Gerald Heady, age 8, of Santa Rosa, Calif. for his question:
WHAT CAUSES LIGHTNING?
Lightning is a flash of light in the sky that is caused by electrical current. The current may flow between parts of the same cloud, between clouds and the earth or between different clouds.
When a solid body becomes electrically charged, only its surface has a charge. But when a thundercloud becomes charged, the whole cloud has a charge.
A thundercloud actually is made up of a tremendous number of tiny water droplets. Each droplet has a charge on its surface, thus a cloud may have a great electrical potential.
If a cloud comes near an opposite electric charge, a huge spark may result. When a charged cloud comes near the surface of the earth, an opposite charge is induced on the surface of the earth.
The air that separates the earth and the cloud actually acts as an insulator. It resists the effort of the opposite charges of electricity to rush together. But when the electrical potential becomes large enough, it overcomes the resistance of the air.
Then a lightning flash occurs. The flash is really a huge spark, similar to that produced in the spark plug of your family automobile.
Scientists ave found that one stroke of lightning can measure more than 15 million volts.
A spark between a cloud and the earth may measure as much as eight miles long. It may travel at the rate of 100 million feet per second.
Lightning that reaches between opposite charged clouds may have a length of 20 miles. Photographs of lightning obtained by radar indicate that some cloud to cloud lightning strokes may measure 100 miles long.
Lightning between clouds does not cause any damage on earth, because the electrical energy is dispersed in the air. Lightning between clouds and the earth can cause damage.
As lightning travels, it heats the air in its path. The sudden heating causes the air to expand violently. The cool air farther away is pressed into a smaller space. This process starts a great wave of air that results in thunder.
Zigzag or chain lightning is a chain of brilliant light that follows an irregular path. The single streak of lightning often breaks into several branches or forks.
Sheet lightning has no particular form. It is really light from a flash of chain lightning that takes place beyond the horizon.
Heat lightning, often seen on summer evenings, is the same as sheet lightning, but the flashes are fainter. Thunder usually doesn't accompany heat lightning because it occurs too far away for the thunder to be heard.