I was nearing the end of a flight from Calgary Canada, to London Gatwick airport. I had a window seat facing to the left of the aircraft. We had just flown over England, and had just turned from flying east along the southern coast to heading north towards the airport. We were around 500ft+ above the ground but it was close enough for me to observe cities and roads from a great height. I was minding my business just looking out the window and a metallic sphere caught my eye. It was completely spherical and was traveling at a great speed. It did not appear to make a sound or have any visible form of propulsion. It was simply a metallic sphere flying at a great speed, however fast enough to be observed. The total time of the encounter lasted about 6 or 7 seconds. Id been watching UFO hunters recently and I thought that it must be weird to see something in the sky and instantly know it wasn’t normal or that it didn’t make sound. I wouldn’t say I’m a skeptic but I just found it all very interesting. Then I stumble across this sphere. I can guarantee 100% that I was not mistaken for any kind of helicopter/aircraft. There was no propulsion and it was moving silent very fast. Its interesting because most UFOS caught in daytime are Triangles over California. So to see a sphere is very different, and unlike a triangle, there is no relation of a spherical craft to any current aircraft models. It is possible that the object was disc shaped but I was observing it directly from above (making it appear spherical) the craft moved at an incredible speed. NOTE: The above image is a rendering.