Chapter Twenty-Seven: Stars

1. Chapter Twenty-Seven: Stars • 27.1 The Sun • 27.2 Stars • 27.3 The Life Cycle of Stars

2. NGC 3532 in the constellation Carina ESO/G.Beccari

3. 27.2 How are stars classified? • Astronomers classify stars according to:

4. 27.2 How are stars classified? • Astronomers classify stars according to: • size/mass,

5. 27.2 How are stars classified? • Astronomers classify stars according to: • size/mass, • temperature,

6. 27.2 How are stars classified? • Astronomers classify stars according to: • size/mass, • temperature, • color, and

7. 27.2 How are stars classified? • Astronomers classify stars according to: • size/mass, • temperature, • color, and • brightness.

8. 27.2 What is the size of stars? • Stars come in a range of sizes and masses.

9. 27.2 What is the size of stars? • Stars come in a range of sizes and masses. • Our Sun is a medium-sized star.

10. 27.2 What is the size of stars? • Stars come in a range of sizes and masses. • Our Sun is a medium-sized star. • The largest stars, giant stars have a mass of about 60 times the mass of the Sun.

11. The sun is considered a __________ star. • Giant • Medium-sized • Dwarf

12. 27.2 The size of stars • There are two types of giant stars.

13. 27.2 The size of stars • What are two types of giant stars? • Red giants are cooler than white stars.

14. 27.2 The size of stars • What are two types of giant stars? • Red giants are cooler than white stars. • Blue giant stars are hot and much more massive than our sun.

15. Which star is cooler, a blue giant or a red giant?

16. 27.2 The size of stars • Stars that are smaller than the sun come in two main categories, dwarfsand neutron stars.

17. 27.2 The size of stars • Stars that are smaller than the sun come in two main categories, dwarfsand neutron stars. • Sirius, the Dog Star, is the largest known white dwarf.

18. 27.2 How is temperature and color related with stars? • If you look closely at the stars on a clear night, you might see a slight reddish or bluish tint to some stars.

19. 27.2 How is temperature and color related with stars? • If you look closely at the stars on a clear night, you might see a slight reddish or bluish tint to some stars. • This is because their surface temperatures are different.

20. 27.2 Temperature and color • The color of light is related to its energy.

21. 27.2 Temperature and color • The color of light is related to its energy. • White light is a mixture of all colors at equal brightness.

23. 27.2 Brightness and luminosity • Brightness, also called intensity, describes the amount of light energy per second falling on a surface.

24. 27.2 Brightness and luminosity • For a distant source of light like a star, the brightness decreases as the inverse square of the distance.

25. What does the inverse square law mean?

27. 27.2 Brightness and luminosity • Luminosity is the total amount of light given off by a star in all directions. .

28. 27.2 Brightness and luminosity • Luminosity is the total amount of light given off by a star in all directions. • Luminosity is a fundamental property of a star whereas brightness depends on both luminosity and distance.

29. 27.2 Temperature and luminosity • In the early 1900s, Danish astronomer Ejnar Hertzsprung and American astronomer Henry Russell developed an important tool for studying stars.

30. 27.2 Temperature and luminosity • In the early 1900s, Danish astronomer Ejnar Hertzsprung and American astronomer Henry Russell developed an important tool for studying stars. • Their graph showed luminosity on the y axis…

31. 27.2 Temperature and luminosity • In the early 1900s, Danish astronomer Ejnar Hertzsprung and American astronomer Henry Russell developed an important tool for studying stars. • Their graph showed luminosity on the y axis… • …and surface temperature on the x axis

33. 27.2 Temperature and luminosity • H-R diagrams are useful because they help astronomers categorize stars into groups: ?

34. 27.2 Temperature and luminosity • H-R diagrams are useful because they help astronomers categorize stars into groups: • Main sequence stars, like the Sun, are in a very stable part of their life cycle.

35. 27.2 Temperature and luminosity • H-R diagrams are useful because they help astronomers categorize stars into groups: • Main sequence stars, like the Sun, are in a very stable part of their life cycle. • White dwarfs are hot and dim and cannot be seen without a telescope.

36. 27.2 Temperature and luminosity • H-R diagrams are useful because they help astronomers categorize stars into groups: • Main sequence stars, like the Sun, are in a very stable part of their life cycle. • White dwarfs are hot and dim and cannot be seen without a telescope. • Red giants are cool and bright and some can be seen without a telescope.

37. 27.2 Temperature and luminosity • H-R diagrams are useful because they help astronomers categorize stars into groups: • Main sequence stars, like the Sun, are in a very stable part of their life cycle. • White dwarfs are hot and dim and cannot be seen without a telescope. • Red giants are cool and bright and some can be seen without a telescope. Can you locate blue giants on the H-R diagram?

41. Chapter Twenty-Seven: Stars • 27.1 The Sun • 27.2 Stars • 27.3 The Life Cycle of Stars

42. 27.3 The life cycle of stars • A star, regardless of its size, begins its life inside a huge cloud of gas (mostly hydrogen) and dust called a nebula.

43. 27.3 The life cycle of stars • A star, regardless of its size, begins its life inside a huge cloud of gas (mostly hydrogen) and dust called a nebula. • The Eagle Nebula is the birthplace of many stars.

44. 27.3 The life cycle of stars • A protostaris the earliest stage in the life cycle of a star.

45. 27.3 The life cycle of stars • A protostaris the earliest stage in the life cycle of a star. • The Orion Nebula was the birthplace of these protostars.

46. 27.3 The life cycle of stars • A star is born when temperature and pressure at its center become great enough to start nuclear fusion.

47. 27.3 The life cycle of stars • A star is born when temperature and pressure at its center become great enough to start nuclear fusion. • Once nuclear fusion begins, a star is in the main sequence stage of its life cycle.

48. 27.3 The life cycle of stars • The time a star stays on the main sequence depends on the star’s mass.

49. 27.3 The life cycle of stars • The time a star stays on the main sequence depends on the star’s mass. • High-mass stars burn brighter, and hotter, using up their hydrogen faster than low-mass stars.

50. 27.2 The old age of Sun-like stars • With no more energy flowing outward, nothing prevents gravity from crushing the matter in the core together.