Twenty years ago I was doing some field work mapping an area north of here along the base of Front Range of the Rockies, where several ridges parallel the mountain front. It was a day much like today: cold, but with a strong downslope wind blowing.

As I'm wandering a ridge top, I looked to the west and saw a strange object floating towards me, several ridges west of my position. It appeared to be a clear tetrahedron. The wind took the object up and down over the ridges, always staying about a hundred feet off the ground and rotating in seemingly random ways. I watched it with my field glasses until it passed directly overhead. From this vantage I could clearly see that it was a large plastic garbage bag (like the ones used to line a 55 gallon drum) that had been sealed and inflated in a way to create a tetrahedron. (If you think about it, it would be easy to do: take a plastic bag, open it, but then close the top of the bag 90 degrees away from how you'd normally close it. This creates a tetrahedron. Seal with a heat sealer and inflate before closing the final inch of seal.)

As I watched it disappear over the ridges further east, I had to wonder. Why? It was obviously man-made, but was it joke, an experiment, or what? Never did find out, but I've been waiting for someone to make such a thing and use it as a hoax. Imagine using a black plastic bag with some light-weight LED's at the corners! That'd look really cool!