I was lounging in my hot tub staring up at the stars. It was a clear night sky's with only a few scattered whispy clouds. Something unseen and large, blending in with the dark sky, appearing to be within several hundred feet away, moved out from behind a group of clouds slowly moving towards another small grouping of clouds. I only noticed it because it began blocking out my view of the stars behind it, moving at a steady rate (about the speed of an airplane at high altitude) towards another small group of clouds. The outline of this object was distinctly geometric, potentially triangular in shape on the travel direction side. Size wise, assuming this was within 300ft or so, had to be the size of a baseball field (maybe larger) and similar in shape. I've never seen anything like this. Whatever it was was completely invisible to the naked eye, it perfectly matched the sky behind it but for the stars dimming out behind it. I will admit I was terrified. My heart nearly stopped. I immediately went inside. For geography, this occurred in Tulsa, Oklahoma in a SE neighborhood behind [ADDRESS].