What is a light year?

A light year is a way of measuring distance, and astronomers use light years to measure the distances between stars. It is the distance that light travels in one year, and is equal to almost 5.9 trillion miles (9.5 trillion kilometers). To think about how long a light year is, consider this: The Sun is about 93 million miles (149 million kilometers) from Earth, and a person would have to travel 31,620 round trips from Earth to the Sun to travel the distance of a light year. Scientists can see things in the universe more than 15 billion light years away.