A light-year describes how far light travels in a year. The calculation is reached by multiplying the speed per second with the number of seconds in a year. The speed of light is about equal to 186,000 miles per second. Since there are 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, and 365 days in a year, the equation would be:

186,000 x 60 x 60 x 24 x 365=5,865,696,000,000 or about 6 trillion