1. © 2010 Pearson Education, Inc. Most luminous stars: 10 6 L Sun Least luminous stars: 10 –4 L Sun (L Sun is luminosity of Sun)

2. © 2010 Pearson Education, Inc. How do we measure stellar temperatures?

3. © 2010 Pearson Education, Inc. Hottest stars: 50,000 K Coolest stars: 3000 K (Sun’s surface is 5800 K.)

4. © 2010 Pearson Education, Inc. Absorption lines in star’s spectrum tell us its ionization level.

5. © 2010 Pearson Education, Inc. Lines in a star’s spectrum correspond to a spectral type that reveals its temperature. (Hottest) O B A F G K M (Coolest)

6. © 2010 Pearson Education, Inc. (Hottest) O B A F G K M (Coolest) Remembering Spectral Types Oh Boy, A Funky Goat Kicked Me Only Baby Armadillos Feature Good Kodak Moments Olivia Brings Alyssa Five Gigantic Krispy Muffins Ostriches Battle Aardvarks For Grape Koolaid Material Our Bay Area Fans Giant Killing Machine Oreo Biscuits Are For Great Kids Mmmm…..

7. © 2010 Pearson Education, Inc. Clicker Question Which kind of star is hottest? A. M star B. F star C. A star D. K star

8. © 2010 Pearson Education, Inc. Clicker Question Which kind of star is hottest? A. M star B. F star C. A star D. K star

9. © 2010 Pearson Education, Inc. Pioneers of Stellar Classification Annie Jump Cannon and the “calculators” at Harvard laid the foundation of modern stellar classification.

10. © 2010 Pearson Education, Inc. Most massive stars: 100M Sun Least massive stars: 0.08M Sun (M Sun is the mass of the Sun.)

11. © 2010 Pearson Education, Inc. Largest star known is VY Canis Majoris. It is a red hypergiant, ~ 2,000 solar radii or ~ 1.9 billion miles in diameter. If it were in our solar system, its size would extend past Uranus. It is ~ 4,900 light years away.

12. © 2010 Pearson Education, Inc. What is a Hertzsprung-Russell diagram?

13. © 2010 Pearson Education, Inc. Temperature Luminosity An H-R diagram plots the luminosity and temperature of stars.

14. © 2010 Pearson Education, Inc. Most stars fall somewhere on the main sequence of the H-R diagram.

15. © 2010 Pearson Education, Inc. Stars with lower T and higher L than main- sequence stars are larger and are called giants and supergiants.

16. © 2010 Pearson Education, Inc. Stars with higher T and lower L than main- sequence stars are smaller and are called white dwarfs.

17. © 2010 Pearson Education, Inc. A stars full classification includes spectral type and luminosity class. Every spectral type is subdivided into 10 subtypes. For example: A0, A1, A2 ….A9, F0, F1, …..F9, etc. I - supergiant II - bright giant III - giant IV - subgiant V - main sequence Examples: Sun - G2 V Sirius - A1 V Proxima Centauri - M5.5 V Betelgeuse - M2 I

18. © 2010 Pearson Education, Inc. Temperature Luminosity H-R diagram depicts: Temperature Color Spectral type Luminosity Radius

19. © 2010 Pearson Education, Inc. Which star is the hottest? Temperature Luminosity

20. © 2010 Pearson Education, Inc. Which star is the hottest? A Temperature Luminosity

21. © 2010 Pearson Education, Inc. Which star is the most luminous? Temperature Luminosity

22. © 2010 Pearson Education, Inc. Which star is the most luminous? C Temperature Lumiosity

23. © 2010 Pearson Education, Inc. Which star is a main- sequence star? Temperature Luminosity

24. © 2010 Pearson Education, Inc. Which star is a main- sequence star? D Temperature Luminosity

25. © 2010 Pearson Education, Inc. Which star has the largest radius? Temperature Luminosity

26. © 2010 Pearson Education, Inc. Which star has the largest radius? C Temperature Luminosity