I was driving nw from bethalto il entertaining alton il on il140 next to the alton mental health center. there was not much traffic, but i was in a small bunch of cars, 2 in left lane, 2 in right lane which i was 2nd car in left lane. i was just randomly gazing nw in the sky admiring its beauty and randomly saw this sea green colored oval light seemingly surrounded with a white/yellowish glow. it dropped strait down and seemed to cover 1/4 the sky in its decent. then from my vantage point, it seemed to stop and pull away from me (heading nw) and literally disappeared. it all happened so fast but i can replay it in my head over and over just like it was the first time i saw it. the two cars to my right pulled over and i just kept driving since my house was less than 2 miles away. just telling my wife the story as i pulled out my phone to call her, i was shaking uncontrollably. i have never seen anything like this, ever, and i have seen shooting stars and meteor showers. there were no light trails behind it, like if you were to see a shooting star. also, it was oval shaped but seemingly was sideways as the long parts were up and down as opposed to left and right.