What 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 (northern lights) and aurora australis (southern lights) are natural light displays in high-latitude skies, produced when charged solar particles strike the upper atmosphere.
Cover
- Where: auroral ovals around the geomagnetic poles — Scandinavia, Alaska, Canada in the north; Antarctica, Tasmania, New Zealand in the south.
- Source: the Sun's solar wind and coronal mass ejections carry charged particles into space.
- Funnelling: Earth's magnetic field deflects most particles, but channels some along field lines towards the polar regions.
- Excitation: accelerated electrons collide with oxygen and nitrogen about 100–300 km up; atoms release light as they return to normal state.
- Colours: green and red from oxygen at different heights; blue and purple from nitrogen.
- Storms: strong geomagnetic storms push auroras to lower latitudes — the Hanle observatory in Ladakh recorded one in May 2024.
- Significance: a visible sign of space weather that can disrupt satellites, GPS and power grids; Aditya-L1 studies the solar wind.
Close with · Auroras are the visible signature of the Sun–Earth link — beautiful, but also a reminder that space weather must be monitored.
Question: UPSC's CS (Main) 2024, GS Paper I — paper ↗. Approach: Minimalist IAS, checked 30 Sept 2026 (how we verify) — UPSC publishes no model answers. ·
Model answer · 295 words (UPSC limit 250) · Minimalist IAS
Aurora borealis (northern lights) and aurora australis (southern lights) are natural light displays in high-latitude skies, produced when charged particles from the Sun strike gases in Earth's upper atmosphere.
What they are
- Location: oval belts around the geomagnetic poles — over Norway, Iceland, Alaska and Canada in the north; over Antarctica, seen from Tasmania and southern New Zealand, in the south; the two are near mirror images.
- Form and height: curtains, arcs and rays between roughly 100 and 300 km, in the thermosphere.
- Colours: green from oxygen at roughly 100–300 km, red from oxygen above that, blue and purple from nitrogen.
How they are triggered
- Solar source: the solar wind streams charged particles continuously; coronal mass ejections and coronal holes send faster, denser bursts, most often near the peak of the 11-year solar cycle.
- Magnetosphere: Earth's magnetic field deflects most of this plasma; when the interplanetary magnetic field turns southward it reconnects with Earth's field, letting energy and particles into the magnetotail.
- Funnelling: stored particles are accelerated back along field lines into the polar regions during substorms — the field lines converge at the poles, which is why auroras are polar.
- Excitation: electrons collide with oxygen atoms and nitrogen molecules, lifting them to higher energy states; as they relax they emit photons of specific colours.
- Storms: strong geomagnetic storms push the ovals to lower latitudes — the May 2024 storm was recorded even from the Hanle observatory in Ladakh.
Why they matter
- Auroras are the visible face of space weather, which can disrupt satellites, GPS, radio and power grids (Quebec blackout, 1989); India's Aditya-L1 mission (2023) monitors the solar wind from the L1 point.
Auroras are the visible signature of the Sun–Earth link — beautiful, but also a reminder that space weather must be monitored.
Written by Minimalist IAS from facts checked at source (how we verify) — a little fuller than exam length, so every part of the question is covered; in the hall, keep the structure and trim the detail. UPSC publishes no model answers: compare your structure and coverage with this, then write your own.