Black triangle, no noise, impossible mobility for its size, sighting lasted 45 minutes.I was walking towards my house with my headphones in and my coat hood up, when something in me told me to look up and take my headphones out. Amazingly I was facing a black triangle, hovering a few meters above some houses, regularly changing in shape and size.When I first saw it, it was roughly the size of half a football pitch, it was so terrifyingly large that it knocked the breath out of me. I rang my father and described what I was seeing, during this I started hysterically crying and laughing, because I totally could not believe what I was seeing.It started as an irregular triangle, with the tip pointing diagonally down towards the houses, it's surface was parallel to me so I was able to see a light in each corner, these pulsated between being as dim as stars and as bright as floodlights.Over the course of 30 minutes of standing at the end of the road watching it, it slowly moved up and down in the sky, sometimes dropping so low that it disappeared behind the houses. It also changed between irregular and equilateral, also changing in size from its largest being roughly 34m in length to its smallest - the length of a small car.I decided to continue on my way as I had already been there a good while, once I reached my house (15 minutes later) I looked back and it was still there, in total I watched it for 45 minutes. It made no noise, put out no other light except the three on its corners, and managed to remain completely stationary in the air.That, paired with the constant feeling of pressure on my ears, assures me that this was something other than a man-made object. I also noticed that no other aircraft passed over during the entire duration, over which is normally an incredibly busy air traffic route.I'm was still shaken for a few hours after this, from excitement and fear. But now I think about how lucky I was to see it, truly a humbling experience.