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Transcript
What Is a Light-year? By Cindy Grigg On Earth, we measure distance in inches or centimeters, yards or meters, miles or kilometers. But space is vast and distances between stars or galaxies are humongous. Scientists need something bigger to measure such distances. 1 Astronomers measure distances in light-years. Although "light-year" sounds like it measures time, it doesn't. A light-year is the distance light travels in one year. 2 What is the nearest star to Earth? Our sun is the nearest star. It is about 150,000,000 km away. The next closest star to Earth is Proxima Centauri. Proxima Centauri is 40 trillion (40,000,000,000,000) kilometers from Earth. Such a large number is difficult to understand and use in calculations. For this reason, astronomers use a different unit of measurement when they talk about distances between stars. 3 In one year, light travels 9.5 trillion km. If there were a star 9.5 trillion km from Earth, it would take one year for its light to reach us. By the time the star's light reached us, the light would be a year old. Looking at stars is a little like looking back in time. 4 So how far away is Proxima Centauri in light-years? To find the answer, divide the distance from Earth to Proxima Centauri (40 trillion km) by the distance in one light year (9.5 trillion km) The answer is 4.2 light-years. 5 Copyright © 2015 edHelper Name _____________________________ Date ___________________ What Is a Light-year? 1. Why do scientists measure distance in light-years? A light-year is shorter than other measurements. They need a bigger unit to measure large distances. Since they're measuring distances between stars, they need to measure light. They like to confuse people. 3. What is the closest star to Earth? 2. How did the light-year get its name? It was named for the time it takes light to travel in one year. It was named for the distance that light travels in one year. It was named for a scientist named Light. It was named because someone thought it was pretty. 4. How long does it take light to travel to Earth from Proxima Centauri? 40 years 150 years 4.2 years 9.5 trillion years 5. If a star was 19 trillion km from Earth, how long would it take for its light to reach us? 200 years 5 years 20 years 2 years 6. A light-year is the distance that light travels in one year. False True 7. Proxima Centauri is the name of a galaxy. 8. In one year, light travels 9.5 billion km. False True False True Name _____________________________ Date ___________________ What Is a Light-year? 9. Andromeda is the closest star to Earth after the sun. False True 10. According to the reading passage, which of the following is probably true? The sun's light takes one light-year to reach Earth. Proxima Centauri is closer to Earth than the sun is. The light that reaches Earth from distant stars is very old. Scientists disagree about using light-years to describe distances in space. What Is a Light-year? - Answer Key 1 They need a bigger unit to measure large distances. 2 It was named for the distance that light travels in one year. 3 the sun 4 4.2 years 5 2 years 6 True 7 False 8 False 9 False 10 The light that reaches Earth from distant stars is very old. Return to edHelper.com What Is a Light-year? Reading Comprehension Reading comprehension Puzzles using Word List Word Search Word Search (PDF and options) Make Words Word building activity Word building activity (with word search) Word Shapes Word Shapes (easier - one letter filled in) Word Shapes (fill in word shapes and also write the word) Word Shapes