Answer:
We usually use speed of light to measure the distance between two astronomical bodies, because astronomical bodies are very far from each other and we use the light year as the unit of distance for large distances. One light year is the distance covered by light in one year,so the speed of light is the correct option here.
Answer: A. Speed of light.
Have you ever heard a scientist or read an article that said 'x is _ light years away"?
Many people working in the astronomy feild use this term!
