The sun is the main source of power and heat on the planet. Falling on the Earth's surface, the ray of sunlight starts a set of the vital processes, for example, photosynthesis in plants. A hade in various places different therefore heating happens up to the different temperature.
The concept of climate, namely classification of thermal and climatic zones is connected with the phenomenon of different extent of heating of the earth's surface in various areas. The word climate comes from Greek klimatos - "inclination". The climate depends on a geographical location of a certain area and is defined by the average annual temperature, humidity and atmospheric pressure. Allocate three main types of thermal belts: cold, moderate and hot. The frigid zone is in area of a polar circle which is located in each of two hemispheres of Earth, Northern and Southern. The fact is that poles are extremely removed from the equator and consequently, receive only slanting sunshine which heat the earth very poorly. Several months in a year sunshine in general there do not reach, this period is called polar night. Temperature in polar night can fall to - 89 wasps. The moderate thermal belt means average climate and also is in each of two terrestrial hemispheres. The northern moderate belt passes between Arctic Circle and the Tropic of Cancer, and Youzhny – between the Antarctic Circle and the Tropic of Capricorn. The Tropic of Cancer and the Capricorn are two from five main parallels of the globe, they are located specularly in relation to the line of the equator. In a moderate belt the slanting sunshine poorly heat the earth in the winter, and more direct – in the summer. In a hot thermal belt there is always a high temperature as the sun always rises highly and sends to the earth direct beams. This belt dominates in the tropics which are close located to an equator zone. The winter in hot climate is served by a rainy season, and a role of summer – a drought season. Thus, Earth is surrounded by five thermal belts. Sometimes in a zone of the frigid zone allocate the extreme area called area of an eternal frost where average annual temperature never exceeds 0 wasps. Such areas directly surround poles, and the area of the frigid zone lies in subpolar latitudes, namely in a zone of the tundra.