Last night's Nova Science Now << http://www.pbs.org/wgbh/nova/sciencenow/3214/02.html

...

presented a new interesting theory about how lighting is caused. Thunder clouds store relatively stable electrical charges on their top (positive) and the bottom (negative) sides. The cloud acts as an insulator. To generate lighting, something has to distabilize the system by building an electrical pathway from the top to the bottom of the cloud. One researcher was proposing that high-energy particles, like gamma rays from cosmic ray bursts may be the causative agent. The cosmic rays strike atoms in the top of the cloud sending a spray of electrons and other particles through the cloud. The electron stream creates the first conductive channel through the cloud. The stored charges on either side of the cloud tunnel through this initial channel, resulting in a cascading charge collapse that we see as lightning.

Cool, if it's right - dying stars triggering lightning on the Earth millions of years later. - Canopus56(Kurt) __________________________________ Yahoo! FareChase: Search multiple travel sites in one click. http://farechase.yahoo.com