Nighttime is not an active physical phenomenon but a perceptual one. It is the result of the geometric relationship between the Sun, Earth, and an observer on Earth’s surface. Specifically, night occurs when a hemisphere of Earth is rotated away from the Sun, causing the local sky to fall within the planet’s own shadow.

The Astronomical and Geophysical Causes of Nighttime

Nighttime is fundamentally a . It occurs because Earth is a rotating, opaque sphere, and the Sun’s light cannot pass through it. When your location on Earth turns away from the Sun, you experience night.