I observed a plane flying so high that it was just a point of bright light and its vapor trail. I would guess its altitude was 50,000 feet. It traveled 45 degrees in my field of vision, limited by trees in approximately 1 minute. That works out to about 700-800 mph if you do the math.Immediately as it disappeared beyond the tree line, another bright white dot riding very near, almost in, the first plane's vapor trail made that same trip in 5 seconds. That works out to 48,000 mph. Both objects were so high as to be indistinguishable as airplanes. just appearing star-like as bright white dots. Several nights later I was observing the moon with a 10X binocular when I saw a similar bright white type dot race across the sky in about 3 seconds. This time the unobstructed angle of view was about 120 degrees. I have never seen anything travel so fast in all my years observing things in the sky.