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Unformatted text preview: ASTR 100: Homework 1 Solutions McGaugh, Fall 2008 1. Problem 1-15. Our solar system is bigger than some galaxies. This statement makes no sense. A galaxy is composed of hundreds of billions of stars, while our solar system is just the stuff orbiting one star, our sun. Our solar system is a tiny part of the Milky Way Galaxy, being much smaller than it. 2. Problem 1-41. Distance by light: The problem asks you to compute the distance that light can travel in different intervals of time, measured in kilometers and miles. d = vt : distance = speed x time. In this case, the speed is the speed of light: v = c . According to Appendix A of the book, c = 3 10 5 km / s. The exact number is c = 299 , 792 km / s; it is OK to use either value. a) 1 light-second = (3 10 5 km / s)(1 s). The seconds cancel out (see Appendix C), so 1 light-second = 300,000 km. 1 km = 0.62 miles, so (300,000 km)(0.62 miles/km) = 186,000 miles. Thats a long way to go in one second! b) Similarly, 1 light-minute = (3 10 5 km / s)(1 minute). Be consistent in the use of units. 1 minute = 60 seconds, so 1 light-minute = (3 10 5 km / s)(60 s). Now the units again cancel nicely, and 1 light-minute = 1 . 8 10 7 km = 1 . 1 10 7 miles....
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