Sun’s path: Understanding Solstices & Equinoxes

Info Nuggets

Ravneet Kaur

Tribune News Service

Chandigarh, Updated At : 05:22 PM Sep 22, 2025 IST

Equinox and Solstice

1. Basic concepts

Earth’s tilt and revolution

• Earth’s axis is tilted at 23.5 degrees relative to its orbital plane (the ecliptic).

• This tilt + revolution around the Sun causes seasons.

2. Equinox

• From Latin aequus (equal) + nox (night).

• Occurs twice a year when the Sun is directly over the Equator.

• Day and night are nearly equal across the globe.

Dates:

• Spring (Vernal) Equinox: Rs March 21 (Northern Hemisphere).

• Autumnal (Fall) Equinox: Rs September 22-23 (Northern Hemisphere).

Features:

• Sun rises exactly in the east and sets exactly in the west.

• Length of day ≈ length of night (12 hrs).

• Marks change of seasons:

Vernal equinox → Spring begins in Northern Hemisphere, Autumn in Southern.

Autumn equinox → Autumn begins in Northern Hemisphere, Spring in Southern.

3. Solstice

• From Latin sol (sun) + stitium (stopped).

• Occurs when the Sun is farthest north or south of the Equator.

• Marks the longest and shortest days.

Dates:

• Summer Solstice: Rs June 21 (NH has longest day, SH has shortest).

• Winter Solstice: Rs December 21-22 (NH has shortest day, SH has longest).

Features:

• Sun is overhead at Tropic of Cancer (June solstice) or Tropic of Capricorn (December solstice).

• Extreme difference in day and night length.

4. Today’s context – Autumn Equinox (Sept 22, 2025)

• On this day, the Sun is directly overhead at the Equator.

• Marks the beginning of Autumn in the Northern Hemisphere (India included).

• Southern Hemisphere enters Spring.

• Day and night are roughly equal everywhere.

• After today:

Northern Hemisphere → days grow shorter, nights longer (winter approaching).

Southern Hemisphere → days grow longer (summer approaching).

5. Geographical & astronomical significance

• Equinoxes and solstices divide the solar year into four parts.

• Used in agriculture (sowing/harvesting seasons).

• Basis for many calendars and festivals worldwide.

• Equinox is important for celestial navigation.

6. Cultural & historical significance

• Many civilisations tracked equinoxes and solstices to frame calendars.

• Stonehenge (UK) and Maya temples (Chichen Itza, Mexico) align with these solar events.

• In India, harvest festivals and rituals often align with seasonal changes.

7. UPSC relevance

• Frequently asked under geography (world & Indian physical geography).

• Linked to: Latitude & seasons, tropics and Equator significance, time and calendar systems

• Possible framing in Prelims:

“On equinox, the Sun is directly overhead at…?” (Answer: Equator).

“Longest day in Northern Hemisphere occurs on…?” (Answer: 21 June).

Mains: Seasonality, agriculture, cultural geography, environment.

Summary for UPSC:

• Equinox → Equal day & night, Sun overhead at Equator (March & Sept).

• Solstice → Longest/shortest day, Sun overhead at Tropics (June & Dec).

• Today (Sept 22, 2025) → Autumn Equinox → marks start of Autumn in NH, Spring in SH.

Sun’s path: Understanding Solstices & Equinoxes

Ravneet Kaur

Tribune News Service

Equinox and Solstice

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