Now, this is the stupidest question I have ever herd. I studied greek mythology, and I also studied science. You see, greeks did not have the technology that we have to tell weather, or other stuff. Greeks believed that Zeus made lightning, when in reality Lightning is an electric current. Within a thundercloud way up in the sky, many small bits of ice (frozen raindrops) bump into each other as they move around in the air. All of those collisions create an electric charge. After a while, the whole cloud fills up with electrical charges, and lightning is formed.