mock reading comprehension 4.3
We can sum up some of the things that we have learned as a result of the years of scientific detective work:
Auroras occur around Earth's north and south geomagnetic poles in regions known as auroral ovals. Southern auroras are called aurora australis; northern ones, aurora borealis.
The aurora is higher in the atmosphere than the highest jet plane flies. The lowest fringes are at least 40 miles above the Earth, while the uppermost reaches of the aurora extend 600 miles above the Earth. The space shuttle flies near 190 miles altitude.
Although there are stories about the aurora seeming to reach down into the clouds or to the tops of mountains, these are either illusions or some phenomenon other than the aurora. Only astronauts can fly through the aurora!
Some people believe that the aurora makes sound that accompanies the ripples and flow of the light. If the aurora does make sound, the sound would have to be generated here on Earth by some electromagnetic effect. Any noise generated by the aurora would take a long, long time to travel all the way to Earth, and the air up by the aurora is much too thin to carry sound. So does the aurora make noises? Nobody knows for sure!
Auroras occur because Earth's magnetic field interacts with the solar wind, a tenuous mix of charged particles blowing away from the sun. This wind from the sun sweeps by Earth in the interplanetary magnetic field which is produced by the sun. We are protected from the solar wind's direct effects by Earth's comet-shaped magnetosphere, where the Earth's magnetic field is distorted by the interplanetary magnetic field and the solar wind. The electrical energy generated by the charged particles blowing across the Earth's magnetic field send charged particles down into the Earth's upper atmosphere.
Auroral light is similar to light from color television. In the picture tube, a beam of electrons controlled by electric and magnetic fields strikes the screen