Mapping the greatest light show on Earth

The aurora borealis can wreak havoc on communications systems. Picture / Reuters

They call it the greatest light show on Earth.

Usually confined to the polar latitudes, these swirls of dancing reds and purples briefly fill the night sky, and those who witness them can only wonder and gape.

For generations, they have fed myths and legends. Are these dazzling pulses of colour the celebrations of the gods, or songs of anguish from the spirits of departed men and animals?

Now the mystery of the northern lights, also known as the aurora borealis, so-named by the French astrologer Pierre Gassendi in 1621, is set to be unlocked, thanks to a gigantic international research effort now in its final phase of preparation.

Called Themis, it is being primarily sponsored by Nasa and the Canadian Space Agency, and involves astronomers and scientists from around the globe.

Collecting the data will be a fleet of five satellites to be launched by Nasa in October next year. They will fly in formation over northern Canada, monitoring and photographing the lights at the moment they occur from a vantage point in space.

At the same time 20 highly sophisticated digital cameras at remote locations all over Canada and Alaska will snap images of the sky once every five seconds.

For scientists like Dr Eric Donovan of Calgary University in Alberta, who is overseeing the placement of the ground-based cameras, the primary goal is to understand the energies involved in our magnetosphere that create the displays of light, known as auroral substorms or eruptions.

Scientists know solar winds cause the ionisation of gases in space, known as plasmas. But what interests them is what causes the electrical charges suddenly to create new energy - giving rise to the displays.

Dr Donovan likens it to the snapping of an elastic band in space. "We are looking at how energy is stored in one form and then is released violently and changes its form."

But there could be important spin-offs from the project, including discovering what triggers the much larger, and more rare, full-blown magnetic storms.

Then the borealis can suddenly streak thousands of kilometres southward - in North America as far as New Mexico - turning the pleasant light show into something more menacing.

The biggest storms - they can occur maybe 15 times a year - can wreak havoc on our communications systems, affecting everything from the navigation of aircraft to the proper operation of cash dispensers and the transmission of electricity.

Data-collecting is to continue for about five years.

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