21st June
Explanation
The variation in the length of day and night across the globe is determined by the Earth's revolution around the Sun and the inclination of its axis. Specific dates mark the extreme positions of the Earth relative to the Sun, known as Solstices.- 21st June (Summer Solstice): On this date, the Sun is vertically overhead at the Tropic of Cancer ($23.5^\circ$ N). Consequently, the Northern Hemisphere receives maximum insolation and experiences the longest day and the shortest night of the year.
- 22nd December (Winter Solstice): The Sun is vertically overhead at the Tropic of Capricorn ($23.5^\circ$ S). The Northern Hemisphere experiences the shortest day and the longest night.
- 21st March and 23rd September (Equinoxes): On these dates, the Sun is vertically overhead at the Equator. All places on Earth experience equal lengths of day and night (12 hours each).
Key Takeaway: The Summer Solstice occurs on 21st June, marking the point when the Northern Hemisphere is tilted most towards the Sun, resulting in the shortest night of the year in that hemisphere.