The primary reason for the changing seasons is the tilt of the Earth's axis as it orbits the sun. The Earth's axis is tilted at an angle of approximately 23.5 degrees. This tilt causes different parts of the Earth to receive varying amounts of sunlight throughout the year. During summer in the Northern Hemisphere, the North Pole tilts toward the sun, resulting in longer days and warmer temperatures. Conversely, during winter, the North Pole tilts away, leading to shorter days and cooler temperatures. The Southern Hemisphere experiences opposite seasons at the same time, creating a consistent cyclic pattern of seasonal change.