A solar flare, a violent explosion in the Sun's atmosphere, is hurtling past the Earth at over one million kilometres per hour -- offering up a potentially brilliant light show while threatening to damage power grids and communications systems.

Star gazers in Canada and across the northern U.S. could be treated to a spectacular light show called an aurora, or Northern Lights, as early as Thursday night.

Images beamed from the Solar and Heliospheric Observatory (the SOHO space probe) showed a bright flash near the Sun's equator overnight. Several of SOHO's sensors became temporarily overwhelmed by the amount of radiation emitted by the flares.

Solar flares, known as coronal mass ejections, carry with them many protons and electrons which reach the Earth's magnetosphere, said McGill University physics Professor Robert Rutledge, "where it produces quite an auroral show which we should see tonight as far south as Boston and as far west as Victoria."

The danger

But these solar flares also send out clouds of charged particles that could damage communication systems and power grids.

Satellite operators and power grid managers have been advised to keep an eye on the solar storm over the next few days.

"There are actually very serious implications with possibilities for enormous current to take place in the atmosphere, which could then short up power stations," said Rutledge.

A solar storm on March 13, 1989 jolted Hydro Quebec and left six million people without power for up to nine hours.

Airliners on routes over the Arctic sometimes have to be diverted south, since the Earth's magnetic field offers less protection near the poles.

The storm is also a threat to satellites.

"If you bombard any electric equipment with protons and electrons travelling 1,000 kilometres a second, it can affect the computer systems and it could take some of them out," said Rutledge.

An important, unknown component to the storm is its magnetic orientation. If it lines up a certain way with the Earth's magnetic field, the storm could pour into the Earth's upper atmosphere and do some electrical damage. If it aligns otherwise it could simply pass by the planet with few consequences.

Astronauts alerted

NASA said the solar storm will not affect the current shuttle mission schedule.

Joe Kunches, lead forecaster at the NOAA Space Environment Center, told SPACE.com Thursday afternoon that astronauts aboard the International Space Station are not expected to be put at additional risk.

Still, the astronauts today were instructed to sleep in sections that are well-shielded from radiation.

Here on Earth, Rutledge said the magnetosphere and atmosphere do a good job absorbing much of the solar storm's blow. But he did warn Canadians to have some extra candles and blankets on hand -- just in case of a power outage.

What causes them

There's some mystery as to what exactly causes them, but Rutledge says they are related to the sun's magnetic field, which is tied to its core.

"As the sun rotates it can wind its magnetic field up very tightly -- producing a big, dense ball of magnetic energy. That ball rises to the surface, bursting through and breaking through the surface. That's what gives us the solar flare."

The biggest solar explosion ever recorded erupted from the Sun's surface on Nov. 4, 2003.

The blast sent billions of tons of superhot gas into space, some of it directed towards Earth, but it did no damage.