Star like object on northerly course makes 120 degree turn, moves erratically and stops, vanishesI was on the balcony of my hotel in Cancun at approximately 11 PM, Saturday, April 21st, stretched out on my back, looking straight up at the stars. I had never been to Cancun and looking at the sky between sets of a card game; the stars were more clearly visible than in Seattle, where I live.After a few minutes of looking at the stars, I observed what appeared to be a medium-bright star moving in a nearly due north direction. The object moved at the same speed and at first I assumed it was a satellite or a plane, perhaps. Then, it abruptly changed course (without stopping) approximately 120 degrees to a southeast direction. It then began to make erratic, darting sort of movements, accelerating and slowing, moving in different directions within a relatively small area of the sky, before appearing to come to a complete stop. A couple of seconds later, it vanished. This entire episode lasted approximately 20-30 seconds. I did not lose sight of the object until it disappeared.There was one witness, a friend of mine on the deck with me. Two other friends on the deck did not see this phenomena in time before it disappeared. They could not pick out what I was pointing at. I alerted my friends to the phenomena when I saw the initial 120 degree turn, as it was an extraordinary movement of an object in the sky.It was easy to discern the motion of the object, as there were palm leaves just below my point of reference, so I had a clear definition of the object's path relative to my surroundings. It was perfectly easy to track the flight path of the object, there were no obstructions and I did not lose sight of it during the sighting. The sky was clear, with few if any clouds. Other stars were visible in the vicinity, none were moving. If it had been a mylar balloon, as was suggested, caught in the breeze, it would have likely changed the intensity of light reflection as it moved, but this was a solid unblinking light, exactly like a medium-intensity star. A balloon would not have moved in such a perfectly straight course for the 8-10 seconds I saw it before the initial course change. There were other stars of that intensity out that night; it was easy to compare its brightness to other objects in the sky. It was not as bright as Venus or as dim as a star you'd have to squint to see. At first, my friend thought it was a satellite because of the brightness, until its movements were clearly not that of a satellite. It left no trail as a meteor would; I sometimes sit out and watch the Perseid Meteor Shower when it occurs in the summer and am familiar with what a "shooting star" looks like. I have seen satellites pass overhead and the luminosity was comparable to a satellite or a medium-bright star. Venus was visible that night to the west, nowhere near the flight of this object. Mars was also visible; it was neither of these planets. We watched the skies for about twenty more minutes, and did not see anything like this again. There were no apparent laser light shows in Cancun, as anything of a promotional nature would have likely been repeated in the time we watched the skies after the initial sighting. We were sober and alert when we witnessed this object. My eyesight is 20/20 corrected with glasses, which I was wearing at the time. I work in engineering for a large telecommunications company, and my friend who witnessed it is also a professional employed in project management. The two others who did not see it are a CEO of a financial institution and an automotive project manager. I do not consider myself a UFO buff, or a believer for that matter. But what I saw, a star or object that made an approximately 120 degree shift in course instantaneously without stopping, quite frankly, startled me. I feel a little embarrassed telling people what I saw, because I have received a bit of ridicule already by telling a story like this. I am not claiming to have seen a UFO, I did see something exhibit motion not possible by our understanding of physics. I don't know what it was, but it was not a plane, a meteor, a bird, a balloon, a star, a satellite or a reflection of anything. The sky was clear all around our area. I am also not known as a storyteller, someone who seeks attention. I wasn't looking for a story, I was enjoying the stars. Until I saw this phenomena. I don’t know what it was.