Photoperiod

Photoperiod is the change of day length over the seasons. Earth's rotation around its axis produces 24-hour changes in light (daytime) and dark (night) cycles on Earth. The length of the light and dark in each phase varies across the seasons due to the axial tilt of Earth. The photoperiod defines the length of the light. For example, in summer the length of light could be 16 hours while the dark is 8 hours, whereas in winter the length of day could be 8 hours, while the dark is 16 hours. Importantly, the axial tilt of the Earth causes the opposing seasons in the Northern and Southern Hemispheres.