The hypothetical climate that would prevail on a uniform solid earth with no atmosphere. Thus, it is a climate of temperature alone and is determined only by the amount of solar radiation received, that is, determined by the elevation of the sun as it varies with season. Solar climatic zones, therefore, are parallel to lines of latitude. The solar climate and the nearly synonymous mathematical climate have both grown out of the earliest approach to climatology, as is indicated by the fact that “climate” takes its name from the inclination (Greek klima) of the sun's rays.