large umbrella shape of a Strob light emitting a light every 5-8 seconds apartWe were driving on I90 to spokane for christmas and in the distance there was a bright strobe that when flashed it lit up the entire sky. At first i thought it was a tower, but continued to travel West towards us. It was about the size of your thumb nail (the strobe) as it flashed, couldnt see any shape to any craft.Which flew over our heads. couldnt tell the speed of travel because I was traveling 75 mph on the freeway. There was no red or green aircraft lights like I normally see which I mentioned to my wife.