Aurora dance across the night sky on one of Gina’s dog sled trips in the White Mountains north of Fairbanks, Alaska.

The aurora are curtains of light emitted from the upper atmosphere at heights of 100 to about 400 km above the ground. The upper atmosphere is driven by processes which are quite different to the more familiar lower atmosphere.

Aurora light up the optics laboratory, part of the rocket range at Poker Flat, Alaska, 1992.

While there is virtually no water vapour, and hence convective clouds or thunderstorms, there are huge geomagnetic storms which are manifested in the visible aurora. Centred on the northern and southern polar regions, auroral substorms may deposit up to a million Megawatts of power producing large currents and stirring up the whole upper atmosphere.

An artist's "cartoon" showing the Earth’s magnetic field, or magnetosphere, which which forms a womb-like shape encasing the earth.

The source of auroral energy is the solar wind, a persistent stream of charged particles emitted by the sun, which is highly variable in strength. The charged particles are then guided and accelerated by the magnetic field of the earth, until they finally reach the atmosphere and light up. The dancing lights of the aurora are thus the footprint of powerful processes occurring in the earth's magnetosphere, in which the earth sits encased in a womb-like way.

Aurora fill the night sky, adding passion to the romantic tent lights, White Mountains, Alaska.

Auroral displays vary greatly, from faint quiet arcs reaching from horizon to horizon, to active displays of colour and movement, seen dancing and cartwheeling across the skies.

Known as the Aurora Borealis in the northern hemisphere and Aurora Australis in the southern hemisphere, mirror images of the aurora produce crowns of light encircling both poles. Thus the aurora is a global phenomenon which manifests simultaneously at both ends of the earth.