Question

As viewed in a city at the Earth's equator, your sunlit standing self does not cast a shadow on the ground when the Sun is at its highest point on the sky on:

A) March 21
B) June 21
C) September 21
D) A and C
E) all of the above

Answer 1

On Earth's equator during the equinoxes on March 21 and September 21, the Sun is at the zenith and one would not cast a shadow at noon. On June 21, the Sun's altitude is 67° above the horizon for equatorial observers, resulting in a shadow.

Step-by-step explanation:

As viewed in a city at Earth's equator, your sunlit standing self does not cast a shadow on the ground when the Sun is at its highest point on the sky on March 21 and September 21. This phenomenon occurs because on these dates, the Sun is on the celestial equator and is directly overhead at noon for observers at the equator, meaning it is at the zenith (90°). On June 21, the Sun is not at the zenith but 23° north of the celestial equator making the Sun's altitude at noon 67° above the horizon, and thus a shadow would be cast.

The correct answer to the question is D) A and C, which corresponds to March 21 and September 21, the dates known as the vernal (spring) and autumnal (fall) equinoxes, respectively.