For general reference, there are 63,000 astronomical units in one light-year, and 63,000 inches (160,000 cm) in one mile (1.6 km). One arcsecond is equal to 3.26 light-years. Like degrees, the light-year can also be broken down into smaller units of light-hours, light-minutes or light-seconds. In February 2017, astronomers detected seven Earth-sized planets orbiting a single star 40 light-years away from Earth. As we established above, light travels 9,460,528,000,000 km in a year. One light year is 186000 X 60 X 60 X 24 X 365 miles Putting that into perspective, the duration of recorded human history is roughly 5,000 years. A light year is the distance light travels in 1 human year. It's exciting news, but it begs the question: just how far away is that? 1 year. How far is 40 light-years?