Final answer:
The Bahamas and Saudi Arabia will see the sun directly overhead on the summer solstice, around June 21, because the tilt of the Earth's axis on that day causes the Northern Hemisphere to be most tilted towards the sun.
Step-by-step explanation:
The days when the sun will be directly overhead at specific locations such as the Bahamas and Saudi Arabia depend on the latitude of these places in relation to the Earth's tilt and orbit around the sun.
The Bahamas, being close to the latitude known as the Tropic of Cancer, will experience the sun at the zenith—the highest point in the sky—on or about June 21, which is the date of the summer solstice in the Northern Hemisphere. On that day, the sun appears directly overhead at noon for locations at approximately 23° N latitude. This is because the tilt of the Earth's axis is such that the Northern Hemisphere is most tilted towards the sun.
As for Saudi Arabia, which also lies near the Tropic of Cancer, the situation is similar, and residents will see the sun directly overhead on the summer solstice as well. The equinoxes, which occur around March 21 and September 21, are when the sun is on the celestial equator. During this time, every place on Earth experiences roughly equal amounts of day and night as the sun favors neither hemisphere.
Therefore, the correct answer is a) Summer solstice for when the sun will be directly overhead at both the Bahamas and Saudi Arabia.