Galaxies and the Universe 25-4 Notes

1. We are in the solar system. The solar system is in a galaxy called the
Milky Way.

2. A galaxy is a large group of stars, gas, and dust held together by gravity.
galaxies are grouped into clusters. The Milky Way is part of a cluster called the Local Group

3. There are three major types of galaxies
Spiral galaxies have spiral arms that wind outward from the center. The arms are made up of bright stars, dust, and gas.
 
4. The Milky Way galaxy is a spiral galaxy.

5. Elliptical galaxies are a common type of galaxy. They are shaped like large, three-dimensional ellipses.

6. Irregular galaxies include all the galaxies that don’t fit into the other two groups. These galaxies have many different shapes.

7. The Milky Way is about 100,000 light-years across

8.  A Light year is the distance light travels in a year (9.5 trillion kilometers)

9. Our Solar system is about 26,000 light-years from the galaxy’s center in one of the spiral arms.

10. It takes about 225 million years for the Sun to orbit the center of the Milky Way.

11. You can’t see the shape of the Milky Way because the location of our solar system is in one of its spiral arms.

12. You can see the Milky Way stretching across the sky. It looks like a dusty band of dim light.

13. Like many other galaxies, the Milky Way has a black hole at its center.

14. Scientists have offered different models, or ideas, for how the universe began. One model is the steady state theory. It suggests that the universe always has been the same as it is now.

15. A second model is the oscillating model. This model states that the universe formed and then it expanded, or grew larger. Over time, the rate of growth slowed down. Then the universe began to contract, or shrink.

16. A third model is called the big bang theory. This theory states that the universe began with a big bang and has been expanding ever since.

17. When a star is moving away from Earth, the light shifts toward red. This is called a red shift.

18. In 1929, Edwin Hubble noticed a red shift in the light from galaxies outside the Local Group. This meant the galaxies are moving away therefore the entire universe must be expanding.

19. The universe is all of space and all the matter and energy in it.

20. The Big Bang Theory states that the universe was created sometime between 10 billion and 20 billion years ago when a cosmic singularity exploded and hurled matter and in all directions.

21. Galaxies are large systems of stars and interstellar matter held together by gravity and contain millions of stars.

22.Irregular galaxies have no real shape, contain very hot newer stars and have lots of dust and gases for new stars.

23. Spiral galaxies are shaped like pinwheels and have a central bulge with many older red stars and the spirals or arms contain material for new stars. 

24. Elliptical galaxies are ball or oval shaped, contain mostly older stars, and very little material for new stars.

25.The Milky Way Galaxy is our galaxy and it is a spiral galaxy.