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Solar System
Space and Stars

What Is a Light-year?

What Is a Light-year?
Reading Level
     edHelper's suggested reading level:   grades 5 to 8
     Flesch-Kincaid grade level:   5.21

Vocabulary
     challenging words:    humongous, light-year, light-years, trillion, measurement, unit, measure, distance, travels, although, space, such, between, difficult, number, reason
     content words:    Proxima Centauri

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What Is a Light-year?
By Cindy Grigg 		  
1     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.
 
2     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.
 
3     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.

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