Saw a large triangular black silhouette moving very slowly (maybe 5 mph) approx 500-800ft in air completely silent one solid red light.

I was about to go to bed and had the window open facing West and saw a large aircraft moving north. What gave me pause was the size, the shape, and the fact that there was no noise. It was a large triangular shape, solid black silhouette with a single red light. It was approx the length of a football field and seemed to be above the Hudson River which is less than a mile from my house. It moved as slowly as large boats do maybe 5-10 mph. Like a blimp. No sound at all. But it was a large vertical triangle. Maybe 500-800 feet above ground. I was trying to figure out what kind of aircraft it was but after it passed and noted it I can conclude I have never seen anything like this before. Since West Point is close and we have military aircraft travel over us from time to time I figured it initially might be something military related. But after some research it seems like there are no aircraft that size in that description.