It is immediately noticeable that the visual LOSs to the UAPs from the Trislander were not far from the azimuth of the sun. This fact was indeed noted by the witnesses, two of whom also described the light as "sunlight" coloured n1 One of these nevertheless thought that the source was emissive, not reflective, and this witness along with one other mentioned "orange" hues, suggestive more of haze-scattered sunlight than direct light from a high sun.. This coincidence invites speculation that the UAPs may have been caused by some kind of atmospheric-optical reflection or refraction effect.

Sundogs (or parhelia) became a favourite hypothesis of some public commentators within a very short time of the event n2 On the basis of early newspaper stories a local author, Michael Maunder, published the sundog theory in the biweekly Alderney Journal, volume #873. A letter in response from Capt Bowyer appeared in #874. Mr. Maunder retracted the theory on the basis of information provided by Capt Bowyer and by the present authors. He appears to have reverted to a version of it in A Report on the Putative UFO Seen Over Alderney, Maunder/Speedybrews 2008.. Sundogs are fuzzy patches of light caused by refraction of the sun's rays through hexagonal platelet ice crystals above the observer. We were easily able to confirm the presence of ice clouds above the ~10,000ft freezing level (Fig.22 & Section 5), thus between the Trislander and the sun. But not below the Trislander (air temps >10°C) and so not on the observer's LOS to the UAPs near the horizon.

The optical geometry dictates that sundogs occur close to the 22° halo around the sun. They tend to be elongated with the major axis of symmetry lying vertically because of the way the ice plates lie in the atmosphere, but do sometimes show spectral "tails" extending radially away from the sun, to left and right, for a degree or two. But a pair of sundogs would bracket the sun at about 45° elevation above the horizon, about 22° either side of the disc n3 In fact sundogs are bright nodes at the intersection of the rarely seen circumscribed halo and parhelic circle, and the higher the sun the further out the sundogs will appear. In this case they would have moved out several degrees from the 22° halo along the parhelic arc, appearing subjectively even higher.. Two lights near the horizon, almost directly below the sun and just a few degrees apart, are not sundogs. We can be confident of this on the grounds of the gross geometry without going on to consider their "brilliance","extremely well-defined" outlines and curious internal detail.

Fig.22. Brest radiosonde ascent, noon, April 23 2007, showing freezing level ~3200m. The frost point is the temperature (slightly warmer than the dew point) at which saturated air begins to condense preferentially over ice particles. (graph courtesy Dr. Robin Hogan. Reading U.)
Fig.22. Brest radiosonde ascent, noon, April 23 2007, showing freezing level ~3200m. The frost point is the    temperature (slightly warmer than the dew point) at which saturated air begins to condense preferentially over ice    particles. (graph courtesy Dr. Robin Hogan. Reading U.)

The common sundog is only one of an array of light halo phenomena that can be caused by ice crystals, but most of these are even fainter and consequently rarely seen. In rare conditions such as most often occur in polar skies a complete display can be seen with a whole complex of superimposed arcs and nodes of increasing fugitiveness at larger angular distances. There is even a faint secondary halo occurring at 46° from the sun, which could at least have intersected the horizon in this case (had there been ice crystals present at low level). But none of these phenomena resembles the UAPs reported.

It would be possible - given the presence of a layer of ice crystals below the observers - for a brilliant terrestrial source (such as a reflection of the sun from the sea) to generate a 22° ice halo and also to appear flanked by a pair of "sundogs" ~44° apart. But the reflection geometry, like that of a rainbow, is always fixed in relation to the positions of the observer and of the source, and the internal angles between the nodes and arcs of the halo do not change, whereas our UAPs (which were of course neither 44° apart nor each 22° from any visible bright source) moved laterally relative to one another by several degrees.

The sundog hypothesis is also not very useful to explain the Jetstream pilot's observation on a near reciprocal line of sight, looking away from the sun. The only remote possibility for explaining an object on this bearing as an ice halo would be a 120° sundog on the complete parhelic circle. In a very well developed parhelic display there are in principle two of these paranthelia , 60° either side of the anthelion (a faint patch on the parhelic circle opposite the sun), therefore at 345° and 105° azimuth. It seems possible to reconcile a 345° azimuth with the pilot's 8 o'clock LOS within 10° or so.

However these rare paranthelia are faint elliptical blurs of light not much brighter than the parhelic arc they sit on, which would also usually be visible, and more importantly the elevation of the parhelic circle is that of the sun, i.e. in this case ~ 45°, whereas the UAP was observed at a depression angle below the horizontal. This theory doesn't fit the pilot's description of a"yellow/beige" oval in any particular.

Plausibility (0 - 5): 0