The main reason for seasons on Earth is the axial tilt of the planet. Earth is tilted at an angle of approximately 23.5 degrees relative to its orbital plane around the sun. This tilt causes different parts of the Earth to receive varying amounts of sunlight throughout the year. As the Earth orbits the sun, the northern and southern hemispheres experience changes in seasons—when one hemisphere is tilted toward the sun, it experiences summer, while the opposite hemisphere, tilted away, experiences winter. This variation in sunlight and temperature defines the seasonal cycles we experience each year.