A huge energy zone 400,000 miles from Earth has been identified as the power source for the Northern and Southern Lights, which are like shimmering pictures on "Mother Nature's TV set," a physicist says.
Recent analysis of some of the 200,000 photographs of the lights taken by the Dynamics Explorer 1 satellite allowed researchers to calculate the location of the power supply for the first time, said University of Iowa physicist Lou Frank.
The invisible, egg-shaped zone of electrically charged particles is 20 to 30 times the size of Earth and is about 400,000 miles distant, always on the side of the Earth away from the sun, he said.
Magnetic forces in the zone trap particles from the solar wind, a hot, particle-laden gas that speeds from the sun at nearly 1 million m.p.h., Frank said.
'Series of Green Curtains'
From the ground, the Northern and Southern Lights--also called the aurora borealis and aurora australis--usually are visible from high latitudes as "a series of (60- to 70-mile-tall) green curtains marching and waving across the sky," although they also may appear as a reddish glow, Frank said.
The auroras occur because solar wind pushes the magnetic field around the Earth to create an electric voltage, or power supply, in the planet's magnetic "tail"--the 4-million-mile-long part of Earth's magnetic field blown away from the planet by solar wind, he said. Through complex reactions, the voltage accelerates the particles into Earth's polar regions, where they funnel into the atmosphere and are illuminated to create the lights.
"It's Mother Nature's TV set, and the top of Earth's atmosphere is the screen," said Frank, who presented his findings at the Jet Propulsion Laboratory near Pasadena during an international conference on solar wind interaction with Earth's magnetic field.
"There is a high voltage in a TV set, and this voltage accelerates particles into our TV screen" to create a picture, he said. "Mother Nature's power supply is thousands of miles above Earth's atmosphere. What she does rather than run old movies is she runs a display of Northern and Southern Lights."
The photos from Dynamics Explorer 1, launched from Vandenberg Air Force Base into a 15,500-mile-high polar orbit in 1981, are the most detailed yet of the auroras, Frank said. They do not actually show the power supply that creates the lights, but allowed researchers to locate their power source.