Slide 4 of 26
Notes:
The arrows from the left side of this picture are the rays from the sun. These are effectively parallel because the sun is so distant (some 20000 earth radii)
At equinox (September 21, March 21) the axis of rotation of the earth is perpendicular to these rays. At mid-day the sun is then overhead at the equator, and day and night are of equal length throughout the world. However, in the polar regions the sun is barely above the horizon, and its heating effect is very weak. In Madison, where the latitude is 43 degrees, the sun rises to 90 - 43 = 47 degrees at mid-day.
At mid-summer, the axis of rotation is tilted 23 degrees, and the north pole is in perpetual sunlight. The sun in Madison rises to 70 degrees above the horizon, and the intensity of radiation is then almost the same as if it were overhead.