Astronomy 106 Review for Test #4

Fall 2006

The Properties of Stars

1. What are two properties we know about all stars?

2. What is the most fundamental way of determining the distance to a star?

3. How is the surface temperature of a star determined?

4. What are two ways of determining the diameters of the stars

5. How is the mass of a star determined?

6. How do we find the chemical composition of the stars?

The New Astronomy

1. State the three laws of spectroscopy established by Wilhelm Bunsen and Gustav Kirchhoff.

2. For what did Father Angelo Secchi devise a classification scheme?

3. List the seven major stellar spectral classes in the sequence we use today.

4. Know the relationship between the spectral classes and temperature

5. Know the relationship between the spectral classes and color.

6. Draw a rough sketch of the HR diagram and label the axes, the regions of the Main Sequence, Red Giants, and White Dwarfs

7. In what era did Annie Jump Cannon live and for what is she remembered today?

8. Explain the phenomenon known as the Doppler effect.

9. What do we mean when we say that a star is blue shifted or red shifted?

10. What was the definition of the word nebula as used by astronomers in the 19^th century?

11. Who invented the diffraction grating and what is it used for?

12. Be able to do the "which star is closer?" exercise like we did in class using the HR diagram.

The Great Debate

1. What were the two major schools of thought about the nature of the nebulae in the 19^th century?

2. What is the “zone of avoidance” and what did most astronomers at the end of the 19^th century believe this indicated about the nature of spiral nebulae?

3. Who was Lord Rosse, and what significant discovery did he make?

4. Why was the nova that appeared in M31 (the Andromeda nebula) believed to discredit the “Island Universe” theory?

5. Who was Henrietta Leavitt, in what era did she live, and for what is she remembered today? Explain how she arrived at her discovery and why it is important in determining the structure of the universe.

6. Give three arguments against the idea that some nebulae are external galaxies (“island universes”)

7. Give three arguments in favor of the idea that some nebulae are external galaxies (“island universes”)

8. How did Harlow Shapley come to the conclusion that the sun is not in the center of the Milky Way?

Edwin Hubble

1. What key piece of evidence did Edwin Hubble find which effectively settled the “Great Debate”?

2. How did van Maanen’s rotation data for spiral nebula cast doubt on the idea that spiral nebulae were distant galaxies? How was the problem solved in favor of those who supported the external galaxy theory?

3. What three main things is Edwin Hubble remembered for?

4. Sketch and label Hubble’s “tuning fork” diagram for galaxies.

5. What did Hubble discover from studying the spectra of external galaxies?

6. The diagram below is a Hubble diagram which shows the relationship between the distances and recession velocities of galaxies. Label the x-axis and the y-axis and give the units. How did Hubble determine the y-axis value for each point? The x-axis value? How would you find the Hubble constant from this diagram?

What is the universe made of?

1. Why are the hydrogen absorption lines in coolest stars (M) so weak?

2. Why are the hydrogen absorption lines in the very hottest stars (O) so weak?

3. Why are the hydrogen absorption lines in moderately hot stars (A) so strong?

4. What is the most abundant element in all stars?

5. Whose model of the universe did Cecilia Payne use to do her work?

6. Who originally proposed the atomic theory in ancient times?

7. Who is credited with reviving the atomic theory in the 18^th century?

8. The above diagrams show the Bohr hydrogen atom in different energy states. Be sure you know which is the ground state, excited state, and ionized state.

9. Know what these words mean: atom, electron, proton, neutron, ion

10. What part of the atom defines the element (what makes carbon carbon)?

11. Sketch and label the Bohr atom for hydrogen in the ground state

12. Sketch and label the Bohr atom for hydrogen in an excited state.

13. What is dark matter?

14. What type of radiation is emitted by hydrogen atoms in interstellar space?

15. What did Vera Ruben discover about the rotation of galaxies?

16. Who was the first woman to become full professor at Harvard?

17. Visible light is emitted from a hydrogen atom when an electron falls to the second orbit. What type of radiation is emitted when an electron falls to the first orbit (a longer drop) and what type is emitted when an electron falls to the third orbit (a shorter drop)?

18. How can astronomers tell how fast a galaxy is rotating?