It takes the Earth 365 days to complete its revolution around the Sun, and 24 hours to complete its rotation on its own axis. The animation shows how the length of daily light and dark periods varies over the course of a year.
As the Earth moves around the Sun, it spins on its axis at a constant angle. Due to this angle, the Northern and Southern Hemispheres are tilted away from the Sun at opposite points of the year. When a hemisphere is tilted away from the Sun, it experiences winter and longer nights. When a hemisphere is tilted toward the Sun, it experiences summer and longer days.
At the equator, daylight patterns remain fairly consistent throughout the year. The polar regions experience the most extreme patterns of light and dark. During the Southern Hemisphere's winter, the South Pole receives no light at all, while the Northern Hemisphere receives sunlight for 24 hours a day!