HOMEWORK 4
- Due: Tuesday, March 27.
- Review: Monday, March 26 in ECJ 1.202
from 6 to 7pm.
o Answer all questions in Part A and one from Part B.
NOTE: The exercises on Classnotes 11 may be completed as a substitute for Part B, that is: complete the two diagrams and attempt the 3 'questions' in the left hand column of the first page.
As before, Part B questions call for at least a few complete sentences. Part A questions may be answered on these sheets but the Part B question should be answered on separate sheets.
Part A
| A1. | If a star in the process of formation begins to increase its temperature, what will happen to the peak wavelength of its emitted radiation? |
| a. It will move
toward longer wavelengths (e.g.., visible to IR.) b. It will remain constant, since the chemical state of the gas will not change. c. It will not change, since it is not dependent upon temperature. d. It will move toward shorter wavelengths (e.g., IR to visible.) |
| A2. | Ionization of an atom occurs when |
| a. the nucleus
undergoes fission, or splitting b. an electron is removed from the atom. c. an electron is lifted from the ground state to an excited level. d. an electron is allowed to return to the ground state. |
| A3. | In a laboratory, the Balmer beta line has a wavelength of 486.1 nm. The line appears in a star's spectrum at 486.3 nm. Is the star approaching or receding? |
| A4. | A perfecy blackbody has which kind of spectrum? |
| a. absorption b. continuous c. emission line d. none (it emits no light) |
| A5. | The following diagram depicts the velocity (speed and direction) of several stars. |
 |
|
| You observe these stars (all at the 'same' large distance) from a position off to the LEFT. Please order them by increasing radial velocity from maximum radial velocity of approach to maximum radial velocity of recession. |
| A6. | Use Figure 9-11 (p.178) and the discussion of spectral classification to estimate the spectral class and the luminosity class of |
|
| A7. | Vega is about 3 times brighter than Deneb. Using Figure 9-11, estimate Deneb's distance given that Vega is about 25 LY from Earth. Show all work. |
| A8. | Six stars have the following spectral types; order them by decreasing surface temperature: |
| O5V, M3III, A2V, G2V, K0II, G5V |
| A9. | A red giant's size is that of |
| a. the Sun b. the Earth c. the Earth's orbit d. the state of Kansas e. a typical city |
| A10. | Main sequence stars have masses between |
a. 0.001 and 1000M b. 1 and 2 M c. 0.08 and 120 M d. 1/1000 and 106 M |
| A11. | The mass luminosity
relation L M4 applies to: |
| a. All stars b. White dwarfs c. Main sequence stars d. Red giants |
| A12. | The parallax of a star is 0.25 seconds of arc. How far away is it? |
| a. 25 light years b. 25 parsecs c. 4 light years d. 4 parsecs e. 0.4 parsecs |
| A13. | Stars UT-X and UT-Y have parallaxes of 0."1 and 0."02 respectively. If the stars are equally luminous, how much brighter will UT-X appear than UT-Y? Show all work. |
| A14. | The star cluster
UT301 contains 5 main sequence stars of spectral types G, O,
M, A, and F. Assume all stars are at the same distance. |
| Which star is hottest? Which star is reddest? Which star is brightest? Which star is the most massive? Which star is the most like our Sun? |
| A15. | What is the present age of the Sun? |
| a. 6.5 trillion years b. 4.5 trillion years c. 10 billion years d. 4.5 billion years |
| A16. | What are the five most common elements in the Sun's atmosphere? |
| A17. | What is meant by the term 'proper motion'? Your own words, please! |
| A18. | What is the mass ratio of the stars in Figure 10-5? Show all work. |
| A19. | What is the luminosity of a 4-solar mass main sequence star? |
| Describe how you obtained your answer. |
| A20. | If the interior temperature of a star increases, the immediate response of the star will be to |
| a. do nothing -- that is,
remain the same b. contract c. expand d. cease to exist but cool off to become a planet. |
Part B
| B1. | Complete the exercises set out on Classnotes 11. |
| B2. | a. | Describe,
with the aid of well-labelled diagrams, the method of trigonometric
parallax. Explain what is measured and how the measurements are related to the distance of the star under observation. |
| b. | Define clearly the distance unit called a parsec. | |
| c. | How have telescopes in space helped astronomers measure trigonometric parallaxes? |
| B3. | a. | Describe and sketch the H-R diagram for the sample of stars near the Sun (say within 20 parsecs). Label the axes. Indicate the range of the quantities plotted. |
| b. | On the diagram, locate the following stars: A1V, M21, K1III, and G2V, and the Sun. | |
| c. | Give the approximate radii (in terms of the Sun's radius) of stars in the following classes: G2 V, G2III, G2Ia. | |
| d. | How can the H-R diagram be used to find the distance to a main sequence star? State clearly the observations you would make and the assumptions you would adopt. |
| B4. | a. | In your own words, define these terms: spectroscopic binary, visual binary, and eclipsing binary. |
| b. | From Figure 10-12, estimate the period of this spectroscopic binary. | |
| c. | Why are the periods of all visual binaries measured in years, but the periods of many spectroscopic binaries are only a few days? |
| B5. | a. | After you strike a match, the hot gases in the flame soon disperse. The Sun and stars also consist of hot gases why do they not disperse also? |
| b. | Explain clearly why nuclear fusion occurs only in very hot gases. |
| B6. | a. | Describe the several steps in the argument that leads to the conclusion that the Sun must have a hot core (T~15 million K), and that it must currently be generating energy in the core. (It is not necessary to give me a description of the nuclear processes.) |
| b. | How long does it take electromagentic radiation emitted at the Sun's center to reach the surface? How long does it take radiation to travel the same distance in free space? Explain clearly why these two times differ by a very large factor. (The velocity of light is 300,000 km/sec. The radius of the Sun is 400,000 kms.) |
If silicon had been a gas, I should have been a Major General. [Explaining his failure at the chemistry paper in the West Point entrance examination.]
James Abbot McNeil Whistler
(1834-1903)
Youth is imaginative, and if the imagination can be strengthened by discipline, this energy of imagination can in great measure be preserved through life. The tragedy of the world is that those who are imaginative have but slight experience, and those who are experienced have feeble imagination. Fools act on imagination without knowledge, pedants act on knowledge without imagination. The task of a university is to weld together imagination and experience.
Alfred North Whitehead
(1861 - 1947)