Earth rotates about its polar axis as it revolves around the Sun. Earth's polar axis is tilted 23.5° to the orbital plane (ecliptic plane). Combinations of rotation, revolution, and tilt of the polar axis result in differential illumination and changing illumination patterns on Earth. These changing patterns of illumination result in differential heating of Earth's surface that, in turn, creates seasonal climatic and weather patterns.

Earth's rotation results in cycles of daylight and darkness. One daylight and night cycle constitutes a diurnal cycle. Daylight and darkness are separated by a terminator—a shadowy zone of twilight. Earth's rate of rotation—approximately 24 hours—fixes the time of the overall cycle (i.e., the length of a day). However, the number of hours of daylight and darkness within each day varies depending upon latitude and season (i.e., Earth's location in...