Astronomy Today

Measuring Units

What is a light-year?

A light-year is the distance a beam of light travels through the vacuum of space in one Earth year. Because light in a vacuum travels at about 186,000 miles (300,000 kilometers) per second, and because are about 31,500,000 seconds in a year, a light-year is about 5.88 trillion miles (9.47 trillion kilometers).


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