What the affects the angle at which the suns rays hit earth?
The light from the sun travels in a straight line, and we can
assume the light rays to be parellel. The angle of incidence on the
earths rounded surface depends on where you are on the earth and
what time it is. Mid-day on the equator and the rays would hit the
ground straight on. Further to the north or south, or later/earlier
in the day and the light rays would hit at more of angle. The rays
would also have to penitrate more of the earths atmosphere as the
angle increases, which takes more `strength` out of the sun.