According to the National Aeronautics and Space Administration (NASA), a light year is, “The distance light travels in 1 year.” How far is that, really, and how do we figure it out?
First, we must understand that we're talking about distance not time. We already know the time, how long it takes to travel from 1 place to another, 1 year. Distance refers to how far it is from one point to another. If the doctor's office is 2 miles from your house, the distance is 2 miles.
Scientists determined that light travels at a rate, or speed, of 186,287.5 miles in 1 second. With that information, we can figure out how far light travels in 1 year.
There are 60 seconds in 1 minute. So, if we multiply the speed of light by 60, we'll know how fast light travels in 1 minute. To figure out how far light travels in 1 hour, we need to know that there are 60 minutes in 1 hour. So, we'll do the same thing again. If we multiply our new answer by 60 minutes, we'll find out how many miles light travels per hour.
Now let's figure out how far light travels in 1 day. There are 24 hours in a day, so if we take our answer and multiply that by 24, we end up with miles per day. This is where it gets a little tricky! We have Leap Year every 4 years for a reason. It takes us 365 days and 6 hours to complete 1 revolution around the Sun. We know that 6 hours equals 1/4 or .25 of a day. Rather than beginning the New Year at 6 o'clock in the morning one year, noon the next, 6 o'clock in the evening on the third, midnight on the fourth, and starting the cycle again the fifth year, the experts added 1 day, which is 29February, every 4 years to help balance it out. Why does this matter to us? Well, when we figure out the distance light travels in 1 year, we must remember to add in that 1/4 day; otherwise, our answer won't be accurate.
When we take the answer we found last time and multiply that by 365, we get 5,874,762,600,000. Then, we need to multiply the same miles per day times our remaining 1/4 day. Since it's easier to use decimals, we'll use .25. This gives us 4,023,810,000 miles per 1/4 day. Now, all we need to do is add these 2 totals together. When we do, we get 5,878,786,410,000 miles per year. So, a light year is equal to almost 6 trillion miles.