Jet black triangular aircraft at close quarters

I was stargazing, laying back on a chair. The Stars seemed to disappear, but I here were no clouds in sight. As my eyes adjusted, I could see a perfect triangular aircraft that slowly manoeuvred over my head, literally just skimming the roof of my friends house and move down the garden. I followed it, directly underneath it. It completely quiet and had three circular dimmed lights on the back on each corner.

I tried to look over it and see the depth of this thing, but it looked completely flat as it moved towards the mountain. It wasn't a drone, as I have tried to find anything that resembles it. Nothing has come even close to resembling this craft. I'm reporting this now, as came across a documentary that says there were mass sighting that year and I didn't want to go to the police, for fear of looking crazy.

It was about the size of a small regular aircraft. I think there was a very low hum to it and it mad the hairs on my arms stand on end.