The phenomenon that explains the formation of seasons on Earth is primarily due to the tilt of the Earth's axis as it orbits the sun. This axial tilt of approximately 23.5 degrees causes varying angles of sunlight to reach different parts of the planet throughout the year. During summer in one hemisphere, that region tilts toward the sun, receiving more direct sunlight and longer days, while during winter, it tilts away, resulting in shorter days and less intensity of sunlight.