# Astronomy Final

Topics: Star, Universe, Solar System Pages: 8 (1913 words) Published: August 24, 2013
Multiple Choice (Answer all 40 Questions)
Type in the letter that represents your best answer to the corresponding question from the original final exam document.

1. B
2. E
3. D
4. D
5. B

6. A
7. D
8. B
9. C
10. B

11. A
12. C
13. A
14. C
15. A

16. C
17. C
18. C
19. D
20. D

21. B
22. D
23. A
24. C
25. D

26. C
27. A
28. E
29. E
30. C

31. A
32. D
33. A
34. A
35. C

36. A
37. E
38. D
39. C
40. D

Problems (Answer all six Questions)
Complete these answers in your own words. Follow instructions in the Final Examination document. Answer all questions according to the instructions. Number each question here according to its number in the Final Examination document provided by your instructor.

1.(a) Kepler’s 3rd law
P^2 = a^3 (P = period in years; a = distance in AU)
75^2 = a^3
a = (75^2)^(1/3) = 17.78 AU.

(b) The further comets are from the sun, the slower they travel; therefore, it spends longer at the further distance.

2. (a) Star B is farther away. Its parallax is less. The closer a star is, the more its position changes against the background as the earth revolves around the sun. That is what parallax is.

(b) 20 parsecs. (One parsec = distance at which a star has a parallax of 1 arcsecond) Since this parallax is 1/20 as large, its distance is 20 times greater.

(c) 65.2 light years. (1 parsec = 3.26 ly * 20)

3. (a) 10m would have the greater light gathering power

(b) Both of the telescopes are in vacuum. The 10m one has area Pi r ^2, with r = 5m and the 2m one has r = 1. The ratio of Pi 5^2/Pi 1^2 = 25. Twenty-five times more light falls onto the large telescope.

(c) The 10m telescope has a “Greater” light gathering power.

(d) The factor would be about 25 times the light gathering power.

(e) Normally, light gathering power ratios are just the ratios of the areas. Due to the atmosphere on earth, there could be some absorption, however, since the wavelength is not specified, it wouldn’t hold true. Since the atmosphere acts like a gradient index lens, the amount of light that hits the earth telescope would have a very small increase thus refracting light towards the telescope. If there were no atmosphere, it would have continued at a larger angle and missed the telescope.

4. (a) d = 10,000 =100Mpc
100

(b) d = V d = 10,000 = 200Mpc
H0 50

(c) If universe is flat and composed mostly of matter, then the age of the Universe is 2 3H0
In the case of a very low density of matter the extrapolated age is larger. Age of universe = 1
H0
So the Universe is directly proportional to H0

5. Gx = GMm/r^2
G_new = GMm / (3r)^2 = GMm / 9r^2
(a) The force is 1/9 times (b) 9 times weaker

6. 15000/3000)^4
(a) The blue star is 625 times (b) more luminous

Essay (Answer all nine Questions)
Complete these answers in your own words. Follow instructions in the Final Examination document. Answer all questions according to the instructions. Number each question here according to its number in the Final Examination document provided by your instructor. 1.

a.H-R Diagram A (Very Young Cluster)
b.H-R Diagram D (Young Cluster)
c.H-R Diagram B (Old Cluster)
d.H-R Diagram C (Very Old Cluster)
Similar to the sun, stars will spend a majority of their life on the main sequence. We can view this by looking at the H-R diagram, which shows a ‘dense concentration’ of stars along a constricted belt from the upper left to the lower right. The mass of the star determines where on the main sequence it is located and how soon the star will move away from the main sequence. The age of the cluster can be estimated by viewing a cluster of stars on the HR diagram in reference to where they end on the main sequence....

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