From the ground on a clear afternoon, is there any known optical illusion or effect that could make a single helicopter appear to be two helicopters, stacked vertically?
(Besides crossing your eyes. I’m serious.)
You could probably get something like that from a mirage, though the layers of air would have to be just right.
Is the helicopter close to the horizon, and is one of the helicopters flipped vertically? If so, it could be a fata morgana mirage.
As the digram you linked to in fact shows, a fata morgana can produce both inverted and upright images, so I think it is very likely that this is what brujaja saw, whether one of the helicopters appeared flipped or not. Several stacked images are possible, but you may not see all of them.
When I was a kid, I once saw a fata morgana over the Thames estuary in southern England. A distant ship appeared to be floating in the air, upside down, above itself. I have never forgotten it. Very weird.
You guys are awesome. I knew there would be effects, with names, that Dopers would know.
This is complicated by the fact that there were actually three helicopters, in three different positions, but I expect it was some kind of formation because they were monitoring the tense situation in downtown Oakland.
They were each quite still; then I noticed that it really looked like they were spraying something, because from each of them came a sort of mist that happened to catch in the sun and glow golden-colored.
As the mist dispersed, I saw a second heli sort of fade into existence above each one, directly above but set back a little bit. Frankly, I would swear that I saw all six moving somewhat independently of each other, though staying pretty much in pairs. I was so dumbfounded that I watched them for several minutes. I even covered one eye to make sure that it wasn’t some artifact of binary vision.
Then as I watched, the second set of helis, vanished, poof! Freaked me the hell out.
That’s true, although my understanding is that the distortion is continuous–the bottom of an upright image can’t directly “touch” the top of another upright image; there must be an inverted image in-between. However, this image might be compressed to the point of invisibility, or simply be obscured by clouds or something.
Very cool. I’ve seen the illusion, but only as a funhouse-mirror type distortion of distant objects; never as a clear upright or inverted copy of something.
The “mist” you saw might have been another effect of the mirage.
I just have to point out that “fata morgana” is one of the coolest sounding names for an optical illusion I’ve ever heard.