Back in the early eighties I was an instructor at the Oxford Air Training School. One day, whilst flying with a student in the local area over Otmoor I looked to the left and saw what appeared to be a dullish red sphere about the size of a football keeping station about half a wingspan off the wingtip. I pointed it out to the student and asked him to turn towards it. Whatever we did with the aircraft, that sphere maintained exactly the same relative position. After a short time, our atention was distracted by something and when we looked again, it was no longer there. I didn't mention it to anyone else at the time but I've often wondered in the intervening years what it was that we actually saw.