Several people called the KPIX 5 newsroom after Sunday morning's magnitude 6.0 earthquake in Napa, reporting mysterious flashes of light in the sky. Witnesses said the strange phenomenon looked like lightning.
Similar flashes of light have been reported in earthquakes around the world, from Japan to Peru.
Friedemann Freund, a scientist with the SETI Institute in Mountain View, said the same thing happened during Sunday morning's earthquake. And it wasn't a transformer blowing up or UFOs.
"What they are, are a consequence of the stresses building up deep below the earth, seven miles like in the case of the Napa Valley earthquake," Freund told KPIX 5.
He calls the phenomenon "earthquake lights," the quick buildup of stress that causes an electric current to flow to the surface and burst through the earth. This typically happens before or during an earthquake.