1. Galaxies!
Out of this World

2. What is a Galaxy
Galaxy = made of billions of stars, dust, and gas all held together by gravity.
Galaxies are scattered throughout the Universe. They vary greatly in size and shape.
Not all galaxies look alike.

3. These are all galaxies

4. Did you notice that the galaxy pictures don't look alike?
In 1926, an astronomer named Edwin Hubble decided to classify the galaxies, grouping them according to their characteristics.
After considering different schemes, he decided to arrange or group the galaxies by shapes. He would classify them according to the way they looked.
Let's consider the three galaxies we just saw…

5. The first type of galaxy is an Elliptical galaxy.
1) Elliptical Galaxy = round galaxies "E" stands for elliptical galaxies.        
Hubble called the second type of galaxy a  spiral galaxy.
2) Spiral Galaxy = looks like a pinwheel or whirlpool. The letter "S" stands for spiral galaxies.        

6. Andromeda Galaxy

7. The third type of galaxy reminded Hubble of
3) a spiral galaxy with a solid bar across the center. = barred spiral galaxy. He used the letters "SB" to stand for barred spirals.
Many galaxies have strange, irregular shapes,
and do not fit neatly into any of these three categories.   

8. To show the relationship of the galactic shapes, Edwin Hubble arranged the main types of galaxies and the sub-types into a chart that has come to be called "The Tuning Fork Diagram".
The Tuning Fork Diagram is a way to classify Galaxies…

9. The Milky Way Galaxy – Our Home

10. The Milky Way – Our Home The Milky Way Galaxy is a Spiral Galaxy
But because we live within it, it is hard to tell exactly what it looks like
Contains 200 – 400 billion stars! (Remember our Sun is a star)
Our solar system is spiraling around 28,000 light years from the galactic center on the arm called the Local Arm

11. The Milky Way from Earth

13. Our closest neighboring galaxy
Andromeda Galaxy – 2.9 million light years away

14. What Is The Size of the Universe?

15. You have seen some pictures of galaxies in this lesson and have looked at how they were classified. Now it's time for you to classify some galaxy pictures. Are you up to the challenge?