The climatic zones of the earth are defined by the different amounts of sunlight received in the various latitudes.

The intensity of solar radiation is depending on the angle at which the solar rays are hitting the earth. At the days of equinox, the solar rays are hitting the equatorial region directly from above, the poles, in contrast, only laterally. The equatorial region receives more solar radiation when compared to the poles. Due to the inclination of the terrestrial axis, the amount of radiation received by a given place is changing in the course of a year, resulting in the various seasons.