Day and night are the two main phases of a 24-hour cycle on Earth. Day occurs when the side of the planet facing the Sun receives sunlight, making it bright and warm. This light allows people and animals to see and be active. Night happens when the Earth rotates, causing the opposite side to be away from the Sun. During this time, it becomes dark and cooler. Many creatures rest or sleep, while others, like nocturnal animals, become active. The cycle of day and night is essential for life on Earth, influencing behaviors and natural processes.