Final answer:
The Tropic of Capricorn receives the direct vertical rays of the sun on December 21 or 22 during the Southern Hemisphere's summer solstice and the Northern Hemisphere's winter solstice, due to Earth's 23.5-degree tilt.
Step-by-step explanation:
The vertical rays of the sun strike the earth at the Tropic of Capricorn on approximately December 21 or 22. This event marks the winter solstice in the Northern Hemisphere and the summer solstice in the Southern Hemisphere. It is a result of the Earth's tilt of 23.5 degrees, which leads to seasonal variations as the Earth orbits the Sun.
During this time, the North Pole experiences 24 hours of darkness while the South Pole enjoys continuous daylight, known as the midnight Sun. Observers located precisely on the Tropic of Capricorn (23.5 degrees south of the equator) will see the Sun pass through the zenith at noon, leading to the longest day of the year in the Southern Hemisphere and the shortest in the Northern Hemisphere.