How would the total amount of insolation change at the equator if Earth's axis was vertical instead of tilted?

How would the total amount of insolation change at the equator if Earth's axis was vertical instead of tilted?

• A. insolation would increase
• B. insolation would decrease
• C. insolation would stay the same
• D. insolation would vary seasonally more

Answer: (A)

The amount of solar energy at a location depends on how high the Sun climbs in the sky and how long it is above the horizon. At the equator today, the Sun’s declination changes with seasons, so the Sun is only directly overhead at noon on a couple of days each year; for part of the year its altitude is lower, which reduces the energy reaching the surface even though day length stays about 12 hours. If the axis were vertical, the Sun would stay directly overhead at noon every day, with the Sun’s path fixed along the celestial equator and roughly 12 hours of daylight year-round. That means a higher average solar elevation and no seasonal dip, so more solar energy would reach the surface on average.