See how many you can count while gazing up at the sky on a clear night. Not only are there too many stars to count , but the distances between us and the stars are beyond our imagination. Therefore, scientists use a unit known as the light year . A light year is defined as the distance that light travels in one Earth year. In one second light can travel around Earth almost four times.
Nothing travels faster, establishing light as the ultimate speed limit.
This distance equals one light year. Because light travels so very fast, everything appears to happen instantly in our everyday experience. If we are watching the Baltimore Ravens kick a field goal, we assume that the ball is kicked right at the moment that we see it. In actuality we see the light that is being reflected from the ball, and it does take time for the light to travel from the ball to our eyes. Stars are millions and millions of kilometers away.