What causes our planet to have four seasons.?
The tilt of the earth, as others have said, moderates how much sunlight and therefore how much energy parts of the world receive. The sun is the furthest North in June and furthest South in December. The seasons lag slightly behind each solstice because it takes a while for earth and water to absorb all of the energy. The four seasons you think of only exist in the middle latitudes of both hemispheres – the temperate regions from about 30 – 55 degrees. In the tropics, the only noticeable seasonal change is the yearly monsoon, a low pressure shift that causes a rainy season. In the polar regions, there are really only two seasons – a bitter, dark subzero winter and a less cold and sunny summer.
