2024 · GS Paper 1 · Q15 · 15 marks
What are aurora australis and aurora borealis? How are these triggered?
In short
Aurora borealis and aurora australis are the northern and southern polar lights, glowing in ovals around the geomagnetic poles about 100-300 km up. They are triggered when solar wind and coronal mass ejections reconnect with Earth's magnetosphere and drive charged particles into oxygen and nitrogen.
Model answer
Ghissu Editorial · Verified 4 Oct 2026 · 279 words
Hemispheric twins
The aurora borealis glows over the Arctic and the aurora australis over Antarctica, often simultaneously as near mirror images.
Auroral ovals
They ring the geomagnetic poles near 65-70° magnetic latitude, over Norway, Alaska, Canada and Antarctica.
Height and colour
The glow forms about 100-300 km up; oxygen gives green and red, nitrogen blue and purple.
Solar source
The solar wind, boosted by flares and coronal mass ejections (CMEs), carries electrons and protons towards Earth.
Magnetic gateway
When the CME's field opposes Earth's, the two reconnect, and energy stored in the magnetotail drives particles down field lines to the poles.
Excitation
Colliding particles excite oxygen and nitrogen, which emit light as they relax, brightest near solar maximum, as in Solar Cycle 25.
Early warning
Aditya-L1, at the L1 point since 2024, can give advance notice of Earth-bound CMEs.
Protect infrastructure
The 1989 Quebec blackout and the loss of about 38 Starlink satellites in 2022 show why grids and satellites need storm protocols.
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Question from the official UPSC Civil Services (Main) Examination 2024 paper. Answer written by Ghissu's engine and checked against our editorial standards. Found an error? Tell us and we correct it within 48 hours.