What must happen to the tilt angle of Earth's axis in order to have vertical rays of sunlight strike the surface in Connecticut during the summer solstice (June 21)?

What must happen to the tilt angle of Earth's axis in order to have vertical rays of sunlight strike the surface in Connecticut during the summer solstice (June 21)?

• A. tilt would increase
• B. tilt would decrease
• C. tilt would stay the same
• D. orbit would become more eccentric

Answer: (A)

Vertical sunlight occurs when the Sun is directly overhead at local noon, which happens at the subsolar point. The latitude of that point at the solstices equals Earth's tilt. On the June solstice, the Sun is directly overhead at a latitude equal to the tilt angle. Connecticut sits around 41° N, so to have vertical rays there at noon on June 21, the tilt would need to be about 41°. Since the current tilt is about 23.5°, increasing the tilt moves the subsolar point northward to meet Connecticut’s latitude. If the tilt decreased, the overhead point would move toward the equator; staying the same wouldn’t place the Sun directly overhead over Connecticut at that date. Making the orbit more eccentric changes how far the Earth is from the Sun during the year, not where the Sun is overhead at solstice.

Vertical sunlight occurs when the Sun is directly overhead at local noon, which happens at the subsolar point. The latitude of that point at the solstices equals Earth's tilt. On the June solstice, the Sun is directly overhead at a latitude equal to the tilt angle. Connecticut sits around 41° N, so to have vertical rays there at noon on June 21, the tilt would need to be about 41°. Since the current tilt is about 23.5°, increasing the tilt moves the subsolar point northward to meet Connecticut’s latitude. If the tilt decreased, the overhead point would move toward the equator; staying the same wouldn’t place the Sun directly overhead over Connecticut at that date. Making the orbit more eccentric changes how far the Earth is from the Sun during the year, not where the Sun is overhead at solstice.