My family and I were on vacation in Costa Rica at a resort near Culebra. It was the last night we would be there and so I decided to go down to the beach and stargaze, which I do often. This was sometime around 10 P.M., but I am not sure. The moon was due SW and was around 55 degrees above the horizon, probably higher but not lower. That might indicate a time. I spent probably 25-30 minutes there before heading back, as I couldn't see much due to the bright moon. While walking back to the buildings (perhaps a 2-3 minute walk) I decided to look for the brightest star in the sky, something I also do often. I found it immediately, approximately 70 degrees above the horizon due NNW. It was somewhat brighter than Jupiter would be on a clear night, but wasn't so unnaturally bright as to be immediately recognized as unnatural. While it was a mostly clear night, some stray clouds (cirrostratus, I think) were in the sky. They weren't thick, but they did obscure the stars around the object. It was clear that the object was behind the clouds, which is what made me interested in it. This star, or object, was sufficiently bright from behind the clouds to still be the brightest in the sky, and with a bright moon. I stopped walking to stand there and watch the clouds move away from the object, taking around 10-15 seconds. Of course, the star-object became slightly brighter as a result. Then, as I watched, it suddenly accelerated to the left, or West, and disappeared. The acceleration was unlike any I have seen, going from no movement to an incredibly high speed in apparently less time than human eyes are capable of seeing. It moved an unknown distance, but if I were to make a "peace" or "V" sign with my index and middle fingers, and held my hand out as far as possible, it would have appeared to travel the distance between those two fingers. Or, at arm's reach, around 2-3 inches. It traveled that distance in about 1/2 of a second. At the end of that distance, it continued, but it was now quickly fading while moving left, with no apparent change of velocity. That took only 1/4 of a second. It is possible that the disappearance was the object leaving Earth's orbit, and that the object was ascending while moving West. After that, there was no more sighting and I slowly walked back to the resort. I then felt amazement at what I had witnessed, immediately convinced that it was either from some origin other than humans, or that it was some incredible new human creation. Either way, it was clearly not the following possible explanations: 1: A conventional military aircraft. It hovered, not possible for planes, and it's velocity was too high for a VTOL. Not to mention that the acceleration the object would not be possible for any known aircraft, and for several reasons. 2: A space station. While space stations can appear as bright stars that move, they cannot be unmoving, be unmoving and accelerate, move that fast, or disappear. 3. A meteoroid. While an object such as this, when falling to earth, will certainly travel very fast and then disappear, it would not be unmoving and then suddenly accelerate. A summary: An object, appearing as an unusually bright star, is visible behind cloud cover. It maintains its position for over 10 seconds before suddenly accelerating, apparently instantly, to an incredibly high speed. Then, while keeping its speed, it fades and disappears. I attached a Google Earth view of the bay I was in, for your use. I would like to state that I was under the influence of no drugs, alcohol, or other agents that could have caused me to see things that weren't there. Please do not hesitate to contact me via email for clarification or follow-up. Thank you.