Dark, spherical object 50 ft. above tree line silhouetted against evening sky in residential neighborhood.I was on an evening walk not far from my house, when I turned in a westerly direction on a residential street. The time was around 21:00 hours EDT on the date of 7/08/2017. As I walked generally towards the west, I saw a dark, round object silhouetted against the still bright western sky. It appeared to be about 50 feet above the tree line at a heading of WNW from my location. It was motionless and emitted no lights or sound. It also appeared to be slightly wider than it was tall but was generally spherical in shape. It seemed to be about the size of one of my fingernails, held at arm’s length, from my perspective.The first thought that came to mind was that I was observing a large tethered balloon some unknown distance away. I also considered a kite but quickly dismissed that idea as there was barely a breeze and certainly not enough wind to keep a kite aloft. I continued to walk westerly as I observed the object for about 10-20 seconds before the tree line obscured my view. In that time, the object did not appear to move at all, but remained completely stationary. I continued to walk to the end of the street and turned northerly at an intersection. As I walked farther I tried to again observe the object through breaks in the tree line towards the west but to no avail. The object was now gone.This is the first time in my life I have ever seen an object in the sky that I could not identify. It did not appear to be a helicopter, plane or drone and (to reiterate) was completely silent. It appeared to be much too small to be a hot-air balloon, and I have never seen hot-air balloons floating over my neighborhood in the past 4-1/2 years I have lived here. Therefore, I am mystified as to what it was.