“The upward branching in this photo shows that the Eiffel Tower actually initiated the discharge,” says lightning researcher Richard Blakeslee of the NASA Marshall Space Flight Center. “In other words, instead of starting in the cloud and coming to ground, this flash started when the tower ‘launched’ a leader that propagated upward toward the cloud (which still served as the source of the electric field needed to get the process going). As the leader ascended, it branched out. Eventually one of the branches reached a region of sufficient charge to ‘short out the cloud’ and produce the return stroke pictured above.”