I was driving in Nebraska on highway 80 going west near after grand island when i looked to the sky and noticed a big circular object moving at a high speed. It was bright green and glowing and was a little smaller than the size of the sun. I had no idea what it was when i first noticed it because it was too big to be anything identifiable. It seemed to be over 10000 ft high but no higher than 14000. I spotted it midway in the sky and it quickly sank below the horizon never to be seen again. I didnt even see it for more than 45 seconds. I was stunned when i saw it and immediatly thought it was a UFO. I was excited and scared and looked all around for other signs of UFo's. I considered calling the highway patrol but knew they would do nothing about it.