Bright opal colored flash in the sky oround Iowa City, Iowa on Dec. 20th 2008.My wife and I were driving from Minnesota to Georgia via Iowa and were on the interstate (forgot the road number) heading south when the sky lit up totally green for about 2 seconds. Kinda like a lightning strike except it filled the whole sky, then it happened again about 5 seconds later. a bright opal colored flash covering the whole sky for about 1-2 seconds. We would like to know what that was and being there were many motorists on that highway at the same time, was wondering if anybody else had reported it and/or what they thought it was. I don't have a clue and it was just weird.