Why do shooting stars happen so high up?
Space dust starts glowing as soon as it hits enough air, about 80 to 120 kilometres up, and tiny grains burn away before getting any lower.
Shooting stars glow far above us, usually between about 80 and 120 kilometres up. That is around ten times higher than aeroplanes fly. Why so high?
Earth's air gets thinner and thinner the higher you go. Very high up, there is hardly any air at all. A speck of space dust zooming in from space meets almost nothing at first. But by about 100 kilometres up, there is just enough air for the dust grain to start crashing into air molecules. Because it is moving so fast, these crashes heat the air around it until it glows. That is when we see a shooting star.
Most shooting star grains are tiny. They burn away in less than a second, long before they get anywhere near the ground. So the whole light show happens in the thin upper air.
Bigger space rocks can push deeper into the air before they stop glowing, sometimes down to 20 or 30 kilometres up. The biggest might reach the ground as meteorites.
The layer of air where shooting stars happen is called the mesosphere and the bottom of the thermosphere. It is so high that shooting stars over one country can be seen by people hundreds of kilometres away.