What are the northern lights?
What would the North Pole tourist bureau do without the northern lights? Ten-month winters don’t make for good travel brochures. But here, in this most inhospitable open-air theatre, you can witness the most hauntingly beautiful light show ever conceived in its full glory. Curtains of shimmering, chameleon-hued light as unpredictable as an artist’s temper.
The scientific explanation behind the aurora borealis (‘northern dawn’ in Latin) is almost as improbable and magical as the lights themselves. The Earth, it turns out, is constantly bombarded by highly charged particles blown around by solar winds. Few of these particles ever reach the atmosphere because they are deflected by the Earth’s magnetic field.
But every so often, the gentle solar winds turn into geomagnetic storms. Solar flares and coronal mass ejections (CME) – explosions of solar material into interplanetary space – can send powerful waves of charged particles toward the Earth. As these cosmic electrons collide with the Earth’s magnetic field, they generate millions of amps of electric current that arc along the magnetic field toward the poles.
If the force of a geomagnetic storm is severe enough, particles will breach the magnetic field at the poles, creating what is essentially the world’s biggest neon sign. As the supercharged electrons pass through the atmosphere, they excite gas atoms like oxygen and nitrogen.
The excited gasses emit different coloured lights depending on their altitude and the power of the surge. Low-altitude oxygen is responsible for the fluorescent green hues and high-altitude oxygen produces those brilliant crimson reds. Nitrogen flares up as shades of blue and purple.
The celestial light show is visible at the South Pole as well (there, it’s called the aurora australis), but the Antarctica tourist board is woefully understaffed.
Image © NASA
The cold vacuum of space seems an unlikely place for a storm. But that’s exactly what happens when a solar flare explodes into the Sun’s upper atmosphere, instantly heating nearby gasses to millions of degrees.
The extreme heat causes gas atoms to split into positively charged ions and negatively charged free electrons. This supercharged soup of ionised gas is called plasma. The Sun emits a constant stream of plasma in all directions at a speed of 500km/s (a million mph). But when the flow of plasma becomes a flood, the Earth is in for some bad space weather.
Geomagnetic storms cause more than the majestic northern lights. They can warp the Earth’s magnetic field so badly that satellites are knocked out of orbit and invading electrons overwhelm power grids. In 1989, 6 million people in Montreal, Quebec lost power for nine hours thanks to a particularly strong solar storm.
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