1. Galaxies
Your complete address is part of a much larger system than your street, city, state, country, and even the planet Earth.

2. . . . You also live in the Milky Way Galaxy.

3. Galaxies Are large groups of stars, dust, and gas
Come in a variety of shapes and sizes
Large galaxies contain more than a trillion stars!
Hubble Space Telescope has helped us understand the different types of galaxies
Are classified by their different shapes

5. Spiral Galaxies Have a bulge at the center Have spiral arms
Arms made up of gas, dust, and new stars
Examples: Andromeda and our Milky Way Galaxy

6. Interesting Facts!
Earth is about two-thirds of the distance from the center of the Milky Way to the edge of the Milky Way.

7. Interesting Facts!
Our solar system revolves around the galaxy every 200 million years.

8. Interesting Facts!
The last time the solar system was in its current position was during the Triassic period, when dinosaurs first appeared on Earth!

9. Other Spiral Galaxies

10. Barred Galaxies Much like spiral galaxies
Have two distinct “bars” vs. many spiral arms

11. Other Barred Galaxies

12. Elliptical Galaxies About 1/3rd of all galaxies
Simply a massive blob of stars
Spherical or more stretched out
Very bright centers with little extra gas and dust
Contain mostly old stars

13. Lenticular Galaxies Has both a bulge and a disk
All the stars are thought to be old
Have no spiral arms
There is little or no gas

14. Irregular Galaxies Don’t tend to fit into any other class
Irregular shape
No center bulge
May have been formed by the collision of two or more galaxies
Many are close in proximity to large spiral galaxies. Perhaps the spiral galaxies are distorting the shape of irregular galaxies.

15. What are Galaxies Composed of?
Billions of stars
Some planetary systems
Gas clouds
Star clusters

16. Nebula A large cloud of dust and gas in interstellar space
A region in space where stars are born or where stars explode at the end of their lives
Spiral galaxies usually have nebula, but elliptical galaxies contain very few.

17. Eagle Nebula
Scientists believe that stars are being born in the pillars of this nebula

18. Other Nebula

19. Star Clusters
Globular Clusters = groups of older stars, looks like a ball, contains up to 1 million stars

20. Star Clusters
Open Clusters = a group of stars that are close together relative to surrounding stars
The Pleiades are an open cluster

21. Quasars Starlike Are very luminous (bright) Generate a lot of energy
May be caused by massive black holes in the cores of some galaxies
Thought to be the most distant objects in the universe; 6 billion light-years away!

22. Origin of Galaxies
How is looking through a telescope like looking back in time?
Looking at distant galaxies reveals what early galaxies may have looked like.

23. Summary The universe consists of billions of galaxies
Galaxies are classified by shape
The Milky Way galaxy is a spiral galaxy
Studying galaxies helps scientists understand the origin on our galaxy and the universe