I was driving. observed green oval traveling straight path, it was impossble to not notice this as it was large, green and bright. visible for 4-5 seconds moving much faster than a plane (5x or more a plane at cruise) then blinked out in an instant. this oval came from the north traveling right over niagara falls intl airport and niagara falls airforce base towards the south. i was on williams road, it was parallel. i observed it when it was next to me 90 degrees at about 33 degrees off the ground, green oval. had the apparent size of a full moon. other passenger in the car exclaimed loudly as did i. this wasn't something you'd not notice. no sound. it did not look like a meteor breaking up.No tail. no bright flashes. nothing breaking off it. it was a green perfect cicularly shaped object for the entire time we saw it.. 4-5 seconds. when it looked to be over grand island ny it blnked out. i mean it was there and then it was not there. it did not go behind clouds or below horizon. it simply blinked out. we were both amazed as this was stark, unambiguous. we have no clue what this was. i am 61 years old and i have seen many meteors, shooting stars break up in person and this was not that. i have never observed anything remotely like this. it moved in a straight line, consistent speed and altitude while we observed it. it made no manuevers or displayed any intelligent control. the way it dematerialized was shocking, stark. it did not disappear gradually. the best way i can describe is that it blinked out as if a light blub turned off. it was there and in the smallest possible observable instant it was not there.