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A light-year
"What is a light year?"
A light-year is a unit of distance. It is the distance that light can travel in one year. Light
moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can
travel about 10 trillion km. More p recisely, one light-year is equal to 9,500,000,000,000
kilometers or about 5,878,630,000,000 miles.... So, this distance is 1 light-year. ...
The fastest thing that we know of is light which travels at a speed of 186,000 miles or 300,000
kilometers per second in empty space. To get an idea of how fast this is, light can travel about seven
times around Earth in one second! Astronomer use the speed of light to measure how far away things
are in space. They use a unit called the light-year. A light-year (ly) is the distance that light can travel in
one year. In one year light travels about 5,880,000,000,000 miles or 9,460,000,000,000 kilometers. So,
this distance is 1 light-year. For example, the nearest star to us is about 4.3 light-years away. Our
galaxy, the Milky Way, is about 150,000 light-years across, and the nearest large galaxy, Andromeda, is
2.3 million light-years away.