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This exam contains seven questions, which has multiple parts. PLEASE be sure to attempt each question as some questions are easier than others. You can spend an average of 10 minutes on each question and finish the exam on time. The exams will be collected at 12:15 pm.

Each of the questions is worth a total of 10 points. The point value of each of sub-part of a question are listed. You should use complete and clear sentences in your explanation and discussions. Show all of your work in numerical problems and include the UNITS in your answer.

1. Descriptions...

a. (5 pts) What are the two underlying assumptions of special relativity?

b. (5 pts) Explain how absorption and emission lines arise. Be sure to cover what conditions are necessary to get absorption lines.

2. Astronomical coordinate systems.

a. (4pts) Explain the Right Ascension and Declination coordinate system. How it is defined.

b. (3pts) Explain what the ecliptic is.

c. (3pts) What does it mean to say that a source is transiting? Is the time that a source transits the same for someone in College Park as it is for someone in downtown DC?

3. Moons and more Moons...

a. (4pts) Explain why eclipses of the Sun occur and why they occur infrequently.

b. (3pts) How would eclipses change if the Earth was tilted on its axis by 50 degrees rather than 23.5 degrees? Assume that everything else in the solar system remained unchanged.

c. (3pts) If our Moon was rotating with a period of 48 hours, how long would it be between Earth rises as viewed from somewhere on the equator of the Moon. You should assume that the Moon is rotating in the same direction as it is orbiting the Earth. Remember that the orbital period of the Moon is 27.3 days.

4. Time, time, you gotta have time....

a. (4pts) Explain the differences between Coordinated Universal Time and Local Sidereal Time.

b. (3pts) If the local sidereal time right now is 20 hours and 40 minutes, how long will it be before an object at Right Ascension 2 hours 20 minutes crosses your meridian.

c. (3pts) What will be the LST for College Park this Friday night at 10 pm?

5. You are in your spaceship traveling toward the planet Neptune in our solar system.

a. (4pts) During the first part of your trip you are headed directly away from Earth at a velocity of 100 km/second. You are bored and want to listen to your favorite radio station which transmitts at a frequency of 101 Megahertz on your car radio dial on Earth. What frequency should you tune to with the radio in your spaceship?

b. (3pts) You have now arrived at Neptune and you are in orbit around the planet. You want to measure the mass of Neptune so you carefully measure your velocity to be 20 km/sec and you find that it takes you 8 hours to complete an orbit. What is the mass of Neptune?

c. (3pts) Your final job on Neptune is to fire a probe into the atmosphere. The idea is to shoot the probe off so that it falls gently into the atmosphere and its parahute can open to slow its descent. In what direct and at what speed would you fire the probe? Why?

6. You are given the job of trying to detect an Earth-like planet around a nearby star. You assume that the planet is orbiting the star at a distance of 1 AU and the star is located at a distance of 5 light-years from the Sun.

a. (4pts) How big of an optical telescope would be required to make an image which could resolve the planet from the star? Assume that you are going to take your images at a wavelength of 6000 Angstroms.

b. (3pts) Explain why such a telescope should be located in space.

c. (3pts) Calculate the total luminosity of the planet assuming that it is emitting like a blackbody with a temperature of 280 K. How does that compare to the luminosity of our Sun?

7. You have landed on the surface of planet Z.

a. (4pts) The planet is in an elliptical orbit around its sun with a closest approach to its sun of 0.5 AU and a farthest distance of 5 AU. What do you think the seasons will be like? You can assume that the rotation axis of the planet is tilted at 10 degrees with respect to the orbit.

b. (3pts) If the star has the same mass as our Sun, what will be the orbital period of the planet?

c. (3pts) You pull out your handy scale and weigh yourself. You weigh 53 pounds. Assuming that the radius of the planet is 1/2 that of Earth, what is the mass of the planet?