|Date: Sat, 27 Jan 2001
From: Brad Sparks
Subject: Re: BOAC Case Analysis
In a message dated 1/27/01 3:34:16 AM, LorenGross@aol.com writes:
>Sign Historical Group -
First problem is that the terrain was not flat but mountainous. A mirage would have to form in a layer of stable atmosphere low in altitude and near the earth's horizon as seen from the BOAC airliner. The earth horizon was about 250 miles away to the west-northwest over the Otish Mountains. Mountain updrafts tend to disrupt air layers.
Atmospheric physicist James McDonald concluded "No meteorological optical phenomenon could reasonably account for the reported phenomena."
The Condon Report also concluded that the sighting could not be explained by mirage (CR pp. 139-140).
The pros and cons for mirage are:
1. The dark images seemed to change constantly as if unstable, and at the end the 6 satellite images merged into the main image, then grew small and vanished. This seems like "mirage behavior" at least superficially.
2. The 6 satellite images always stayed horizontal even as they seemed to move around the main image. Horizontality is a sign of mirage conditions.
3. The BOAC airliner stayed at the same height, 19,000 feet, throughout the sighting, which might have kept it at the same elevation angle relative to a mirage layer.
4. The images _seemed_ to stay at about a constant angle or direction from the descending sun low on the horizon about 5 degrees away to the left. (The sun was low in elevation at about 5-7 degs above the apparent horizon and dropped to about 3 degs at the end of the sighting.) This is suspicious but hard to exactly reconcile with a mirage. It is also an inference from McDonald's summary of the case but not directly stated by him or witnesses so far as is known. (McDonald says the UFO was about 5 degs to the left of the sun and doesn't say if this relative position changed, so I infer from that it didn't change.)
5. There is a somewhat similar aircraft case, the Gander / Bethune case from the same general region on Feb. 10, 1951, involving a round light at one point seen as a circle of lights or like an "eclipse," which has been explained by Phil Klass as the setting crescent moon. I once thought that the moon could be ruled out based on the time and location. But additional file documents and recent testimony from Graham Bethune have thrown so much doubt into the exact times, locations and headings that the moon can no longer be ruled out, but it is still difficult to explain.
1. Mirages are "anisotropic" -- they are not visible in all directions -- as the Condon Report discussion of the case by physicist Gordon Thayer points out (CR p. 140). Slight changes in viewing angle make mirages disappear. Normally mirages are seen from a stationary location on the ground. Here, the BOAC airliner was travelling at about 270 mph. If the airliner had been travelling straight towards the UFO's thus maintaining at least the same direction angle then the mirage theory might be more tenable. But the UFO's were seen at nearly _right angles_ to the airliner's path. The BOAC airliner was heading North-EAST but the UFO's were to the North-WEST (or WNW).
2. Mirages are not images of air, but of actual objects seen through the distorting layer of air, such as terrain features, ships, sun, moon, stars, etc. Even if the BOAC airliner had been travelling straight towards the UFO's -- which it wasn't (see above) -- so as to improve the chances for mirage imaging, the long 18-22-minute duration of the sighting and great distance covered in that amount of time (about 90 miles) would change the elevation angle to some distant object being imaged by mirage.
The change would be about 1.3 degrees, and would have caused a mirage to disappear long before the UFO's disappeared, probably within 5-10 minutes of such headon travel or less. The reason is that the critical elevation angle for mirages is about 0.5 degree from horizontal due to the maximum refractive gradient that is possible in the earth's atmosphere, a "grazing angle of incidence."
As the Condon Report chapter on optical mirages states, "For all practical purposes, 0.5 degree can be considered as the near-maximum angle of illumination that will allow for formation of a mirage." (CR p. 625)
That leads to the next point:
3. The UFO's initially were apparently too far below the horizon to have been mirages. Capt Howard states there were stratocumulus clouds at 14,000 feet which were left behind as the sighting unfolded:
"They were moving at about the same speed
as we were
This gives us an estimated 30 to 45-degree depression angle for the UFO's, or using McDonald's reported distance figures (5-6 miles) a depression angle of about 20-25 degrees. This is orders of magnitude beyond the maximum grazing angle for a mirage (less than 1/2 deg).
4. Capt Howard's observation that the UFO's seemed to "climb" to nearly the BOAC's altitude would seem to suggest the objects moved ABOVE the apparent horizon of the earth. This would be an extraordinary and perhaps unprecedented event in the history of atmospheric optics to have an "inferior mirage" (one appearing below the horizon) smoothly transition into a "superior mirage" (one appearing above horizon) without radical distortion or abrupt disappearance between those phases.
Temperature inversions cause superior mirages ("superrefractive" conditions). Inferior mirages are caused by the _opposite_ of inversion conditions, where the temperature _drops_ instead of increases and drops with height at faster than normal lapse rates ("subrefractive" conditions). (CR pp. 625, 689-690)
4. Though the UFO's seemed to "pace" the BOAC airliner at the same relative direction throughout the sighting, in actuality they seemed to stay with the descending sun low over the horizon, which itself changed direction by about 5-7 degrees with respect to the airliner's course, i.e., moved to the right or north in direction. If the UFO's had strictly stayed at exactly the same relative direction from the BOAC cruiser (about 300 degs true) then their separation angle from the sun of about 5 degrees would have doubled to about 10-12 degrees which might have been quite noticeable to the BOAC crew, but was evidently not.
5. Thayer suggested the "slim possibility" that the wake of the airliner itself may have intensified a barely subcritical layer enough to create a mirage condition which would then follow the airliner at the same relative direction. Of course no one has obtained meteorological data for the time, date and location showing any conditions for mirage formation at all, let alone a conveniently just subcritical layer. The UFO direction was indeed behind and to the side of the airliner where one would expect the wake. (Depending on the aircraft heading, about 90-110 degs behind the aircraft.)
But to reiterate once again mirages are images of _some thing_ not images of air. Either the mirage layer is off at extreme distance towards the earth's horizon about 250 miles away from the airliner or it is a relatively close layer at the airliner's 19,000 foot altitude. If it is a close layer it can only refract an image of _something_ within a half degree elevation angle from the layer, i.e., essentially at the same 19,000-foot altitude. What else was up there at that height and close enough to be seen but the UFO's? Only dark clouds are a possibility and a coincidental series of mirages of dark clouds at exactly the right distance and angle from the BOAC liner as to seem _continuous_ for some 20 minutes would be an impossibility. It is also contradicted by Capt Howard's obseravtion that they left the only clouds behind them as they crossed overland into Labrador and from there it was "sky clear, visibility unlimited."
6. Normally one expects mirages of the _sun_ might behave like a jelly, as the black objects were reported here to do, because there is then plenty of light to see refractive oddities, and globs of yellow-red sunlight might be seen shimmering and merging. But in this case it wasn't the setting sun itself that was miraged but black or dark objects that were seen -- in effect the exact opposite of bright sun. The sun was far from actually setting, being 3-7 degrees above the apparent horizon, which makes it difficult to account for sunlight refracting and screening or shadowing clouds against other clouds or haze, since it is far above the critical grazing angle for mirages (less than 1/2 deg). Also, one would expect some sort of sub-sun effect to be directly below the sun, not off at an angle to the left (see 20-minute aircraft sighting and photo Case 54 in Condon Report pp. 457-463).
The UFO's here were not described as metallic vehicles. I have found no angular size data so far, so it's not possible to be sure how close a look the BOAC crew and passengers got. The only remote or "slim possibility" of explanation seems to be a mirage as Loren suggested but it is contradicted by physics data indicating a virtual impossibility.