Earth's axis is an imaginary line that runs from the North Pole to the South Pole. It is tilted at an angle of about 23.5 degrees relative to its orbit around the Sun. This tilt is responsible for the changing seasons as different parts of the Earth receive varying amounts of sunlight throughout the year. The axis also plays a crucial role in the concept of day and night. As the Earth rotates on its axis, different areas are exposed to sunlight, creating daytime, while the areas facing away from the Sun experience nighttime. This rotation takes approximately 24 hours to complete.