7 of 8

LESSON 5 · Physics in the Real World

Space Is Black

Above the atmosphere, there is no air to scatter sunlight. Photons from the Sun travel in straight lines without bouncing off molecules.

Astronaut photos from the ISS show this dramatically — a brilliant blue Earth below, the thin bright band of atmosphere along the horizon, and pitch-black space above. The Sun blazes impossibly bright, but the sky around it is dark.