A light-year is the distance that light travels in one year.

the speed of light is 299,792,458 metres per second which is about 670.6 million mph

Alpha Centtauri is 4.37 light years away so if you were to travel at the speed of light it would take you 4.37 years to get there from earth.

light travels 5,874,589,152,000 miles per year

The Challenger space shuttle was recorded as going about 18,000 mph. Which means it would travel 157,680,000 miles per year. that means for the challenger to travel one light year it would take 37,256 years for a man made machine to travel one light year.