While camping a couple days ago, I saw an UFO. I saw this object yesterday (July 19) at around 11:00 pm. A bright light which I at first thought was Venus (it was by far in the wrong position than Venus and was quite a bit brighter, however) was moving at a constant speed. After about five seconds of viewing this object, the light emitted by it shrunk to a small size which would be pretty hard to see had I not already known its position. It continued to move at around the same speed as it had before until it went behind the cloud of a dissipating thunderstorm and disappeared from sight.

What I'm looking for are some possible explanations of this phenomenon. My guess is that it was a satellite reflecting light from the sun more so than normal, which then ceased being at the proper angle to reflect as much light as it did, and then looked as it normally did after it moved out of this critical angle. Any other ideas of what this object may have been?

Maybe the space station?

I saw something similar to what your describing except it was slightly above Venus (at about 10:15pm) back this past June and someone told me it was the space station.