The weather bureau records for that evening, obtained from radiosonde observations, show that temperature inversions existed both near the ground and at higher altitude. Thus conditions were ideal to produce a furiously twinkling planetary mirage. When a planet is close to the horizon this twinkling, together with the defocusing action of the earth’s atmosphere, can spread out the image so that it looks huge, with an apparent diameter as great as ten minutes of arc. Under such conditions, both the size and the intensity of the light fluctuate. When they diminish, the object seems to be racing away from the observer; when they increase, it seems to be rushing directly towards him on a collision course. The peculiar lens-like action of the atmosphere makes the image seem to be, not at infinity, but only a few hundred feet away from the observer.
Seen through the distorting atmospheric lens, the image of Jupiter could have performed exactly as Gorman described: it would have darted back and forth, seemed to attack, retreat, and carry out the “controlled” maneuvers that actually depended partly on the movement of the plane itself. Gorman apparently assumed that he was dealing with a material object (as indeed he was in the beginning), and therefore did not consider the possibility that he was seeing merely an optical image.
The geographical situation would have helped produce the illusion. Fargo lies at an elevation of about 900 feet and the land rises gradually to the west. Due west is Bismarck at 1670 feet. To the south lies a series of buttes, some of them as high as 3500 feet. Thus in the southwest where Jupiter was setting and where the UFO attacked from, the buttes would repeatedly have cut off the planet from view as Gorman maneuvered, so that the image would have seemed to race in and out and perform evasive actions, just as did the mirage of Sirius in Alaska ([p. 60]). Since Jupiter was very low, however, the buttes served to conceal it from the observers on the ground.
Figure 9. Positions of refracted image of Jupiter from 9:00 to 9:29 P.M. at Fargo, North Dakota, on October 1, 1948. Azimuth measured north through east.
The times involved provide the last piece of the puzzle. The dogfight ended at about 9:27. The time of the geometrical setting of Jupiter was 9:25. The usual lag due to refraction is between two and three minutes (see [Figure 9]). The planet therefore remained visible for about two minutes longer. The image actually sank below the horizon and disappeared from view between 9:27 and 9:28, the same time that the UFO climbed straight up into the sky and disappeared. When Jupiter vanished, the unknown also vanished and did not return.
Absolute proof of this solution is of course impossible. Nevertheless, the description of the UFO, its behavior, its direction, its time of disappearance—all are consistent with its identification as Jupiter. The Gorman case might reasonably be removed from the “Balloon?” category and listed as “Balloon plus planetary mirage.”
Jupiter through a Jet Trail
Venus, Mars, and Jupiter seen under unusual conditions can mystify even the most hardheaded witness. Unrecognized air turbulence and increased scattering of the light can easily create the illusion of a flying saucer.
An ex-army man, a trained observer with a good knowledge of physics and optics, reports the following unnerving experience[[IV-11]].