Final answer:
On March 21, the spring equinox, the direct rays of the sun fall on the Equator. This happens when day and night are roughly equal in duration worldwide, unlike on the solstices when the Tropic of Cancer or Tropic of Capricorn receive direct sunlight.
Step-by-step explanation:
On March 21, also known as the spring equinox, the direct rays of the sun fall on the Equator. During an equinox, the Earth's axis is not tilted toward or away from the Sun, leading to an event where day and night are approximately equal in length all over the world. The Earth's tilt is at 23.5 degrees, and the Tropic of Cancer and the Tropic of Capricorn mark the farthest north and south latitudes where the sun can be directly overhead. However, only during the equinox does the Equator experience the Sun at the zenith, thus, receiving the direct rays of the Sun.
Additionally, on the June and December solstices, the Tropic of Cancer and Tropic of Capricorn, respectively, receive direct sunlight. The Arctic Circle is the latitude point north of which the sun can be seen for 24 continuous hours at least once per year, typically on the summer solstice.