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Unformatted text preview: Astronomy C10 / L&S C70U: Fall 2010 Homework #1 Solutions Maximum points possible = 50 1. PF, p. 20, Q2 (2 + 2 = 4 points total). Here, we just need to keep track of units. (a) (2 points.) c = (3 × 10 5 km / sec)(10 3 m / km) = 3 × 10 8 m / sec . (b) (2 points.) c = (3 × 10 8 m / sec)(10 2 cm / m) = 3 × 10 10 cm / sec . [Note to graders: 1 point off each part if no work is shown (i.e., only the answer is given).] 2. PF, p. 20, Q3 (4 points). Light travels at a finite speed, so the farther away an object is from us, the longer the light takes to reach us. When we detect the light, we are seeing the object as it was in the past. For example we see the Sun as it was about 8 minutes ago, the nearest star as it was about 4 years ago, and the Andromeda galaxy as it was about 2.4 million years ago! Astronomers are now able to detect extremely distant galaxies in their early stages of formation, when they and the Universe were very different from how they are today. These are pictures of an era billions of years into the past. This light first started its journey long before humans existed, before the dinosaurs ruled, or even before the Earth was formed! [Note to graders: Students need not have included examples, for full credit.] 3. Scientific notation (2 + 2 + 2 = 6 points total). With scientific notation , we place only one digit to the left of the decimal point, and multiply the number by a power of 10 such that it gives an number equivalent to the one you started with. A good way to do this is to count the number of places we have to move the decimal, then use that number as the power of your 10. For instance, if you count three spaces to the left, that will be 10 3 , or 1000. If you count 3 to the right, you have 10 3 . Let’s put this into practice. (a) (1 + 1 = 2 points.) 45097.11 = 4 . 509711 × 10 4 ; 6604 = 6 . 604 × 10 3 (b) (1 + 1 = 2 points.) 0.002678 = 2 . 678 × 10 3 ; 0.0556 = 5 . 56 × 10 2 (c) (1 + 1 = 2 points.) 6 . 68 × 10 6 = 0.00000668 ; 5 . 31 × 10 4 = 53100 [Note to graders: Give 0 points if not all digits are listed in a given answer, since the answers should be exact.] 1 4. PF, p. 20, Q7 (3 points each part; 15 points total)....
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 Fall '10
 FILIPPENKO
 Light, Speed of light, Astronomical unit, Lightyear

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