Day and night are caused by the rotation of the Earth on its axis. As the Earth spins, different parts of its surface are exposed to the Sun, creating daylight. When a location rotates away from the Sun, it experiences night. This cycle repeats every 24 hours, resulting in a regular pattern of light and darkness. The length of day and night can vary depending on the time of year and the Earth's tilt. During summer, days are longer, while nights are shorter. Conversely, in winter, nights are longer, and days are shorter. This variation affects climate and ecosystems around the world.