Night and day occur as Earth rotates around its axis. It takes Earth slightly under 24 hours to complete a full rotation, thus the 24-hour day. Earth rotates around its axis at a speed of 1,040 mph, allowing the entire circumference to rotate 360 degrees.
The length of day and night vary throughout the year based on the tilt of Earth in relation to the sun. During winter in the United States, the Northern Hemisphere tilts away from the sun and is exposed to the sunlight for a shorter period of time. The shallower angle of sunlight accounts for winter's lower temperatures. The North Pole tilts almost completely away from the sun then, giving the area a months-long night. During summer, the opposite occurs as the Northern Hemisphere receives longer periods of light from the sun, leading to longer days and shorter nights. During this part of the year, the North Pole receives constant daylight. Rotation around an axis is a feature common to all planets, all of which also experience days and nights of varying lengths. For example, a day on Mercury takes 58 Earth days and 15 hours, while a day on Uranus takes only 17 hours and 14 minutes.