🌌 Light-years: how big is space?

Unit 1 · Our cosmic neighbourhood · 9 min

Light travels about 300,000 km every second; sunlight reaches us in about 8 minutes. A light-year is how far light goes in a year, about 9.46 trillion km. The nearest star after the Sun, Proxima Centauri, is about 4.2 light-years away; the Milky Way is about 100,000 light-years across. Looking at stars means seeing old light.

Words in this lesson

• 光年 (guāngnián) — light-year
• 恒星 (héngxīng) — star
• 银河系 (yínhéxì) — the Milky Way

Project: Make a cosmic-scale model with a toilet-paper roll: each square is a distance; mark Earth, the Sun and the nearest star (shrink the scale or note what won’t fit).