Lightning is an atmospheric discharge of electricity, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms. A bolt of lightning can travel at a speed of 100000 mph (160934 km/h), and can reach temperatures approaching 28000 °C (60000 °F), hot enough to fuse soil or sand into glass channels. There are over 16 million lightning storms every year.

How lightning initially forms is still a matter of debate: Scientists have studied root causes ranging from atmospheric perturbations (wind, humidity, and atmospheric pressure), to the impact of solar wind and accumulation of charged solar particles. Ice inside a cloud is thought to be a key element in lightning development, and may cause a forcible separation of positive and negative charges within the cloud, thus assisting in the formation of lightning.