Why does latitude matter for insolation?

• A. They have higher sun angles
• B. They have longer days in all seasons
• C. They have lower sun angles and shorter days on average
• D. They are closer to the equator

Answer: (C)

Latitude affects insolation because it controls both the Sun’s height in the sky and how long the Sun is above the horizon. At higher latitudes, the Sun never climbs very high at noon, so the solar rays hit the surface at a low angle. That low sun altitude spreads energy over a larger surface area and means rays travel through more of the atmosphere, which reduces the energy that actually reaches the ground. In addition, day length is shorter on average as you move away from the equator, especially in winter, so there are fewer hours of solar input. Together, these factors lower the average insolation at higher latitudes. Near the equator the Sun is high and daylight is nearly constant, so insolation is higher. In the other choices, the implied mechanisms (higher sun angles, longer days in all seasons, or simply being closer to the equator) don’t correctly describe why latitude changes the amount of solar energy received.