Looking South out my window around 10:20 PM. A golf ball sized glowing red-orange ball of light flew almost directly overhead from North to South. There was a jet taking off from SeaTac and I could make an easy comparison to it...This object had no blinking lights, but seamed to slowly pulsate. It moved very slow across the sky about a third of the speed of the jet, until fading out in the southern sky. I have seen many types of aircraft from SeaTac and Boeing Airfields and different helicopters including news, police and Harborview's medic copter, but this was unlike anything I have ever seen in the air. The only possible thing I could think of was it could have been a Japanese lantern, but I have never seen one of those in person either, so I can't say for sure. It was just strange. Also, I have been seeing a lot of strange lights over the Seattle area since about February.