The phenomenon that causes day and night is the rotation of the Earth on its axis. As the Earth rotates, different parts of the planet are exposed to sunlight while others are in darkness, resulting in the cycle of day and night. This rotation takes approximately 24 hours to complete, leading to the familiar pattern of daytime followed by nighttime. Additionally, this rotation has an impact on the length of daylight during different seasons due to the tilt of the Earth's axis. Understanding this phenomenon is fundamental to our concept of timekeeping and the natural rhythms of life.