In space, the Earth's position at any point in a year is the factor that causes the Season.
The position of earth determines the ray of sunlight that falls upon the earth surface. When the earth tilts towards the sun with the north pole facing sun the north pole region experience the summer season while south pole region undergoes the winter season in the same time and vice versa.
So, seasons are changed with the interval because of the rotation of the earth towards the sun.
