very low flying diamond making no sounds

I’m not exact on the year but it was a summer night with crystal clear skys, around 10pm. I was standing outside when the sky above turned black.  The contrast between the craft and the sky was what made me look up. I have never seen anything so black before,  The craft covered the entire house at one point and only flying at treetop level. The thing did not make a sound! It had bright lights on each point and a large light in the middle. I could not move for about 10 seconds, just out of total disbelief.  I then ran inside the house screaming for anyone who was home and was only able to grab my mother who went outside and also observed the craft.  The craft was moving so slow, and so low I could have hit it with a rock. It proceeded east crossing over the New York State Thurway, not making a sound.
Witness indicates that the date of the incident is approximate.  PD