What causes the change of seasons

The four seasons happen because of the tilt of the earth axis. During different times of the year, the rays of the sun hit different parts of the earth more directly. The angle of the earth's tilts the northern hemisphere towards the sun during summer season while the southern hemisphere is tilted away causing winter. Without the tilt of earth, there would be no seasons. Regions along the equator would be always be warm and sunny while those in the southern and northern hemisphere would be stuck in a gradual gradient of cold and hot.