Bill Jason, age 10, of Nogales, Arizona, for his question:

WHAT CAUSES THUNDER?

Thunder is the sound caused by the violent expansion of air that has been heated by lightning. It isn't, as primitive man believed, the sound of angry gods who were displeased with the people on earth.

Air is heated instantly when an electrical charge of lightning passes through it. The heat cuases the molecules of air to expand, or fly out, in all directions. As the molecules seek more room, they collide violently with layers of cool air, and set up a great wave which has the sound of thunder.

Thunder has many different sounds. The deep, rumbling roar of thunder is caused by the air waves set up by the part of the lightning trunk that is farthest away.

The sharp crackle of thunder is set up when the large trunk of lightning forks out into many branches. And the loud crash of thunder is caused by the main trunk of the lightning.     '  she sound of thunder reaches us after we have seen the lightning. That is because light travels at 186,282 miles per second while Sound travels at a rate of only about 1,100 feet per second.