Thunder and lightning are part of a thunderstorm.
When you hear thunder, there will be lightning.
Lightning is a giant spark of electricity.
Lightning happens in clouds
The air around the lightning makes the sound of thunder.
What causes thunder and lightning?
Thunderstorms form in cumulonimbus clouds. In this type of cloud there are drops of water, hailstones and specks of ice. As the water drops and the ice particles rub and bump against each other, they become charged with electricity.
There are positive charges (called protons) and negative charges (called electrons) in electricity and during the storm these charges separate. The positive charges form at the top of the cloud and negative charges form at the bottom of the cloud.
Positive and negative charges are attracted to each other and as they travel through the air the electric current causes a spark, which is lightning. So lightning happens inside a cloud and between clouds.
As the storm builds the negative electrical charge at the bottom of a cloud creates a positive charge in the ground below. As the negative charge get stronger, the air cannot stop it from jumping from the cloud towards the positive charge on the ground. The giant spark of electricity is the lightning that we see.
As the lightning heats the air around it, the air expands outwards at great speed, and there is a hole left in the air, called a channel. When the lightning is gone, the air collapses back in, creating the sound that we hear as thunder.
Lightning is dangerous
The temperature of lightning can be six times hotter than the temperature on the surface of the sun. Lightning is very dangerous and will strike anything that stands high above the ground; mountains, people, and buildings. Trees are often struck by lightning causing them to fall, or catch fire. Every year hundreds of people are killed by lightning but even so, the chances of being struck by lightning are very low.
Safety during a thunderstorm
During a thunderstorm, the safest place to be is indoors or in a hardtop car with the window up. Inside the house, stay away from windows, don't use the telephone unless it is a cordless phone, and turn off computers and other electrical appliances. Keep away from water too.
If you are caught outdoors, don't open an umbrella and avoid standing in open spaces. Keep away from a tree that is standing on its own; this is not a safe place to shelter. You will be safer if you find shelter in a clump of shrubs or in a group of small trees on low ground. Stay away from all water, even just puddles, as it can be dangerous during an electrical storm. Wait for 30 minutes after the last lightning before leaving your shelter.
How far away is the thunderstorm?
Thunder travels 1.6 km (1 mile) in 5 seconds. To work out how far away a thunderstorm is, count the number of seconds between when you see a lightning flash and when you hear the thunder. For every count of three, the storm is about one kilometre away.
Thunder and lightning happen at the same time, but the light travels faster than sound, so the lightning flash reaches your eyes before the sound reaches your ears.
Benjamin Franklin proved that lightning is electricity
Until about 300 years ago, people thought that lightning was a mysterious force that was a punishment from God. Inventor Benjamin Franklin (1706-1790) set out to prove that lightning was a form of electricity.
This is the story that is often told!
In 1752, Benjamin Franklin, using a kite and a metal key, proved that electricity was in the sky. He stood in a thunderstorm! Electricity from the storm clouds flowed down the wet string and when Benjamin touched the key, he received an electrical shock.