1. Galaxies
and
the UNIVERSE

2. What is a galaxy?
A galaxy is a system containing millions or even billions of stars.
We estimate that there are 50 billion to 100 billion galaxies in the observable universe.

3. How are galaxies identified?
Galaxies are classified by shape.
Color is determined by the age of stars and the amount of dust.
SPIRAL
ELLIPTICAL
IRREGULAR

4. SPIRAL GALAXIES It has a nucleus with arms extending outward.
From the side they are lens shaped with a central bulge.
Examples are the Milky way and Andromeda galaxies.

5. The Milky Way Diameter = 100,000 light-years.
Sun is 26,000 light years from the center.
It belongs to a cluster of galaxies called the Local Group

6. The MThe Milky Wayilky Way

7. Elliptical Galaxies They range from nearly spherical to lens-shaped.
Stars are concentrated in the center.
They have very little stellar dust.
M87 is an example of an elliptical galaxy.

8. Irregular Galaxies These can be almost any shape.
Odd shaped galaxies are called Peculiar.
These are usually smaller than other galaxies.
The Large and Small Magellanic Clouds are examples.
The Cigar galaxy
Small Magallenic Cloud

9. New Ideas about Galaxies
Some galaxies may have a super massive black hole in the center.
Galaxies may be born in objects called QUASARS. These are extremely bright objects at the far edges of the universe.
                       
                                                          

10. What type of galaxies are these?
Ellipticall
Spiral
Irregular

11. What type of galaxies are these?
Spiral
Irregular
Irregular
Elliptical

12. How did the Universe begin?
The Big Bang Model is the most commonly accepted idea.
All matter was condensed into a dense sphere.
The sphere suddenly and quickly expanded outward.
The superhot and superdense universe continued to expand more slowly.
Temperatures gradually decreased.
Atoms began to form and material collected into clouds of gas.
These clouds became galaxies.
Eventually stars aged and planets formed.

13. Evidence for the Big Bang.
RED SHIFT
Cosmic Background Radiation
                            
Edwin Hubble discovered that all galaxies exhibit red shift. This indicates they are all still moving apart.
Penzias and Wilson discovered radiation apparently left over from the Big Bang Explosion. It was measured with a satellite called the Cosmic Background Explorer or COBE.

14. Red Shift of Galaxies
                
                
Receding Galaxy
Approaching Galaxy

15. Hubble Deep Field
Famous photo taken by the Hubble telescope when it was pointed at a single point in space.
It shows hundreds of galaxies in an area of space which is the size of Roosevelt’s eye on a dime held at arms length.

16. The Known Universe