Video narration
If space is full of stars, why is the night sky dark between them? Look up: bright stars, wide black gaps. The stars send light across space, but light passing through it doesn't make space itself glow. On Earth, sunlight hits air and scatters in many directions, brightening the daytime sky. Between stars, there's almost no air to scatter light, so it keeps traveling instead of spilling toward your eyes. But that's only half the answer. The universe hasn't existed forever, so light from every distant star hasn't had time to reach us. As the universe expands-space itself stretches-some light gets stretched beyond what your eyes can see. Because most directions don't end at a star sending visible light to you. Space doesn't scatter it around, and the universe has had only so long to send it.