define latitudes.

distinguish diffrent heat zones of earth???

In geography, latitude is a geographic coordinate that specifies the north-south position of a point on the Earth's surface. Lines of constant latitude, or parallels, run east–west as circles parallel to the equator. Latitude is an angle (defined below) which ranges from 0° at the Equator to 90° (North or South) at the poles.

Latitude is used together with longitude to specify the precise location of features on the surface of the Earth. Since the actual physical surface of the Earth is too complex for mathematical analysis two levels of abstraction are employed in the definition of these coordinates. In the first step the physical surface is modelled by the geoid, a surface which approximates the mean sea level over the oceans and its continuation under the land masses. The second step is to approximate the geoid by a mathematically simpler reference surface. The simplest choice for the reference surface is a sphere, but the geoid is more accurately modelled by an ellipsoid. The definitions of latitude and longitude on such reference surfaces are detailed in the following sections. Lines of constant latitude and longitude together constitute a graticule on the reference surface. The latitude of a point on the actual surface is that of the corresponding point on the reference surface, the correspondence being along the normal to the reference surface which passes through the point on the physical surface. Latitude and longitude together with some specification of height constitute a geographic coordinate system as defined in the specification of the ISO 19111 standard.

There are 4 major climate zones:

• Tropical zone from 0°–23,5° (between the tropics)
  
In the regions between the equator and the tropics (Equatorial region) the Solar radiation reaches the ground nearly vertically at noontime during almost the entire year. Thereby, it is very warm in these regions. Through the high temperatures, more water evaporates, so that the air is often moist. The resulting frequent and dense cloud cover reduces the effect of solar radiation on ground temperature .


• Subtropics from 23,5°–40°
The subtropics receive the highest radiation in the summer, since the sun's angle at noon is almost vertical to the earth, whilst the cloud cover is relatively thin. These regions receive less moisture (see Trade winds), and that increases the effect of radiation. Therefore,  most of the deserts in the world are situated in this zone. In the winter,  the radiation in these regions decreases significantly, and it can be temporarily very cool and moist . 


• Temperate Zone from 40°–60°
In the temperate zone, the solar radiation arrives at a smaller angle, and the average temperatures here are much cooler than in the subtropics. The seasons and daylength differ significantly in the course of a year. The climate is characterised by less frequent extremes, a more regular distribution of the precipitation over the year and a longer Vegetation period - therefore the tame "temperate".


• Cold Zone from 60°–90°
The polar areas between 60° latitude and the poles receive least heat through solar radiation, since the sun has a very flat angle to the ground. Because of the changes of the earth axis angle to the sun, the daylength  varies most in this zone. In the summer, polar days occur. The Vegetation  is only possible during few months per year and even then often sparsely. The conditions for life in these regions are very hard.