GS Paper I 2024 · Q15
15 marks · 250 words Geophysical phenomena & changing features X-Ray · Core #43What are aurora australis and aurora borealis? How are these triggered?
Approach · directive: “what / how”
What it asks · Define the southern and northern lights and explain the chain from solar activity to glowing gases in Earth's upper atmosphere.
It asks 2 things — answer each
- Define aurora australis and aurora borealis: what they are, where and at what height they occur
- Explain how they are triggered: from solar activity through the magnetosphere to the glowing upper atmosphere, and why it matters
Open with · Aurora borealis and aurora australis are the northern and southern polar lights of the thermosphere; IIA cameras recorded one even over Hanle, Ladakh, on 10–11 May 2024.
Cover
- Definition: Latin 'dawn'; Aurora Borealis in the north, Aurora Australis in the south (NCERT), in the thermosphere.
- Where and how high: two ovals near the magnetic poles, typically 80–500 km up (NOAA); Scandinavia, Alaska, Canada; Antarctica, Tasmania, New Zealand.
- Colours: green and red from oxygen, blue and purple from nitrogen.
- Trigger chain: solar wind and coronal mass ejections; magnetosphere stores energy; electrons accelerated along field lines to the poles.
- Excitation: collisions with oxygen and nitrogen transfer energy, released as light like a neon lamp.
- Storms: ovals expand towards the equator; the May 2024 CME storm reached Hanle, Ladakh (IIA).
- Significance: space weather threatens satellites, GPS and grids; Aditya-L1 watches the Sun from L1, about 1.5 million km away.
Close with · Auroras are the Sun–Earth link made visible; Aditya-L1's watch from L1 turns a polar spectacle into early warning for India's satellites, navigation and power grids.
Add value (verified)
- NOAA: auroras typically form 80 to 500 km above Earth's surface.Aurora — Space Weather Prediction Center, NOAA (US Government) ↗“The aurora typically forms 80 to 500 km above Earth’s surface.”
- NOAA: Earth's magnetic field guides the electrons so that the aurora forms two ovals centred on the magnetic poles, which expand away from the poles in major storms.Aurora — Space Weather Prediction Center, NOAA (US Government) ↗“Earth’s magnetic field guides the electrons such that the aurora forms two ovals approximately centered at the magnetic poles. During major geomagnetic storms these ovals expand away from the poles”
- NOAA: accelerated electrons collide with oxygen and nitrogen in the upper atmosphere and the energy is released as light, like a neon light.Aurora — Space Weather Prediction Center, NOAA (US Government) ↗“This is similar to how a neon light works.”
- IIA recorded intense auroral activity at Hanle and Merak, Ladakh, on 10–11 May 2024, caused by geomagnetic storms from coronal mass ejections.Intense auroral activity seen at Hanle and Merak in Ladakh (11 May 2024) — Indian Institute of Astrophysics, DST ↗“Intense auroral activity was captured by cameras at our Indian Astronomical Observatory in Hanle and Merak in Ladakh on the night of 10-11 May, caused by intense geomagnetic storms arising from Coronal Mass Ejections from the Sun impacting the Earth.”
- ISRO: Aditya-L1 is India's first space-based mission to study the Sun, in a halo orbit around L1, about 1.5 million km from Earth.Aditya-L1 — Indian Space Research Organisation ↗“Aditya L1 shall be the first space based Indian mission to study the Sun. The spacecraft shall be placed in a halo orbit around the Lagrange point 1 (L1) of the Sun-Earth system, which is about 1.5 million km from the Earth.”
Question: UPSC's CS (Main) 2024, GS Paper I — paper ↗. Approach: Minimalist IAS, checked 16 Oct 2026 (how we verify) — UPSC publishes no model answers. ·
Model answer· 333words · Minimalist IAS
Aurora borealis (northern lights) and aurora australis (southern lights) are natural light displays in the thermosphere, seen mostly near the poles. On 10–11 May 2024, cameras of the Indian Institute of Astrophysics recorded one even over Hanle in Ladakh, a reminder that their trigger lies on the Sun.
What auroras are
- Definition: aurora is Latin for dawn; NCERT names the display Aurora Borealis in the Northern Hemisphere and Aurora Australis in the Southern.
- Location: two ovals roughly centred on the magnetic poles: over Scandinavia, Alaska and Canada in the north; over Antarctica, seen from Tasmania and New Zealand, in the south.
- Height: the aurora typically forms 80 to 500 km above the surface (NOAA), mostly within the thermosphere.
- Colours: arcs, curtains and rays; oxygen glows green and red, nitrogen blue and purple.
How they are triggered
- Solar wind and CMEs
- magnetosphere stores energy
- electrons race down field lines
- collisions with oxygen and nitrogen
- light
- Solar source: the Sun streams charged particles as the solar wind; coronal mass ejections hurl faster, denser bursts, most often near solar maximum.
- Magnetosphere: Earth's field deflects most of this plasma; when the solar wind's field points southward, the two connect and energy enters the magnetotail.
- Funnelling: electrons are accelerated along field lines into the polar regions, where the lines converge, which is why auroras are polar.
- Excitation: colliding electrons pass energy to oxygen and nitrogen; the excited atoms and molecules release it as light, much as a neon lamp works.
- Storms: major geomagnetic storms push the ovals away from the poles; the May 2024 storm, driven by coronal mass ejections, brought auroras to unusually low latitudes.
Why they matter
- Space weather: the same storms disturb satellites, GPS, radio links and power grids; India's Aditya-L1, its first space-based solar mission, watches the Sun from a halo orbit around L1, about 1.5 million km away.
Auroras are the Sun–Earth link made visible; Aditya-L1's watch from L1 turns a polar spectacle into early warning for India's satellites, navigation and power grids.
Prepared by Minimalist IAS to the answer standard of Shivam Singh (mentor, 7 years) · facts checked against official sources (how we verify) · updated 16 Oct 2026. UPSC publishes no model answers: compare your structure and coverage with this, then write your own.
