Do Cosmic Rays Spark Lightning? – Instant Egghead #12

Ben Franklin began to study lightning
260 years ago but to this day scientists
still don’t fully understand how it forms. Sure, the basics are known. It’s like a zap of static electricity,
except on a much, much larger scale. In stormy updrafts, raindrops and ice particles rub together. Some become positive,
and others become negative. Then they’re pushed apart
by wind within the storm cloud As a result, the cloud ends up with areas of different charge. Lightning is the spark that jumps
between these areas. These sparks can also fly between the negative areas of the storm cloud, and the positive areas on the ground, say, through a tree, or a golf club. Simple, right? But there is a problem. The electric fields measured
in the thunderstorm clouds typically aren’t big enough
to trigger a spark. So what sets it off? Maybe, cosmic rays. The idea goes like this: cosmic rays, which constantly
bombard the earth, produce fast-moving,
highly energetic electrons. These electrons collide
with air molecules, which produce
more speeding electrons, and so on. This process is called Ronaway breakdown, and leads to an avalanche
of energetic electrons through the air. These electrons forge a conductive path in the air which triggers the discharge of lightning. Of course, the theory hasn’t been proved, and there are other ideas for spark mechanisms as well. It’ll take more work
to fully solve the puzzle of how lightning forms. In any case, remember,
the next time you get zapped pulling on a wool sweater, it just means you momentarily caught
a little bolt of lightning. For Scientific American’s
Instant Egghead, I’m Phillip Yam.