Oscillating black-ish/gray spherical object hovering in ther sky and disappeared

Last night, my 3 friends and I were on the roof in Manhattan.  We had a few bottles of wine, so we were a little warm, but not incoherent.  It was bright out because of the supermoon, so we had a clear view.  
My friend, who pointed in the air, then told us to look.  3 of the 4 of us saw what looked like a thick blackish-gray disc, hovering in the air a few hundred feet out.  It was not a plane, because we had seen many moving around that night.  
I thought it was a balloon floating up but my friend and I stood up and approached the edge of the rooftop to get a better view and I quickly ruled that out.  What I personally saw was something that looked large enough to not be a balloon, and it was definitely oscillating.  It made no sound, but I did not expect it to at our distance.  
I rationalized at first it was a balloon floating from the light into the atmosphere and thus disappearing, but something was off about that idea.  However, as I approached it went from a darker color to gray, and then disappeared almost as if backing away.  
We all 3 were very creeped out and thought it was a drone or definitely a UFO.  
Still thinking about it, but it moved so quickly away once I approached it, I couldn’t really process things.  
Anyway, definitely saw a UFO last night and first time I have ever posted something like this.