1. 1- Where is our sun in the H-R diagram. 2- What color is our sun
1- Where is our sun in the H-R diagram? 2- What color is our sun? 3- How much longer will our sun last? 4- What is the next stage of our sun?

2. Chapter 26 Stars and Galaxies Section 3 Galaxies

3. Chapter 26 Section 3
Before you read - write the reading’s objectives in this space:
1 – _______________________________________
______________________________________________________________________________________________________________________________
2 – _______________________________________
3 - ________________________________________

4. Chapter 26 Section 3
Before you read - write the reading’s objectives in this space:
1 – Explain the same natural laws that apply in the Milky Way galaxy also apply in other galaxies
2 – Compare the three main types of galaxies.
3 – Describe the Milky Way galaxy and the Sun’s position in it.

5. What is a galaxy? _____________________________
__________________________________________
What is our galaxy called? _______________________
It contains 400 billion stars, by most recent estimates, including the Sun. 1

6. What is our galaxy called? The Milky Way
What is a galaxy? A large group of stars, gas, and dust held together by gravity.
What is our galaxy called? The Milky Way
It contains 400 billion stars, by most recent estimates, including the Sun. 1

7. Describe spiral galaxies. _________________________
____________________________________________________________________________________ 2

8. Describe spiral galaxies
Describe spiral galaxies. Spiral galaxies have spiral arms that wind outward from the galaxy’s center. These spiral arms are made up of bright stars, dust, and gas. 2

9. Describe barred spiral galaxies. ____________________
____________________________________________________________________________________ 3

10. Describe barred spiral galaxies
Describe barred spiral galaxies. Barred spirals have spiral arms extending from a large central bar of stars, dust, and gas that passes through the center, or hub, of the galaxy. 3

11. Describe elliptical galaxies. ________________________
________________________________________________________________________________________ 4

12. Describe elliptical galaxies
Describe elliptical galaxies. Elliptical galaxies are shaped like large, three-dimensional ellipses. Many are football-shaped, but other are spherical. 4

13. Describe irregular galaxies. ________________________
____________________________________________________________________________________________________________________________________ 5

14. Describe irregular galaxies
Describe irregular galaxies. Most galaxies that aren’t elliptical or spiral are considered irregular galaxies. They take many different shapes and contain 100 million to 10 billion stars, making them larger than dwarf ellipticals but smaller than spirals. 5

15. Just as stars are grouped together within galaxies, galaxies are grouped into clusters. What cluster does our Milky Way galaxy belong to? __________________________________________________About how many galaxies are in our group? ________________ ___________________________________________________________________________________________________What is the largest galaxy in our group?_____________________
Andromeda Galaxy – our next nearest “galactic neighbor.” Since the light from this galaxy left 2.5 million years ago, it’s like looking into the past 2.5 million years. 6

16. What is the largest galaxy in our group? Andromeda
Just as stars are grouped together within galaxies, galaxies are grouped into clusters. What cluster does our Milky Way galaxy belong to? The Local Group.
About how many galaxies are in our group? It is a relatively small cluster containing about 45 galaxies of various types and sizes but most are dwarf elliptical galaxies.
What is the largest galaxy in our group? Andromeda
Andromeda Galaxy – our next nearest “galactic neighbor.” Since the light from this galaxy left 2.5 million years ago, it’s like looking into the past 2.5 million years. 6

17. According to current astronomers, how do galaxies form?
____________________________________________________________________________________________________________________________________________________________________________________ 7

18. According to current astronomers, how do galaxies form?
Galaxies grow by absorbing or merging with other smaller objects. Galaxy collisions have a strong effect on the overall structure and shape of the colliding galaxies. 7

19. What happens to individual stars within colliding galaxies?
________________________________________________________________________________________________________________________________________________ 8

20. What happens to individual stars within colliding galaxies?
There is so much space between it appears that little happens. 8

21. The Milky Way’s disk is about ________________ thick.
What kind of galaxy is the Milky Way galaxy believed to be? _______________________________________
The Milky Way galaxy measures about _____________ from one side to the other.
The Sun lies about _________________from the galactic center on the edge of one of the spiral arms.
The Milky Way’s disk is about ________________ thick. 9

22. The Milky Way’s disk is about 1,000 light-years thick.
What kind of galaxy is the Milky Way galaxy believed to be? A spiral but might be a barred spiral galaxy.
The Milky Way galaxy measures about 100,000 light-years from one side to the other.
The Sun lies about 26,000 light-years from the galactic center on the edge of one of the spiral arms.
The Milky Way’s disk is about 1,000 light-years thick. 9

24. What are contained in the spiral arms of galaxies? __________________
______________________________________________________
What do recent theories suggest may exist in the center of galaxies? ____
__________________________ 10

25. What are contained in the spiral arms of galaxies
What are contained in the spiral arms of galaxies? The arms contain both young stars and prestellar material, such as glowing nebulae.
What do recent theories suggest may exist in the center of galaxies? Extremely massive black holes might exist at the cores of galaxies. 10

26. Question 1 3 Which is NOT a type of galaxy? A. elliptical B. irregular
Section Check 3
Question 1
Which is NOT a type of galaxy?
A. elliptical
B. irregular
C. round
D. spiral 11

27. Section Check 3
Answer
The answer is C. “Round” is not recognized as a major type of galaxy. 11

28. Question 2 3 How do galaxies grow? A. by producing new stars
Section Check 3
Question 2
How do galaxies grow?
A. by producing new stars
B. by emitting light
C. by absorbing other galaxies
D. by absorbing stars that don’t belong to other
galaxies 12

29. Section Check 3
Answer
The answer is C. The Milky Way has been gobbling up the Sagittarius dwarf elliptical galaxy for 2 billion years. 12

30. Question 3 3 Where is the Sun located in the Milky Way galaxy?
Section Check 3
Question 3
Where is the Sun located in the Milky Way galaxy?
A. at the center of the galaxy
B. at the edge of one of the spiral arms
C. 100,000 light-years from the center
D. 1,000 light-years from the center 13

31. Section Check 3
Answer
The answer is B. The Sun lies about 26,000 light-years from the center of the galaxy on the edge of one of the spiral arms. 13