Seasons of the Year

A season is a division of the year, marked by changes in weather, ecology, and hours of daylight.
Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution.^[1] In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to go into hibernation or to migrate, and plants to be dormant.
http://en.wikipedia.org/wiki/Season