Question: What causes lightning?

James Coombs OBrien answered on 16 Mar 2015:

First off you need a cloud that is full of water. When the cloud gets cold enough the water inside it freezes so you have a lot of small bits of ice inside. These bits of ice rub against each other which builds up electric charge.
You can do something similar if you are wearing socks by rubbing your feet on a carpet. This will build up an electric charge on you so if you touch something metallic you’ll get a very small electric (static) shock.

So the ice in the clouds build up a positive charge at the top of the cloud and a negative charge at the bottom. When this gets too much the positive and negative charges come together with a massive flash and a loud bang! This often happens inside the cloud.
Sometime the negative charge on the bottom of the cloud will hit a positive charge on earth instead of in the sky and lighting will hit the ground!

Thanks!