Not all flying saucers are from outer space. The sky will occasionally snag on itself, leaving a saucer-shaped rip.
Whenever the air is tearing itself apart, the resulting sky-snag will take on the shape and texture of a metallic disc. As the sky splits apart, lights will shine out from the laceration. Because of the wind, a rip in the sky will move around and about as if it were a sailing vessel of some kind.
The sky, like everything else that moves, is an accumulative effect from the vibration of many separate ingredients. Radiation, dust and gas. Nitrogen, oxygen, carbon dioxide, argon, neon and the like. With all these ingredients bouncing about were is wear and tear. With the friction of rubbing, scraping and flowing the air will, on occasion, burst seam. The rip will wrap around itself, forming a concave surface with an inherent polish.
Because of the many ingredients involved, sky-snags are occasionally accompanied by fire and smoke. Because of all the turning and winding and twisting of the many ingredients involved, these tears can also be accompanied by many different types of noise. The involuntary turning, winding and twisting of the wind will hold and direct the motion of the tear. Randomly, throughout the local sky.
Entropy in action; as the ingredients, that once made up the saucer-shaped tear, blend back into the over-all general effect that is the sky, the sky-snag will fade, as if by great velocity.