Light year

A light year (symbol: ly) ^[1] is the distance that light travels in empty space in one year. Since the speed of light is about 300,000 km per second (about 186,000 miles per second), then a light year is 9.46 trillion kilometers (about 5.87 trillion miles), for AU, one light year is 63,241 AU.^[2] A light year is not a length of time.

The light year is used in astronomy because the universe is huge. Space objects such as stars and galaxies may be hundreds, thousands or millions of light years away.

1. ↑ or light-year or lightyear
2. ↑ The IAU and astronomical units, International Astronomical Union, retrieved 2008-07-05