Myths associated with lightning and thunder are too many to count. The American Indians believed that lightning and thunder were caused by a mythical creature, the 'Thunderbird' by its beak and wings. Similarly, the Norse mythology attributes lightning and thunder to Thor―the Norse God of thunder, who used his hammer to cause them. Mythology aside, today modern science has the explanation to these natural occurrences ... and believe us, it's neither Thor, nor the Thunderbird. What Causes Lightning and Thunder? Lightning is the abrupt electric discharge, accompanied by the emission of light, which originates in the clouds during thunderstorms, dust storms, and volcanic eruptions. When it occurs, it is often accompanied by thunder, i.e., the loud sound caused by expansion of air. There are different types of lightning, such as the fork lightning, which occurs between the clouds and ground, and sheet lightning, which occurs within the clouds. Causes of Lightning Storms Basically, thunderstorms occur in cumulonimbus clouds which contain drops of water, ice particles, and hailstones. As these components of a cumulonimbus cloud rub against each other, they get charged. Generally, positively charged and negatively charged particles exist in sky at any given point of time. The difference, however, is that, they are evenly spaced in calm sky and unevenly spaced in thunderclouds. In these clouds, the particles which are positively charged are lighter and thus, they move upwards and form the upper portion of the cloud. On the other hand, those which are negatively charged are heavier, so they settle and form the base of the cloud. Going by the basic rule of opposites attract, these particles with opposite charge get attracted towards each other in course of time. While they travel towards each other, the electric buildup between them causes lightning to strike in the form of spark, which lasts for a second or two. In case of fork lightning, the negatively charged particles at the base of the cloud get attracted towards the positively charge particles on the ground. In case of sheet lightning, on the other hand, the negatively charged particles at the base of the cloud get attracted towards the positively charged particles within the same cloud (inter-cloud lightning) or in some other cloud in the surroundings (intra-cloud lightning). While the buildup of electric charge causes lightning (i.e., the flash), thunder is caused by lightning in turn. Causes of Thunder When you fill air in a balloon, it expands, and this expansion of air eventually makes the balloon burst with a loud bang. Thunder is caused by the same phenomenon, wherein lightning heats up the air and makes it expand, and expansion of air produces the loud noise which we call thunder. A single spark of lightning, which doesn't last for more than a second or two, has a temperature of around 54,000°F. This is way hotter than the surface temperature of the Sun. When the lightning strikes, it heats the air in the surrounding. This extreme heating of air results in its expansion, which, in turn, triggers thunder in the form of sound wave. You must have noticed that you first see lightning in the sky and then hear the thunder. This makes many people believe that thunder follows lightning. The fact, however, is that both occur simultaneously. It appears as if lightning precedes thunder, as light travels faster than sound. One of the frequently occurring natural disasters, lightning causes more than a hundred deaths every year in the United States alone―that explains why people are so scared of it.