The reason why temperature changes during the seasons is due to the way the Earth moves. The part of the Earth that is facing the sun changes throughout the year. The warm temperatures found on the Earth come from the heat of the sun. The Earth rotates as it orbits the sun. As the Earth moves, it will lean more directly against the sun. The sun rays that hit the Earth will be a smaller angle in some parts of the world than others. When the light from the sun is spread over a larger surface of the Earth, the Earth gets less heat. At the same time, the other part of the world will be getting more concentrated rays, meaning it will be hotter when the opposite side is cooler.

Reasons for Seasons
The four seasons happen because of the tilt of the Earth's axis. At different times of the year, the sun's rays hit different parts of the globe more directly. The angle of the Earth's axis tilts the Northern Hemisphere towards the sun during the summer.