A lightning bolt is about five times hotter than the Sun's surface
The visible surface of the Sun, the photosphere, is about 5,500 °C (10,000 °F). That is cool by the Sun's own standards, since its core is around 15 million °C, but it is far hotter than anything we usually meet.
Yet on a stormy afternoon, something hotter can flash right overhead. Lightning can heat the air it passes through to about 27,800 °C, or 50,000 °F. The US National Weather Service puts that at about five times hotter than the surface of the Sun.
Lightning is a giant electric discharge, inside a cloud, between clouds, or between a cloud and the ground. An average bolt of negative lightning, the most common kind, carries a current of about 30,000 amperes. Driven through air, which normally conducts electricity poorly, that current turns a narrow path into glowing plasma, and the air in it heats almost instantly.
Hot, but only for a moment
The comparison is real but needs a footnote. The Sun's surface holds its temperature all the time, A lightning channel reaches its peak only for an instant, so it is hotter, but for a flicker. The current climbs to its peak in 1 to 10 millionths of a second, and a single stroke lasts around 60 to 70 millionths of a second.
That sudden heat is also the source of thunder. The air in and around the channel has no time to move aside gradually. It expands explosively, sending out a shock wave that reaches us as a sharp crack or a long, rolling rumble.
Light reaches you almost at once, and sound takes far longer, which gives a simple way to judge distance. Count the seconds between the flash and the thunder and divide by five, and you have the distance in miles. Thunder can be heard only about 10 miles from the strike.
What causes thunder?
Lightning heats the air in its path to around 27,800 °C, about five times the Sun's surface, and that air's sudden expansion is the thunder we hear.
