Hovering, illuminated, white oval gradually disappearsI was standing in a pasture. It was at dusk, the sun had set below the horizon for only a minute or two. The sky and clouds were still somewhat illuminated.To the west, near where the sun had just set, I witnessed a stationary, hovering, illuminated, white oval shape. It appeared as if the entire shape was illuminated evenly. From my observation, it did not appear to be reflecting sunlight, because the sun had already set, and the object appeared to be in Earth's shadow. At the time, the object was the brightest thing in the sky. Although the moon was not visible for comparison, I would estimate the object to be about 1/3 of the full moon's size.The object appeared as a white oval. It may have been a lenticular shape seen on edge (like a white Mentos candy), but I could discern no 3D shape to it. It did have a clean edge. The object was also perfectly symmetrical, with no bumps or irregularities in the shape. I observed it for approximately 15-20 seconds, all the while using my powers of logic and reasoning to determine what I was looking at, but was unable to do so.As I watched, the object began to disappear. It did not shrink in size, recede, blur, or blink out. Instead, it appeared to become gradually more and more transparent (evenly, while retaining its clean edge) until it was no longer visible.Though I am not trained in aerial observation, I am reasonably intelligent. In my opinion, what I witnessed was not any sort of cloud, celestial body, or other natural phenomena. Nor was it any type of man-made aircraft that I am aware of.Other, more subjective notes: I was outside shooting a firearm at the time of the sighting. I was shooting at a target to the north. A thought entered my head, something along the lines of, "What if you saw a UFO right now?", then I looked to my left, and there one was. I feel as though I was somehow compelled to look in the direction of the object, and perhaps it had something to do with the fact that I was firing a gun. This is purely speculative.Later I thought about the fact that I was in the town of Ovalo, Texas. Ovalo means oval in Spanish. What I saw would definitely be described as an oval. Not sure what the connection is there, if any.((NUFORC Note: Witness indicates that the date of the sighting is approximate. PD))