Seasons - Solar Intensity Panel

The Solar intensity panel, shown to the left, illustrates what happens to a "beam of sunlight" as the earth orbits the sun. This is one of the primary causes of the seasons (not how close the earth is to the sun!).

As the altitude of the sun decreases, a constant beam of sunlight gets spread out over a larger area. Thus, the energy has to be spread over a larger area, so each square receives less energy.

As the altitude of the sun increases, the constant beam of sunlight gets more concentrated. Thus, there is more energy per square.

Notice that, as this animation portrays it, on the first day of summer the beam is "circular". This would only be the case if the sun were directly overhead. At more northerly latitudes, this beam pattern does become more concentrated, but never circular.

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