Day and night on Earth are caused by the planet's rotation on its axis. Earth spins around an imaginary line called its axis, which runs from the North Pole to the South Pole, completing one full rotation approximately every 24 hours. When a part of the Earth faces the Sun, it experiences daylight; when it rotates away from the Sun, that part experiences nighttime

. This rotation makes the Sun appear to rise in the east and set in the west. At any given time, half of the Earth is illuminated by the Sun (daytime), while the other half is in darkness (nighttime). As Earth rotates, different areas move into and out of sunlight, creating the cycle of day and night

. Additionally, the Earth's axis is tilted about 23.5 degrees relative to its orbit around the Sun. This tilt causes variations in the length of day and night throughout the year and is responsible for the changing seasons, but the fundamental cause of day and night remains the Earth's rotation

. In summary, the cycle of day and night results from the Earth spinning on its axis, causing alternating exposure to sunlight and darkness as different parts of the planet face toward or away from the Sun.