You will be given a definition of a task first, then some input of the task.
Given a scientific passage and an answer, generate a question for the given answer.

Passage: Viewing distant stars is looking back in time. The stars we see are many thousands of light years away, which means the light takes many thousands of years to reach us. Thus the stars we see in the sky are how they looked thousands of years ago. Answer: light years
Output:
The distance of stars is measured in what terms, meaning the light takes many thousands of years to reach us?