Is Lightning Hotter than the Sun?


What's five times hotter than the sun and capable of sending a DeLorean back to the future?

Yep, the answer is a bolt of lightning, which can reach temperatures of roughly 30,000 kelvins (53,540 degrees Fahrenheit). The sun, on the other hand, is eclipsed in this case — its surface temperature is just 6,000 kelvins (10,340 degrees Fahrenheit). It's one amazing piece of science trivia, but what exactly does it all mean?

First, it's important to realize that the sun's surface is actually its coolest layer. Dive down to its core, and you'd encounter plasma temperatures of about 15 million kelvins (about 27 million degrees Fahrenheit). Things also heat up just above the sun's surface, as its atmosphere exceeds temperatures of 500,000 kelvins (about 900,000 degrees Fahrenheit).

"Power is the rate at which energy is used or transferred," explains University of Washington physics professor Robert H. Holzworth. "So power is energy per second, and the energy per second in lighting can be very high, but it only lasts a really, really, short time, like tens of microseconds. So the total energy isn't like the total energy from the sun, obviously, but the rate the energy dissipates can be very large. It's one of the most powerful natural phenomena on Earth."

But just where does all that energy come from?

"Ultimately that energy comes from the sun," Holzworth says. "The sun heats up the surface, which results in differential heating. One area is warmer than another, and warm air rises since it's less dense. When you have moisture in the air, that parcel of air can go up much higher than it would otherwise. That's the basis of very strong convection."

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At this point, Holzworth explains, ice forms in the parcel of rising air.

"You can get very efficient charge transfer, so that you get positive and negative charges separated by the bouncing ice," Holzworth says. "It turns out that when you have ice collisions, there's some likelihood that, at certain places in the cloud, smaller ice formations such as snowflakes are going to get charged positive, leaving behind negative charge on the hail stones or the soft hail."

The lighter, positively charged ice particles continue to rise toward the top of the clouds. Meanwhile, the heavier, negatively charged ice particles plummet, thus separating the charge in a process known as gravity separation.

This process creates a strong electric field, which in turn ionizes the air around the cloud, separating air molecules into positive ions and electrons. Electrons move far more easily in ionized air. Once a channel of ionized air is established from cloud to ground (or between two points in a cloud), high-temperature current flows in the form of a lightning stroke that neutralizes the charge separation.

Richard E. Orville, director of Texas A&M University's atmospheric sciences department, equates the breakdown of an electrical buildup to an incident he witnessed in eighth grade involving a screwdriver and an electrical socket.

"There was a fellow sitting in front of me, and for some reason he had a screwdriver in his hand," Orville said. "He stuck it in the wall socket and received a very big discharge. Of course that's because you had an excess of electricity in a plug just waiting to be tapped, which we do every day when we plug in a device. So in this case, you've got a buildup of electrical charge in the base of a cloud, and breakdown occurs when the electric field gets high enough."

So while it wouldn't be accurate to say a bolt of lightning is hotter than the sun itself, these flashes of electrical energy do reach higher temperatures than the surface of the sun.

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