Summary : Smooth, rounded triangular object, stone grey, no lights or markings, dome on bottom, silent.I was 'camping' in the backyard of my friend of the time in the Blackfoot Idaho of 1973.My friend told me there was a UFO in the sky, come look. I figured he was lying. He became deathly serious, and told me that if I did not look, I would regret it forever. His tone scared me, so I looked.Up in the 3 am sky was a smoothly moving object. It was the size of my right thumbnail on my outstretched hand.The object was perfectly silent, a rounded, smoothly contoured equal edged triangle. It appeared to have either a dome shaped hollow or protrusion in the middle bottom. There were no lights, seams, markings, or details whatsoever.It appeared as though cast of one solid piece of material. It was the grey of stone, and was visible by virtue of the reflected glow of city streetlights upon it. It moved in a perfectly straight line, with no 'point' of the triangle facing the direction of travel exactly. Near the zenith of our view, it suddenly altered direction without curving or slowing down.One second it was going one way, the next instant it was moving about 35 degrees or so another way. It contined on this slow, smoothand straight new path, until it was lost to sight behind trucks parked near us. I saw the object go past telephon and power lines, it was above and behind them.My friend and I decided not to speak about it, but instead to immediately go inside the house, and seperately draw and describe the event on paper, then exchange the papers.We though this would let us know that what we saw was 'real'. Our reports to each other, when finished, were identical, except for one difference.I had thought the dome on the bottom was a 'hollow', not unlike the 'dimple' in red blood cells, while he thought the dome protruded outwards from the rounded shape. I ascribe this to the difficulty of percieving an unfamiliar contoured shape in reflected light from distance.The event lasted approximately 4 minutes in total, from the time I started looking, to the time the object glided silently beyond our vision.During the event I measured the object with my thumb, and closed my eyes briefely to see if it would still be there when I opened them, it was.The sky was perfectly clear, and the stars shone brightly. Our shared yard was surrounded on all sides by large trucks, houses, a fence, and trees, making for a perfect viewing environment,with no directly visible light sources to spoil our view. I was 13 years old at the time, my friend was 14.I have never forgotten this sight. It was utterly unique. I have no feeling or impression whatsoever about what the object actually was. It could have been anything from ship to lifeform to paradimentionalprotrusion to shared, perfect hallucination. Any of these explanations are equally fantastic. It simply...was. Featureless, solid, grey, and oblivious tothe way objects are supposed to move.I have not seen anything else, since. I have certainly seen nothing else like it.It taught me a few things: one, that during a genuine sighting it is utterly impossible to hope to realistically describe thesize of a UFO, as there is no yardstick by which to measure it, save one's own arm, or a nearby object. Against the starry sky,such a thing could have been any size (within reason) and almost any distance away. There is litterally no way to tell.Therefore I discount the tales of folks who claim to know the distance and size of an utterly unfamiliar object.Lastly, I feel a little cheated. In the years that followed this event, I have heard many tales of UFO sightings, all with fancy lights,weird sounds, strange feelings, and so forth. My sighting was not so spectacular, just a blank, seamless impossibility,moving silently. It did at least move in an impossible manner, which is at least something!I cannot remember my friends name after all these years, alas. I hope that this report may cause him to contact me,so that I can reminisce about this event.