What is the phenomenon responsible for the northern lights (Aurora Borealis) and southern lights (Aurora Australis)?

Answer and explanation

Correct answer: B. Charged solar wind particles colliding with atoms and molecules in Earth's upper atmosphere

  1. Step 1: Solar wind plasma travels along interplanetary magnetic field lines and enters Earth's upper atmosphere through polar cusps in the magnetosphere.
  2. Step 2: Collisions of energetic electrons with atmospheric oxygen atoms emit green (557.7 nm) and red (630 nm) light, while interactions with nitrogen emit blue and violet hues.
Answer
Charged solar wind particles colliding with atoms and molecules in Earth's upper atmosphere
Why not the others: 'Refraction of equatorial sunlight off Arctic and Antarctic ice sheets' Polar ice reflects sunlight, but cannot produce dynamic colored atmospheric light emissions at night; 'Thermal ionizing discharge from lightning in thunderstorms' Lightning discharges occur in the troposphere (below 12 km), whereas auroras occur in the thermosphere (above 80 km); 'Radioactive decay of radon gas escaping from tectonic faults' Radon gas decay produces alpha particles in soil, which do not create high-altitude auroral ribbons.

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