Science Puzzle
What Is a Shooting Star?
On a clear, dark night, especially in mid-August, you may see a streak of light dart across the sky and vanish in about a second. People call it a shooting star.
What is a shooting star really?
The Answer
A tiny speck of space dust or rock, usually no bigger than a grain of sand, hitting the top of the atmosphere so fast that it heats up and burns away in a flash. Its proper name is a meteor.
Real stars are suns, so enormous and far away that one could never fall to Earth. A meteor is the opposite: a crumb. What makes it so bright is its speed. It meets the air at somewhere between 11 and 72 kilometres a second, dozens of times faster than a rifle bullet. It squeezes the air in front of it so violently that the air heats to thousands of degrees, and the speck glows and vaporises about 80 to 120 kilometres up, leaving a trail of glowing gas. It's the squeezing of the air, more than rubbing against it, that does the heating.
Most of these specks are dust shed by comets. When Earth passes through a comet's trail of dust, we get a meteor shower. The Perseids, every August, come from Comet Swift-Tuttle, and at their peak you can see dozens an hour from a dark place.
Bigger chunks sometimes survive the fall and land as meteorites, but nearly all shooting stars burn up completely, high above our heads.
The principle: Heating by compression. A speck of space dust hitting the air at tens of kilometres a second squeezes the air in front of it so hard that both glow, and the speck burns up high above us.