The phenomenon responsible for the change of seasons on Earth is primarily the tilt of the Earth's axis and its orbit around the Sun. As Earth revolves around the Sun, different parts receive varying amounts of sunlight throughout the year, leading to seasonal changes. During summer, the hemisphere tilted towards the sun experiences longer days and warmer temperatures, while the opposite hemisphere undergoes winter. This axial tilt is approximately 23.5 degrees, which is significant in creating the seasons we experience.