Thunder and Lightning

This can occur in two ways:

As the lightning strikes, it heats the air around it. Lightning bolts can heat the air to as much as five times as hot as the surface of the sun – approximately 30,000 °C (54,000 °F). This heat causes the air around to expand explosively, resulting in the loud crash called thunder.

Although the two happen together, you always see a flash of lightning before you hear the crash of thunder. Do you know why this happens? It is because light travels faster than sound.

Strikes – lightning always takes the quickest path to the ground and usually strikes tall isolated objects such as trees or tall buildings. This is why it is dangerous to shelter under trees during a storm.

Lightning fact: the Empire State building is struck by lightning approximately 8 times each year!

Forks

Each fork of lightning is actually two strikes travelling quickly up and down the same path. The first bolt (the "leader stroke") zig-zags downwards and completes the circuit between cloud and ground. This is followed a split second later by a huge surge (the "return stroke") that shoots back up the path just created.

How close is it?

You can work out approximately how far away a storm is by counting the number of seconds between seeing a flash of lightning and hearing the thunderclap. Because light travels faster than sound, the sound of the thunder will take about 2 seconds to travel 1 km. Therefore for every 2 seconds you count, the storm is 1 km away. If it is close, the thunder will sound like a loud crack, whereas if it is further away, it will sound more like a low rumble.

Thunder lore

Thunder has always been an awe-inspiring fact of nature, although it hasn’t always been as well understood as it is today:

• American Indians believed that thunder and lightning was caused by the sacred thunderbird. The thunder resulted from the flapping of its wings and the lightning flashed from its beak.
  

• The Norse god of thunder is known as Thor. He is always drawn in pictures wielding a heavy hammer. This hammer represents the "thunderbolt" that was once thought to fall from the clouds.

Make thunder. You can actually make thunder yourselves. To do this, blow up a small paper bag and then pop it. What happens? It makes a loud bang because the air inside has expanded quickly, just as it does when it is heated by lightning.