Stars other than our sun are so far distant that astronomers refer to their distances not in terms of kilometers or miles – but in light-years. Light is the fastest-moving stuff in the universe. It travels at an incredible 300,000 kilometers (186,000 miles) per second. That’s very fast. If you could travel at the speed of light, you would be able to circle the Earth’s equator about 7.5 times in just one second!
A light-second is the distance light travels in one second, or 7.5 times the distance around Earth’s equator. A light-year is the distance light travels in one year. How far is that? Multiply the number of seconds in one year by the number of kilometers (or miles) that light travels in one second, and there you have it: one light-year. It’s about 9.5 trillion kilometers (5.88 trillion miles).
Light travels at 186,000 miles per second.
Therefore 60x60x24x365=seconds in a year 31,536,000 x 186,000 = 5,865,696,000,000 miles in a lightyear.