Chapter 9: The Family of Stars

1. The distances to nearby stars are determined by the use of the parallax method. What is the parallax of a star and how is it measured. (Remember the relationship between distance and parallax is an inverse relationship.)

2. What is a parsec? How is it defined? What is the abbreviation (pc)? How many light years in a parsec?

3. What are the limits of the parallax method?

4. What is the proper motion of a star? How is it measured? Why do we need both distance and proper motion to determine the speed of a star across the line-of-sight?

5. What is meant by the apparent magnitude of a star? It was defined in chapter 2 on pages 13-15.

6. What is the absolute magnitude of a star?

7. The inverse square law of light is used in this section. It is defined only on page 82. It is important and I spent some time on it in class. Remember that it means that the brightness of a star decreases as the square of the distance.

8. Be familiar with table 9-1.

9. What is meant by the luminosity and surface temperature of a star?

10. What is the relationship between luminosity, radius, and temperature of a star? How is it obtained?

11. Make sure that you understand the examples on page 177- We can use the equation on this page to determine the radius of a star.

12. THE HERTZPRUNG-RUSSELL (HR) Diagram: Why is it important? What do we learn from it? Why do we use it to study stellar clusters?

13. What is the Main Sequence? Where is the Sun located in this diagram? What do H and R stand for? What is actually being plotted?

14. Where do most of the stars fall in this diagram? What is the physical significance of the Main Sequence? (Region where stars are fusing H to He in their cores.)

15. Where do the red giants and white dwarfs fall in the diagram?

16. What is the Luminosity Classification of the Sun? Why do we need a Luminosity Classification?

17. How does the main sequence lifetime of a star vary with mass and luminosity? Which stars live the longest? The shortest?

18. Skip Spectroscopic parallax.

19. How do we get the masses of binary stars?

20. What are the different types of binaries?

21. What is a light curve?