Lightning is a discharge of atmospheric electricity which is triggered by a buildup of differing charges within a cloud. The result is a sudden release of electricity which causes a distinctive bright flare, followed by a thunderclap. Lightning is most common around the equatorial regions of the world, although it can potentially strike anywhere, and it appears in a variety of guises, depending on atmospheric conditions.

There are several competing theories to explain why differing electrical charges appear in clouds, although scientists suspect that it may be related to the presence of ice crystals in the cloud. Typically, the bottom of a cloud become negatively charged, and it sends out what is known as a “leader” which seeks a positive charge, either in another cloud or on the earth. As the leader approaches an area which is positively charged, a positively charged streamer emerges, meeting the leader, sealing the connection, and generating a bolt of lightning.

After the lightning travels to the ground or another cloud, it may strike again several times within a fraction of a second. These re-strikes are so fast that people cannot register them with the naked eye; instead, they appear as a single strike. The lightning moves so quickly that it superheats the surrounding air, causing a sudden rapid expansion which creates a shockwave. Shockwaves are responsible for thunder; because thunder is so closely associated with lightning, some people attempt to judge the distance of a storm by counting the time which elapses between a lightning strike and a thunderclap.

Most lightning travels from cloud to cloud, or from a cloud to the ground. In rare circumstances, however, the charges will be reversed, and lightening will emanate from the ground. This is known as “positive lightning,” and it is rare and extremely dangerous. Positive lightning is often triggered by human activities, such as the liftoff of a rocket or the detonation of a nuclear device.

Many people associate classically jagged streaks in the sky with lightning, but lightning can also appear in bursts known as bead lightning, or it can reflect from the clouds, making sheet lightning. Some people may also be familiar with ball lightning, an unusual manifestation of lightning which is rarely observed.

If you are caught outside during a lightning storm and you cannot shelter in a car or house, you should hunch your body close together, making yourself a small target, with only your feet touching the ground. Indoors, stay away from phones and plumbing, as lightning can sometimes travel through phone wires or plumbing systems.