Geography Concepts — UPSC Prelims

Summer Solstice (June 21) — the longest day in the Northern Hemisphere; the sun is directly overhead at the Tropic of Cancer (23.5°N). Winter Solstice (December 21) — the shortest day in the Northern Hemisphere; the sun is directly over the Tropic of Capricorn (23.5°S).

Vernal Equinox (March 20-21) and Autumnal Equinox (September 22-23) — day and night are approximately equal across the globe; the sun is directly over the equator.

The axial tilt of Earth at 23.5° to the orbital plane is the fundamental cause of seasons. Without this tilt, there would be no seasonal variation in day length or solar intensity.