3rd & 4th order rainbows

Unlike the ice halos discussed above, rainbows are water droplet phenomena 1 A useful and authoritative source of information on a wide range of light effects involving droplets and crystals is the atmospheric optics website of physicist Les Cowley. A wealth of data and applications is also available. The common primary and secondary rainbows occur around the antisolar point, which is the vanishing point of a line drawn from the sun through the eye to the point on the celestial sphere opposite the sun. The primary rainbow appears as an arc of a circle 42° in radius. Clearly phenomena observed at the sun's azimuth cannot be primary or secondary (1st and 2nd order) rainbows.

There are however rarer 3rd and 4th order rainbows which do occur in the direction of the sun. The 3rd order rainbow is only about ¼ as bright as the 1st and the 4th order about 1/6 as bright. They are almost never visible because of the glare of the sun, but in ideal conditions with the sun occulted it is thought that they may very rarely be detected. The 3rd order bow occurs at the same radius from the solar point as the 1st does from the antisolar, about 42°, and the 4th occurs immediately outside it separated by a small gap, with the order of colours reversed.

In this case we can perhaps suppose that direct sun at ~45° elevation is shielded by cloud and by the top of the cockpit windscreen, and a 42° radius would bring the bows close to the horizon. Perhaps only a small, isolated segment of bow is caused by an isolated patch of rain droplets. There is also a region where the inverted spectra of the two concentric bows abut, in the red, which might appear as a dark area between brighter yellow regions, suggesting the idea of the "dark band” reported on each of the two UAPs.

But these 3rd and 4th order bows are even broader than the common 1st and 2nd order ones and the pair would be perhaps 5° in thickness, an order of magnitude bigger than the 0.5° width of the UAPs when first observed, and the possible dark(red) area is much too wide to be a dark band in the order of 0.1° degree across or smaller.

Also to get the reported "brilliant” and "clearly defined” shapes from these very faint and elusive phenomena near the glare of the scattered light from the sun seems quite impossible. And even then the hypothetical "dark band” in the red must appear on a circumferential arc concentric with the sun; but because our UAPs are almost directly below the sun the band would lie horizontally, not cut through the UAPs vertically as observed.

Finally these bows can't occur in the absence of raindrops. Available meteorological reports and weather radar scans (Section 4) do not indicate rain in the sighting area 282 Fogbows can be caused by suspended droplet sizes smaller than raindrops, but they are far too diffuse and faint for our purposes. However see Section 6d..

Plausibility (0-5): 0