In less than a millisecond, up to a billion trillion electrons may reach the ground; the current may be as high as 200,000 amperes. We now see the main act of lightning, the return stroke. The return stroke, travelling at almost half the speed of light, is able to reach 3 or 4 miles back up to the cloud and relieve it of its large excess of negative charge--about 100 quintillion electrons. The channel that was established by the first big bolt can be used again and again. The cloud is not fully drained, and after a thirtieth of a second or so another bright lightning bolt may occur. This usually happens 3 or 4 times during the half- second that we call a "lightning flash."

On one occasion lightning used the same track 42 times. This accounts for the "flicker" of lightning that is often seen. No discussion of lightning is complete without talking about lightning`s integrated partner...thunder.