Tom Hamlin, age 7, of Orlando, Fla., for his question:

WHAT CAUSES THUNDER?

The sound of thunder is caused by the violent expansion of air that has been heated by lightning. Ancient people thought it was caused by angry gods who were roaring their anger because they weren't happy with the people on earth.

When an electrical charge of lightning passes through the air, it is heated instantly. The heat causes 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 air wave which has the sound we know as thunder.

Thunder actually has a number of different sounds. The deep, roaring, rumbling type is caused by the air wave 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.'

The sound of thunder reaches us after we have seen the lightning because light travels faster than sound.

You can tell about how far away the storm is if you count the time between the flash of lightning and the sound of thunder. If it is five seconds between the two, the storm is about one mile away.