Phys_306_Final

Basic Astronomy (Physics 306) Final Exam

Please give clear, specific, and unambiguous answers. See the last page for useful information.

Partial credit will not ordinarily be given on the short-answer questions (unless indicated otherwise). Partial credit WILL be given on problems marked with an asterisk *.

Each short answer is worth 3 points, unless indicated otherwise. Fill in the blank, circle the correct answer, etc., as indicated. In the fill-in-the-blank questions, any truly correct (and unambiguous) answer will receive full credit.

1. Which planet was discovered by William Herschel in 1781?

___________________________________________

2. He also discovered Titania in 1787. What is this object?

___________________________________________

3. What is the origin of the energy which produces the volcanic activity on earth?

___________________________________________

4. What is the origin of the energy which produces the volcanic activity on Io?

____________________________________

5. Which planet rotates backwards, in the sense that its rotation on its axis is opposite in direction to its rotation around the sun?

____________________________________

6. The polar caps on Mars are composed of frozen

____________________________________.

7. Name four gases that are abundant in the atmospheres of the outer planets -- for example, in the atmosphere of Neptune.

________________________________________________________________________

8. The atmosphere of Venus is composed primarily of

____________________________________

and what little water there is occurs mainly in the form of

____________________________________.

9. In human history (specifically the year 1610), what do Io, Europa, Callisto, and Ganymede have in common?

_________________________________________________________________________________

10. Explain briefly but clearly how extrasolar planets are detected.

_________________________________________________________________________________

11. What is the Oort cloud? Again, your answer should be brief but clear, and reasonably complete.

_________________________________________________________________________________

12. Pluto and its moon Charon revolve around their common center of gravity. What is the interesting feature of their relative orientation as they perform this orbital motion?

_________________________________________________________________________________

13. Why is Mars red?

_________________________________________________________________________________

14. What is the relationship between the rotational period of Mercury (for the rotation of the planet on its axis) and the orbital period (for the revolution of the planet around the sun)?

_________________________________________________________________________________

14. * (8) Deimos orbits Mars at a distance of 23,500 km and has a period of 1.262 days. Calculate the mass of Mars in kg.

14. (4) The diameter of Jupiter is 142,900 km and the distance from Jupiter to Io is 422,000 km. What is the angular diameter of Jupiter as seen from Io, in degrees? [If you were standing on Io, it would be a very imposing sight to see Jupiter hanging overhead!]

____________________________________

15. (4) If we observe light reflected from Saturn's rings, we should see a red shift at one edge of the rings and a blue shift at the other edge. If we observe a spectral line and see a difference in wavelength of 0.056 nm, and the unshifted wavelength is 500 nm, what is the orbital velocity of particles at the outer edge of the rings?

____________________________________

16. (4) If an asteroid has a surface temperature of 150 K, at what wavelength will it radiate the most energy?

____________________________________

18. * (6) Give a reasonably detailed description of how the solar system and earth came into being. For example, describe why the inner and outer planets are so different, why the earth has its internal structure and the kind of atmosphere that it has, why the planets rotate in essentially the same plane, why the various planets have the compositions that they have, and what is the most probable origin of the earth's moon. Please be clear and specific.

19. The Tully-Fisher relation is the relation between the absolute brightness (or luminosity) of a galaxy and its

____________________________________.

20. In 1912, Henrietta Leavitt discovered the single most important tool for establishing the distances of stars in our own and nearby galaxies -- a type of star known as

____________________________________.

21. The resolution of standard earth-based telescopes is limited to about

(a) 0.0001 arcsecond

(b) 0.001 arcsecond

(d) 0.1 arcsecond

(e) 1 arcsecond

(f) 10 arcseconds.

22. (6) In the Hertzsprung-Russell diagram, the vertical axis represents

____________________________________

and the horizontal axis represents

____________________________________.

23. Match the color of a star with its temperature, by writing "red", "blue", or "yellow" after each of the following temperatures.

20, 000 K ______________________

6000 K ______________________

3000 K ______________________

24. In the movie "Frequency", solar flares are supposed to produce a channel in spacetime between 1969 and 1999. If the mechanism involved sunspots instead, the more natural years would have been 1968 and 2001. Why is this?

_________________________________________________________________________________

25. The northern lights (or aurora borealis) figure prominently in this movie. What causes this phenomenon?

_________________________________________________________________________________

26. What is the approximate temperature at the center of the sun?

____________________________________

27. What is the approximate temperature at the surface of the sun?

____________________________________

28. Describe the basic nuclear reaction which powers the sun.

_________________________________________________________________________________

29. About how long does it take for energy generated at the center of the sun to make its way to the surface?

(a) 1 second

(b) 1 minute

(d) 6.5 hours

(e) a year

(f) a million years

30. Why is it hotter during the summer than during the winter? [Recall that 21 of 24 graduating Harvard seniors answered this incorrectly when interviewed on videotape. We expect Aggies to do better!]

_________________________________________________________________________________

31. The axis of rotation of the earth precesses with a period of approximately

(a) 76 years

(b) 760 years

(d) 4000 years

(e) 26,000 years

(f) 2,600,000 years

32. The axis of rotation of the earth is inclined from the vertical (i.e., the direction perpendicular to the plane in which the earth revolves around the sun) by approximately

(a) 1.5 degrees

(b) 3.5 degrees

(d) 75.5 degrees

(e) 85.5 degrees

33. Which of the following are not electromagnetic waves? (Circle all correct answers.)

(a) light

(b) infrared radiation

(d) radio waves

(e) gamma rays

(f) x-rays

(g) microwaves

(h) none of the above -- i.e., all are electromagnetic waves

34. The Chandra x-ray observatory, launched shortly before the beginning of this course, cost 1.5 billion dollars. Why is it essential to have an x-ray observatory outside the earth's atmosphere?

_________________________________________________________________________________

35. The Ring Nebula in Lyrae is a planetary nebula with an angular diameter of 73 seconds of arc and a distance of 5000 light years. What is its linear diameter?

____________________________________

36.* A neutron star and a white dwarf orbit each other with a period of 20 minutes. Suppose that the neutron star has a mass of 1.5 and that the white dwarf has a mass of 1.0, measured in solar masses.

(a) (6) What is the separation of the neutron star and the white dwarf, in kilometers?

(b) (2) How far is the white dwarf from the center of mass, again in kilometers?

37. (4) What is the radial velocity of 3C48 if its redshift is 0.37?

____________________________________

38. (4) If two stars differ by 7.6 magnitudes, what is the difference in their intensities?

____________________________________

39. How does the light-gathering power of the Hale telescope on Mount Palomar (with a mirror 5 meters in diameter) compare with that of the human eye (with a pupil 0.8 cm in diameter)? Express your answer as a ratio greater than one.

____________________________________

40. If you find a galaxy that contains globular clusters which are 1 second of arc in diameter, approximately how far away is the galaxy? Assume that a globular cluster is about 25 parsecs in diameter.

____________________________________

41. Suppose that an object is at 300 K, and is emitting blackbody radiation. If the temperature is increased to 3000 K, by what factor will the energy radiated increase? (This is the energy per second and per square meter.)

(a) 10,000.000

(b) 1,000,000

(d) 10,000

(e) 1000

(f) 100

(g) 10

42. Which of the following elements primarily formed in the big bang, which was formed primarily by the burning of stars, and which was formed primarily by supernovae? Put the appropriate phrase in each blank.

carbon _______________________________________________

gold _______________________________________________

deuterium (or heavy hydrogen) ____________________________

____________________________________________________________________________________

Have a pleasant summer!