The angle at which the sun's rays strike the surface of the Earth is determined by……. .

Rays of sunlight travel from 150 million kilometres away, and when they reach the Earth, they are parallel rays. The curve of the Earth means that the rays are vertical at the Equator but at quite a low angle when they reach temperate latitudes. As the rays lose heat passing through the atmosphere, the more direct the journey, the greater the heat which penetrates through to the surface of the Earth. The vertical rays in equatorial latitudes mean that it is much hotter at the Equator than it is in the regions where the sun's rays strike at a low angle. It is these variations in temperature that are largely responsible for the changes in weather.