Download ASTR 342: Summer 2008 Homework Set #1 and more Assignments Astronomy in PDF only on Docsity! ASTR 342: Summer 2008 Homework set #1 INSTRUCTIONS: Answer each part of the following questions. For mathematical questions, be sure to show your work and circle your final answer. Do not forget to include units! Use complete sentences when answering the short-answer/essay questions. Part 1 1. The radius of the sun is 7x105 km, and the speed of light is about 3x105 km/s. How long would it take a photon of light to travel from the center of the sun to the surface if it moves in a straight line, unimpeded? 2. Use the speed of light given in the last question to calculate the length of a light-year in units of kilometers. Knowing that 1 AU equals 8.3 light-minutes, calculate the length of 1 AU in units of kilometers. Check your answers with the values in LU: Appendix A. You will use these conversion factors in later problems. 3. Suppose there are 400 billion stars in the Milky Way Galaxy. How many years would it take to count them if you could count continuously at a rate of one per second? 4. The current US National Debt is estimated to be $9 trillion (1 trillion = 1012). (a) If you laid out enough $1 bills end to end to pay off this debt, how far would the line of dollar bills extend? The length of a $1 bill is 15.5 cm. Give your answer in kilometers, astronomical units, and light-years. (b) Describe in words how far away this is. For example: Between the Earth and the Moon? Somewhere in the solar system? Past the nearest star? 5. The Apollo 11 astronauts made the 380,000 km journey to the moon in only 3 days. How long would it have taken them to get to Mars (75 million km away at closest approach)? To alpha Centauri (4.4 ly away)? 6. Our current fastest spacecraft can travel 50,000 km/hr. How much faster is this than the speed of the Apollo spacecraft? How long would it take one of these “fast” spacecraft to get to Mars? Alpha Centauri? 7. In the “pessimistic” scenario, we used the principle of mediocrity to assume that fl and fi both equal 1 in the Drake Equation. However, 1 is the maximum possible value for both of these terms. What happens to the value of N if we are “cynical” and assume that only 1 in 10 habitable planets can form life and of these only 1 in 100 eventually evolve intelligent life? (Adopt the pessimistic values for the other terms). Is this answer reasonable, or overly pessimistic? Why? Part 2 1. The opening quotation in your book is by Arthur C. Clarke. “Sometimes I think the universe is full of life and sometimes I don’t. Either way is equally amazing.” Do you think the universe is full of life? What about our Milky Way galaxy? Do your answers change if you only consider life that is at least as advanced and intelligent as humans? 2. Describe in your own words the differences between a scientific model, hypothesis, and theory. 3. What is meant by the terms “Occam’s Razor” and “Principle of Mediocrity”? 1
