Northern lights a reminder of the sun's influence on Earth

A flare that erupted on the sun this week should bring a show of northern lights to many parts of the country this weekend. The beautiful auroras are a visual reminder that the sun showers our planet with more than just light and heat.

Our star, the sun, is a fundamental provider of energy to the Earth, shedding light, driving the weather and feeding green plants. Life could not exist here without it.

But the glowing ball we see crossing our skies every day is only the visible part of the sun. Other forms of radiation we don't see shoot off from the surface, along with a constant wind of charged particles that wash over the Earth and the other planets in the solar system. So in a sense, we live inside the sun. 

The sun is an unbelievably powerful nuclear furnace, with energy and hot gasses bubbling up from its interior, like boiling soup, that sometimes concentrate into sunspots. These can cluster together producing powerful loops of magnetic energy.

Occasionally these loops become strained and burst, releasing a bright flare of powerful X-rays, often accompanied by what's called a coronal mass ejection, an enormous blob of plasma — or superheated electrified atoms — that is shot out into space like a tornado out of a thunderstorm. 

When one of these eruptions is pointed at the Earth, as happened this week, we see the effects in space and on the ground. In March 1989 a super powerful blob struck the Earth's magnetic field. This generated electrical surges in power lines on the ground that shorted out the entire power grid of Quebec and parts of the northeastern US. Since then, electric utilities have hardened their systems to try to prevent similar blackouts in the future.

Satellites have been knocked out of service by electrical interference from solar storms. They've also been knocked out of orbit as the sun's activity inflates our atmosphere, causing drag that slows spacecraft down.

And speaking of the atmosphere, the ionosphere — the electrically charged upper layer of our atmosphere — can be disturbed by solar flares, interrupting some radio communication that uses that layer to bounce signals around the Earth. Astronauts aboard the International Space Station have been asked to temporarily move to the central core for protection against X-ray radiation during intense solar storms.

While solar storms can disrupt our technology, they pose no direct threat to us on the ground, thanks to the protection provided by the Earth's magnetic field. Particles from the sun do not reach the surface. Instead, they follow the magnetic field towards the north and south poles, where they interact with the atmosphere giving us the spectacular celestial light show of the Northern lights, or Aurora Borealis in the northern hemisphere and Aurora Australis in the south. 

Vast curtains of light, sometimes draping across the entire sky from horizon to horizon, glow in different colours depending on the way different gases in the atmosphere are set aglow at different altitudes. Green is most common, from oxygen, while nitrogen produces red. The lights seem to reach all the way to the ground but in fact, all the activity happens about 100 kilometres up. That means the lights are safe to watch.

Aurora are a permanent feature of the Earth as well as other planets with magnetic fields, such as Jupiter and Saturn. They form glowing rings around the poles like jewelled crowns. But when the sun gives off a burst of activity, the rings are pushed toward the equator, which in Canada, means more densely populated regions in the south can see them.

So if you have clear skies over the next few nights, find a dark place and look to the sky. If you do see the light show, think about the fact that you are looking at the effects of a storm that took place 150 million kilometres away on the roiling surface of our star.