts across the night sky.
200 billion stars including the sun.
Our sun is located about two-thirds of the way between the center of the galaxy and its edge.

5. Elliptical Galaxies Round or oval in shape Up to 5 trillion stars
Very bright centers
Very little dust or gas
No new stars forming
Contain only old stars

6. Irregular Galaxies Have no definite shape
Some form when galaxies collide

7. Contents of Galaxies
Globular cluster – highly concentrated group of stars
Nebula – cloud of gas and dust where stars are born
Open cluster – group of 100 – 1000 stars that are close together relative to other stars.

8. Quasars Most distant objects in our universe
Star-like sources of energy located in the centers of galaxies
May be caused by super massive black holes in the cores of galaxies
Power of 10 trillion suns

9. Origins of Galaxies
Because light takes time to travel through space, looking through a telescope is like looking back in time. (Sunlight that falls on the Earth is 8.3 minutes old)
Looking at distant galaxies reveals what early galaxies looked like.
This information gives
scientists ideas about
how galaxies form and
how galaxies change over
time.