Boomerang or Triangle shaped air craft with large round lights that did not give off illumination, traveling slowly across the sky

In 1976 or '77 when I was 15 or 16 several people witnessed a slow moving air craft which was 'boomerang' shaped in the night sky. Do not remember seeing a bottom connecting side which would have made it a "triangle" shape. It cruised slowly across the sky and did not seem 'powered' as it was silent, gave off no emissions, and had no visible means of propulsion (wings, engine, propellors). It was about 1500 yards above, was very large (certainly bigger than a conventional plane, hot air balloon or helicopter-which it was NOT). There were large round orbs of light which did not give off any illumination at all down the two sides. Did not feel necessarily threatened although the sight of it was alarming. Everyone was amazed at what we were all seeing. I myself ran home quickly and called the police. I remember the officer who answered was male and said something to the effect of 'we're getting calls, we know about it, checking on it but nothing to worry about'. And that was basically it. Though about it over the years every once in a while until... While surfing Amazon Prime I happened on a video entitled "The Phoenix Lights UFO's". I almost fell out of my chair as the footage was EXACTLY what I saw in 1976 (or '77, not quite sure) over Brentwood LI on the grounds of my elementary school. Would love to connect with anyone else from Brentwood who remembers this. As this was totally unexpected and before cell phone cams, I have zero documentation.