The earth has hotter summers and cooler winters because the axis of the earth is tilted. In July, the earth is tilted on its axis and is the furthest away from the sun while in January it is tilted so that it is closest to the sun at that time of year. That said, during the summer months, due to the way the earth is tilted, the sun's rays hit the earth at a much more direct line meaning they are more powerful. THis, in turn, makes the summer much warmer than the winter.
