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General Studies 2024 GS Paper I 15 marks 250 words Compulsory Explain

GS Paper I — Q15

What are aurora australis and aurora borealis? How are these triggered? (Answer in 250 words) 15

हिंदी में प्रश्न पढ़ें

ऑरोरा ऑस्ट्रेलिस और ऑरोरा बोरियालिस क्या हैं? ये कैसे उत्प्रेरित होते हैं? (उत्तर 250 शब्दों में दीजिए)

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Model answer

Written by UPSC Answer Check against this question's marking rubric, to the 250-word length. UPSC does not publish answers for Mains — this is one way to score well, not an official key.

Aurora borealis (northern lights) and aurora australis (southern lights) are natural light displays in the polar upper atmosphere, mainly in the thermosphere/ionosphere at about 100–400 km. They occur when charged particles from the Sun enter Earth’s magnetosphere and collide with atmospheric gases.

The trigger begins with solar activity. The Sun emits a solar wind of electrons and protons, usually in the eV–keV range, and during coronal mass ejections or high-speed streams it can send denser plasma that may be further accelerated toward Earth. When this plasma reaches Earth, it interacts with the magnetosphere. Magnetic field lines channel the particles toward the polar regions, where they precipitate into the atmosphere along the auroral oval, roughly at 65–75° latitude, rather than only at the cusps.

In the thermosphere/ionosphere, these particles excite oxygen and nitrogen molecules. Oxygen emits green light at lower auroral altitudes and red at higher altitudes; nitrogen gives blue and purple hues. The emitted photons create the curtains, arcs and rays seen as aurora.

Auroral intensity is linked to geomagnetic storms, measured by the Kp index, and to the 11-year solar cycle. The extreme G5 storm of May 2024 made aurora visible far south, including Hanle, Ladakh. India’s Hanle Dark Sky Sanctuary and the Indian Astronomical Observatory provide ideal sites for observing such events, while ISRO’s Aditya-L1 mission studies the solar drivers behind them. Thus, auroras are visible signatures of Sun–Earth coupling.

What "Explain" is asking you to do

Make the working of something clear — what sets it off, what follows from what, and what it produces. Explain is the Commission's mechanism word: it dominates the technical papers and the “explain why” stems, where the marks sit in the causal chain and not in the label.

Structure that answers it

State what it is → the initiating condition → the chain of cause, step by step → an instance where it plays out → what the chain produces

Where marks are lost

Describing what something looks like instead of why it works that way. Naming the stages without linking them reads as description too.

All UPSC directive words, compared →

How this answer will be evaluated

Approach

Framework: Geography: explain the mechanism, then location follows. explain: definition/context > points in order > small example > short close Full marks: Clear definitions, precise mechanism (solar wind -> magnetosphere -> excitation), and correct location.

Key points expected

  • Define aurora australis (Southern Hemisphere) and aurora borealis (Northern Hemisphere)
  • Identify solar wind and magnetosphere interaction as the primary trigger
  • Explain the role of charged particles (electrons/protons) in the process
  • Describe the excitation of atmospheric gases (oxygen/nitrogen) causing light emission

Evaluation rubric

Each sub-part is marked on its own, against the marks and word limit printed on the paper.

  1. The answer Define the two phenomena and explain the physical mechanism of their formation. 15 marks · 250 words

    explain— definition/context → points in order → small example → short close

    Must cover

    • Define aurora australis (Southern Hemisphere) and aurora borealis (Northern Hemisphere)
    • Identify solar wind and magnetosphere interaction as the primary trigger
    • Explain the role of charged particles (electrons/protons) in the process
    • Describe the excitation of atmospheric gases (oxygen/nitrogen) causing light emission

    Loses marks

    • Narrating a story of the sun without explaining the physical mechanism
    • Confusing the two auroras or failing to distinguish hemispheres
    • Focusing on mythology or cultural significance instead of the science

    Earns more

    • Mention specific colors (green/red) linked to specific gases (oxygen/nitrogen)
    • Reference the 'auroral oval' or specific latitude zones (60-75 degrees)
    • Mention the role of the solar cycle (11-year) in intensity
    • Distinguish between the two based on hemisphere and magnetic pole

    Extra mark

    • 30-second sketch map showing solar wind hitting the magnetosphere
    • One robust statistic on solar wind speed or particle density

Practice this exact question

Write your answer and it is marked point by point against the model answer above — what you covered, what you missed, what you got wrong.

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