The Earth’s Tilt Causes the Seasons
The amount of sunlight on any part of the earth is caused by the earth’s tilt. When the earth is at one end of its path around the sun, the North pole is tilted toward the sun and the south pole is tilted away from the sun. When most of the sun falls upon the northern half of the world, keeping it warm, this causes summer.
At the same time the southern half does not have much light, so it is cool. This causes winter. Once the earth makes a quarter turn around the sun, the amount of sun in the northern part is lighter, it is going into autumn; and the southern part is starting to get more light, so it is going into autumn.