What causes the aurora?

What causes the aurora?

• A. Solar wind interacting with the Moon causes lights in the sky.
• B. Lightning in the upper atmosphere lights the sky at high latitudes.
• C. Charged solar particles interacting with Earth's magnetic field and atmosphere, emitting light in polar regions.
• D. Reflections of sunlight off ice crystals high in the atmosphere.

Answer: (C)

The aurora happens when charged particles from the Sun, carried by the solar wind, meet Earth’s magnetic field and atmosphere. The magnetosphere redirects many of these particles toward the polar regions along the magnetic field lines. There, they collide with atoms and molecules in the upper atmosphere, transferring energy. When those atoms and molecules return to their normal states, they release photons, which we see as glowing curtains or arcs of light near the poles. The colors depend on the altitude and the gas involved—green from oxygen at typical aurora heights, red from higher-altitude oxygen, and purples/blue from nitrogen. Lightning or reflections off ice crystals don’t drive the aurora, so those ideas don’t fit.

The aurora happens when charged particles from the Sun, carried by the solar wind, meet Earth’s magnetic field and atmosphere. The magnetosphere redirects many of these particles toward the polar regions along the magnetic field lines. There, they collide with atoms and molecules in the upper atmosphere, transferring energy. When those atoms and molecules return to their normal states, they release photons, which we see as glowing curtains or arcs of light near the poles. The colors depend on the altitude and the gas involved—green from oxygen at typical aurora heights, red from higher-altitude oxygen, and purples/blue from nitrogen.

Lightning or reflections off ice crystals don’t drive the aurora, so those ideas don’t fit.