Light Years
Distances in space are huge, so scientists devised several different ways to measure distance with numbers that are manageable. A light year is defined as being the distance light will travel through a vacuum in one year, which is 9,460,530,000,000 kilometers (or, if you prefer, 5,878,000,000,000 miles). Light only takes about 5.5 hours to cross our solar system, so in terms of the big picture you can see that our solar system is actually quite small. Other than the Sun, the closest star to us is Proxima Centauri, which is about 4¼ light years away -- which is a big distance indeed, compared to the size of the solar system. Voyager 1, an unmanned space probe, was launched on September 5, 1977; at the moment, it is fractionally more than 13 light hours from Earth. Now you can begin to appreciate the distance in a light-year!
