Fast review mode: answers are shown by default so you can skim quickly. Hide them if you want to self-test.
Use the following information for Questions below.
Some of the stars you see in the night sky are so far away from Earth that the light from them has taken millions of years to reach you. So what you are really seeing is what those stars looked like millions of years ago. You are actually seeing into the past. To help us handle these huge distances, we use a special unit of measurement called a light-year to describe them. As its name suggests, a light-year is equal to the distance that light travels in one year. Light travels at 300,000 km per second in the vacuum of space.
Join 4M+ learners. Unlock unlimited quizzes, wrong-answer tracking, flashcards + reminders, study guides, and 1-on-1 challenges.