Sun bright object seen high in the sky near Air force Academy disappears in seconds!

While driving South on Interstate 25 and passing by the Air Force Academy, I noticed something very bright out of the corner of my eye.  Looking out my car window there was this ball of extremely bright white, (like looking at the sun), light.  It was very high, I would say at a hieght of around 35 to 40 thousand feet.  It was off to the east at about 10 miles and disappeared over the horizon to the South in about 4 to 5 seconds.  I heard no sound nor was there a contrail.  I told my wife we have just seen a UFO.  Being a private pilot and former USAAf/USAF aircraft mechanic, I know what conventional and military aircraft look like because as such we pilots can't help looking up when we hear an aircraft.  I would just like to add that this was not the first nor the last time I have seen strange objects in the sky.
Witness indicates that the date of the sighting is approximate.  PD