What does it mean that a star is light years away?
A light-year is a unit of distance that measures the distance that light travels in one year in a vacuum. Since light travels at a speed of about 299,792,458 meters per second, one light-year is equal to about 9.46 trillion kilometers (or about 5.88 trillion miles). So when we say that a star is "light-years away," we mean that the distance between us and that star is so vast that it takes light many years to travel that distance. For example, if a star is 10 light-years away from us, it means that the light we see from that star today started traveling towards us 10 years ago. Therefore, we are seeing the star not as it is currently, but as it was 10 years ago. The use of light-years as a unit of distance is particularly useful in astronomy because distances in space are so vast that using kilometers or miles would become impractical.