Huge flying silent and very slowly, very low down from the sky,

In evening, I was standing outside, on that date there was a powercut, blackout in whole of northern Ireland, this low flying craft was really black, it stood out in the dark sky, but at the time I thought it must be a mother ship!! I was young at the time, but I was at the airport few months later, I saw a Boeing close up, I was impressed but I remember thinking it still was not as big as the triangle, I would like this to be noted