The first people to fly

On this day in 1783, two men climbed aboard a huge balloon in Paris and floated up into the sky, the first people ever to fly freely. A fire beneath the balloon kept the air inside it warm, and Benjamin Franklin, who lived nearby, watched them rise and drift away over the city.

Why it mattered

Warm air is lighter than the cool air around it, so a balloon full of it rises. That simple idea carried the first people up into the sky.