Homework 6, Astr 305V, due: November 29, 2018

This homework is rather different in nature than the others. It is a set of example exam questions that will encourage you to study some of the recent material we discussed, and also help prepare you for the exam. The difference is, you can use your book and notes for this homework. So, you should be able to do well on these questions. Please turn in no later than May 3.

WRITE THE ANSWERS CLEARLY ON A SEPARATE SHEET. DO NOT REWRITE THE QUESTION, JUST LIST THE QUESTION NUMBER AND YOUR ANSWER.

1. True or false? Even though no object with mass, and no information, can travel faster than the speed of light, in principle an astronaut could reach a star that is 500 light years away within the current average human life span.

2. According to the theory of special relativity, two electrons moving at close to the speed of light in opposite directions, that collide head-on, meet with a relative speed of:

a. almost twice the speed of light.

b. exactly the speed of light.

c. almost the speed of light.

d. much less than the speed of light but still super fast man!

3. In the SETI project, we search for evidence that intelligent civilizations exist elsewhere. Which of the following comes closest to most of the activities that researchers in the SETI project do?

a. They send signals, sit back, relax, and wait for a message back.

b. They search for non-naturally occurring radio waves towards other stars.

c. They investigate UFO sightings on Earth.

d. They raise money to go back to the Moon.

4. The "water hole" in SETI would fall in which wavelength or color range?

a. Visible light

b. Between about 1 and 2 m wavelength.

c. Between 18 and 21 cm wavelength.

a. In the Infrared wavelength regime.

5. In the Doppler method for detecting extra-solar planets, we measure:

a. The motion of the planet by measuring the changes in velocity of the planet over time.

b. The motion of the star by measuring the changes in velocity of the star over time.

c. The change in brightness of the star over time.

d. The light coming from the planet, by blocking out the star's light.

6. Suppose that you are on a nearby star and look at the Solar System. You happen to see the Sun's brightness dimming as Jupiter transits across its disk. Given that Jupiter's diameter is about 10 times smaller than the Sun's diameter, how much fainter will the Sun become during this transit, compared to its normal brightness?

a. A factor 0.1 (so 10%). c. Only about one in a million.

b. A factor 0.01 (so 1%). d. There would be no effect on the Sun's brightness.

7. When a planet orbits a star, the star will also move in its own orbit. The star's orbit

a. is the same size as the planet's orbit.

b. is smaller than the planet's orbit by the ratio of the masses of planet and star.

c. is smaller in size than the planet's orbit and has a longer orbital period.

d. is generally more elliptical than the planet's orbit.

8. Einstein developed the theories of special relativity in the early part of the 20th century. List two consequences, or "properties" if you like, of the theory of special relativity that are quite different from the prediction of how things behave under Newton's laws of motion.

9. How is the "habitable zone" defined for a star-planet system? In other words, what do we require for a planet in order that it might be in the habitable zone?

10a. Describe which quantity the Drake equation is trying to estimate.

10b. List at least 2 relevant parameters or quantities that enter into the Drake equation.

11. Explain why the Fermi paradox is a "paradox". So, what is meant with a paradox and show that this example meets that description.