Tanya, of Ngahere School, asks :-

What is lightning made of?

Pat Bodger, a high voltage electrical engineer at the University of Canterbury, responded.

Lightning is a form of electrical breakdown of air over extreme distances.

During thunderstorms, positively charged air molecules drift to the upper layers of a cloud while the bulk of the cloud becomes negatively charged. This charge separation sets up electric fields and hence voltages within the cloud, between neighbouring clouds, and between the cloud and earth.

Electrical breakdown of the air occurs initially as a local discharge. Once this has occurred then more follow, using the initial discharge channels. Inter-cloud discharges are the most common, but not always seen. For the cloud to earth breakdown, a leader of ionised air reaches down to earth as a progression of steps. Near the ground, the leader is met by a positively charged streamer which then proceeds back up to the cloud. This is known as the return stroke. Down and up strokes may occur a number of times but because they travel so fast we see only one heavy flash of light.

The light is the photons emitted when charged air molecules collide and combine. The charge movement or current of the strokes is so large, it heats up the air around the stroke channel very rapidly. The air expands as an explosion which we know as thunder.