Sunrise and sunset times change throughout the year because the Earth is tilted on its axis. Due to this tilt, the sun is visible for slightly different lengths of time each day, resulting in the observed changes in sunrise and sunset.
For residents of the Northern Hemisphere, the longest day occurs on the June Solstice, while the December Solstice is the shortest day of the year. In the Southern Hemisphere, the June Solstice is the shortest day of the year, and the December Solstice is the longest. The Earth’s tilt is also responsible for longitudinal variations in day length. Day length varies greatly near the poles and is more consistent in tropical regions.