light-years

Would you measure the distance between New York and New Delhi in inches? For the same reason, astronomers don't use miles to measure vast distances in space. Instead, they use light-years: the distance that light travels in a year. That makes Proxima Centauri, the closest known star to the Sun, 4.28 light-years away; that's a lot easier than saying 24,000,000,000,000,000 miles.

Image credits: main image: Eric Hamilton; Mordecai-Mark MacLow: AMNH.