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Friday, 27 October, 2000, 01:00 GMT 02:00 UK
Spacecraft films spectacular light show
By BBC News Online science editor Dr David Whitehouse
Previously unseen aspects of a light show in the sky known as an aurora have been filmed from space.
The pictures were taken by the far-ultraviolet camera onboard Nasa's Image spacecraft. The movie shows a polar band of light brighten and fade over a two-hour period.
It depicts for the first time the global ebb and flow of hot, electrified gas (plasma) around the Earth as it is wafted by the solar wind.
The new images of the aurora were captured during a violent magnetic storm in the Earth's upper atmosphere in July.
Lights, camera, action
The aurora was formed when particles from the Sun hit the magnetic field that surrounds our planet - the magnetosphere - and produced a halo of light for four hours.
The glow was captured by the spacecraft Image as it travelled around the Earth on a voyage to study the vast but invisible field.
Launched in March 2000, the spacecraft follows a highly elliptical orbit which takes it so far from the Earth that, at times, the whole planet, and the aurora, can be seen within the field-of-view of the craft's camera.
Scientists say that such views will help them understand the basic physics of the outer atmosphere.
"A significant gap in our understanding of auroras has come from our inability to image proton auroras, which make up a large part of the aurora, because they are very diffuse and are almost invisible to the naked eye," said Stephen Mende, lead investigator of the far-ultraviolet instrument.
"Now they are visible in the far-ultraviolet region of the spectrum and, for the first time, we are tracking them to learn more about the structure of auroras."