What is a Light Year?

• A. A unit of time
• B. Distance light travels in one year
• C. The average distance between the Sun and Earth
• D. Distance from Earth to Moon

Answer: (B)

A light year is a distance, not a time. It uses the constant speed of light to define how far light travels in one year in a vacuum. Light moves about 300,000 kilometers per second, so in a year it covers roughly 9.46 trillion kilometers (about 5.88 trillion miles). This huge distance helps us describe how far away stars and galaxies are. It’s far larger than everyday distances like the Earth–Sun distance (about 150 million kilometers) or the Earth–Moon distance (about 384,000 kilometers).