Approximately 2040 hours i entered the hot tub on the back deck of my house all exterior lights were off providing a good view of the night sky. clear night no wind. observed a jet plane from north to south travel while watching noticed a bright light appear over the western mt. range. i am 85 mile west of d.C. in the shenandoah valley, va live in a 3 mile wide valley with large mountain rages to the east and west. the bright light resembled a helicopter with the search lights on but seemed to be brighter moving slowly to the east in a straight line. turned off the ho tub jets with nothing audible the night was completely quite. light was huge and appeared to be low flying about the height of a helicopter. i couldn't make out a shape due to the brightness of the light. traveled halfway across the sky and abruptly turned 90 degrees and accelerated speed dramatically straight away from me quickly growing smaller and smaller to a pin point and then nothing. acceleration viewing about 3-4 seconds from a large white/amber light to nothing. i've seen unexplained lights in the sky but this one defies logic with the movement, change of direction and extreme acceleration in speed. left me stunned for a long while.