Lightning has long sparked the human imagination, leading to the creation of myths, legends and lore for thousands of years. While the theories and stories may fascinate, the truth behind lightning is often just as shocking.

But what is lightning, anyway?

University of Arizona climate science specialist Mike Crimmins says lightning is much like the shock someone generates after shuffling across a carpet and touching another person. But instead of shoes on the ground, imagine ice particles in the clouds.

"In really hot conditions like we see during the monsoon, thermals of warm air will rise very quickly, and if they rise to a point where there is moisture in the atmosphere, it will condense and form into a cloud," said Crimmins, a professor of environmental science in the College of Agriculture and Life Sciences. "In that cloud process, the rising air starts to mix in the atmosphere very quickly. If you have little ice particles in those clouds – like we do in all of our clouds in this latitude and higher – they rub against each other and cause electrostatic charge separation."

During the early stages of a storm cloud's growth, the atmosphere acts as an insulator between the positive and negative charges building within the cloud – as well as between the cloud and the ground. When the opposing charges are strong enough, the insulating capacity of the air is overcome, and a rapid discharge of electricity occurs in the form of lightning.

Can lightning strike twice?

While science can explain the facts behind lightning, there are often misunderstandings about one of nature's most powerful displays, even in the modern era. Take, for example, the old adage, "Lightning never strikes the same place twice."

That is not the case, Crimmins said. Not only do lightning protection features on buildings, such a lightning rods, attract multiple strikes, but each individual strike can actually carry multiple discharges of energy.

"We have wonderful, high-speed photography that shows multiple pulses of lightning in a single strike," Crimmins said. "Once a channel is made between the cloud and a ground point, it's like a wire is connected and you can see multiple discharges. And if you look all over (the University of Arizona) campus, there are little metal spikes on the buildings and those absolutely get struck many times."

So, is it the metal that attracts lightning, or is it tall objects?

While lightning is attracted to both metal and taller objects, the explanation is more complicated, Crimmins said. The electrical discharge is searching for the path of least resistance, which involves factors like air currents, aerosols in the atmosphere and changes in humidity that will govern where lightning strikes.

"If you put a metal spike up on a building, it will likely be the path of least resistance for the charges that connect between the cloud and the ground," Crimmins said. "But there could be other things going on in the atmosphere and on the surface so that the charge goes around the metal high point and strikes somewhere else."

Is it safe to shower or drive in a lightning storm?

When lightning does strike a home or other structure, there are usually built-in measures that allow the electrical energy to flow safely through wiring and into the ground in a process known as grounding. But does that mean homes are completely safe? For the most part, yes, Crimmins said, but there are some lightning risks during storms that many people take to heart. For instance, the generally accepted guidance is to avoid showering during a thunderstorm because lightning could pass through plumbing, and corded phones could carry some risk of carrying an electrical charge from a strike, but Crimmins said the risk is slight in both cases.

When it comes to driving during a storm, most vehicles are designed to conduct electricity away from the vehicle's occupants and into the ground, keeping drivers and passengers safe, Crimmins said.

Lightning without rain?

Lightning strikes often take place during rainfall. So, why is there sometimes lightning without rain? Crimmins referred to this phenomenon – all too familiar to Tucsonans – as dry lightning, which occurs when precipitation falling from clouds evaporates before reaching the ground, while lightning flashes unabated.

Lightning can also strike when there are no storm clouds directly overhead. According to Crimmins, the National Weather Service says it best: When thunder roars, go indoors.

"If you can hear thunder, you can be struck by lightning – and that is really important to know," Crimmins said. "Lightning can strike ahead of storms, which is blue-sky lightning, and can be 10 to 20 miles outside of storms and tends to be positive charges and have a lot of energy associated with them. If there is thunderstorm activity, it is safer to go indoors."

Hearing thunder is not only a strong indication that a storm is brewing, but the sound can also be used to measure the distance to the storm. Thunder is created by the instant connection of charges through a poor conductor like the atmosphere, which superheats the air and causes a shockwave. That shockwave travels about 1 mile every five seconds after a flash of lightning.