1. Galaxies and the Universe
Notes
Galaxies and the Universe

2. The Milky Way
Galaxy: a huge group of stars, gas, and dust held together by gravity.
The Sun is part of the Milky Way galaxy.

3. The Milky Way Without a telescope, you only see nearby stars.
Nearby stars are a tiny fraction of the several hundred billion in the galaxy.

4. The Milky Way
The Milky Way is shaped like a disk with a bulge in the center.
Because our view is from inside the galaxy, all we can see of the Milky Way is one arm of stars across the sky.

5. The Milky Way The Milky Way is more than 100,000 light years across.
The Sun is about 28,000 light-years away from the center, which is a clump of densely packed stars.

6. The Milky Way
In addition to stars, the Milky Way contains clouds of gas and dust called nebulae (plural for nebula).
Heart nebula
Orion nebula
Carina nebula
NGC 3603

7. The Milky Way
The stars and nebulae orbit the center of the galaxy at high speeds.
The Sun takes about 250 million years to orbit the Milky Way galaxy once.

8. Galaxies
Galaxies range in size from a few hundred million stars to over a trillion stars.
Galaxies also have different shapes.

9. Arms of stars, gas, and dust curve away from the center
Disk-shaped with a central bulge
Composed of both old and young stars
Examples: Milky Way, Andromeda
Spiral Galaxies

10. Andromeda Galaxy

11. Grand Design Galaxy

12. Southern Pinwheel Galaxy

13. Elliptical Galaxies Shaped like spheres or eggs.
Very little dust and gas.
Made entirely of old stars.
Examples: IC 1101, M89

14. NGC 1132

15. M87

16. Irregular Galaxies Faint with no definite shape.
Smaller than other types.
Lots of gas and dust and many young stars.
Examples: the large and small Magellanic Clouds

17. Large Magellanic Cloud

18. Small Magellanic Cloud

19. Centers of Galaxies
Most large galaxies have supermassive black holes at the center.
These black holes have masses millions or billions of times greater than the Sun.

20. Centers of Galaxies
Supermassive black holes are so large that they often draw in huge whirlpools of gas from surrounding stars.

21. Centers of Galaxies
If the center of a galaxy is bright, it may look like a star from very far away.
Quasar: the bright center of a very distant galaxy.
The galaxy surrounding a quasar is often hard to see because the quasar is so bright.

22. The Universe
The Milky Way is one of at least 200 billion galaxies, though there are likely many more than that.
Galaxies occur in groups called superclusters.

23. The Universe
Between the superclusters are massive spaces of emptiness.

24. The Universe
The elements found in our solar system and galaxy are found throughout the universe.

25. The Universe
The same physical laws that govern our solar system and galaxy are also true throughout the universe.

26. Motion of Galaxies
Have you ever noticed that the sound of a siren changes as it travels toward and then away from you?
The pitch seems to get higher as it approaches, then drops as it moves away.

27. Motion of Galaxies
This is the Doppler effect: a change in the observed frequency of a wave that occurs when the source of the wave or the observer is moving.
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28. Motion of Galaxies
The Doppler effect occurs with light as well as sound.
Objects moving toward us have a “blue shift” because the light we are receiving is being compressed into shorter wavelengths.

29. Motion of Galaxies
Objects moving away from us have a “red shift” because the light we are receiving is seemingly stretched into longer wavelengths.

30. Motion of Galaxies
Most galaxies we observe from Earth have a red shift- meaning they are all moving away from us-and one another.

31. Motion of Galaxies
This supports the idea that the universe is expanding.

32. Development of the Universe
Because galaxies are moving apart, scientists concluded that there was a moment in time when the universe began to expand, which we call the big bang.
This occurred around billion years ago.

33. Development of the Universe
After the big bang, the universe was extremely dense and hot.
We still have a lot to learn about what the early universe was like.
Stars began forming after about 1 billion years.