21st June
Explanation
The apparent movement of the Sun relative to the Earth is governed by the Earth's revolution around the Sun and the tilt of its axis ($23.5^\circ$). This results in the migration of the vertical rays of the Sun between the Tropic of Cancer and the Tropic of Capricorn throughout the year.Analysis of Dates:
- 21st June (Summer Solstice): On this date, the Northern Hemisphere is tilted towards the Sun. The rays of the Sun fall directly on the Tropic of Cancer ($23.5^\circ$ N). This marks the longest day in the Northern Hemisphere.
- 21st March and 23rd September (Equinoxes): On these dates, the Sun is vertically overhead at the Equator. All places on Earth experience equal days and nights.
- 22nd December (Winter Solstice): On this date, the Southern Hemisphere is tilted towards the Sun. The rays of the Sun fall directly on the Tropic of Capricorn ($23.5^\circ$ S).
Key Takeaway: The Tropic of Cancer receives direct solar insolation on the Summer Solstice, which occurs on 21st June.