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Budgie in a thunderstorm

Thunder and Lightning

Electricity       Heat      Forks       Distance      Thunder lore







Sheet or fork...




Thunderstorms often occur at the end of hot, sticky summer days. At this time, warm moist air rises quickly and forms large cumulonimbus clouds. Inside these tall dark clouds, air currents create strong updraughts and water droplets and ice particles rub against each other. As they bang together like this, it causes a build-up of static electricity. Lighter, positive charges gather at the top of the cloud and heavier, negatively-charged pieces of ice and water accumulate at the base. The ground below is also positively charged. Electricity flows between the charges and the difference between them increases. When the differences get big enough, they are neutralised and electricity is released as a flash of lightning.

This can occur in two ways:

  • within the cloud (sheet lightning)
  • between the cloud and the ground (fork lightning)

sheet lightning

fork lightning

Heat... top of page


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.


Building strikeStrikes – 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 top of page

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:


Thunder eagle

  • 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.


Now that we've had a look at clouds and some of the weather features they create, we can move on to another form of moisture in the air for the next section.  This time it's mist and fog.
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