Final answer:
The Sun's rays are perpendicular to Earth's surface at the equator during the March Equinox and the September Equinox.
Step-by-step explanation:
The Sun's rays are perpendicular to Earth's surface at the equator during the March Equinox and the September Equinox.
On these dates, the Sun crosses the celestial equator, which passes through the zenith at the equator. This means that at noon, the Sun appears directly overhead at 90°, creating perpendicular rays.