The phenomenon responsible for the seasons on Earth is the tilt of the Earth's axis relative to its orbit around the sun. This axial tilt causes different parts of the Earth to receive varying amounts of sunlight throughout the year, leading to the distinct seasonal changes we experience, such as summer and winter. During summer, the hemisphere tilted towards the sun enjoys longer days and more intense sunlight, while winter brings shorter days and less sunlight for the hemisphere tilted away. This variation is crucial for ecological processes and influences climate patterns globally.