Day length refers to the duration of time from sunrise to sunset. It varies throughout the year due to the tilt of the Earth's axis and its orbit around the Sun. In summer, days are longer, while in winter, they are shorter. Different locations on Earth experience varying day lengths. For example, regions near the Equator have relatively consistent day lengths year-round, while areas closer to the Poles can experience extreme variations, such as continuous daylight in summer and prolonged darkness in winter. This phenomenon is known as the midnight sun and polar night.