Investigators from ATIC arrived promptly but they were not able to explain the sighting. Even the photographs showed nothing useful. Conclusion: unknown.
The incident remained unexplained chiefly because the investigators, like the witnesses, apparently assumed that a single unidentified flying object accounted for all the phenomena observed that evening. Although the available evidence is somewhat confusing, a careful study shows that, on the contrary, the visual and the radar targets could not have been the same.
When the ground spotter first reported the UFO, she described it as a stationary light low on the horizon. The radarscope, however, showed a target that was moving slowly, at an altitude of about 16,000 feet. Some minutes later, when the visual target did begin to move, the radar target speeded up. This was the only instance in which the movements of the two seemed to be roughly parallel. But in the excitement that followed, all the witnesses assumed that the two targets were identical. The published account[[VIII-3], p. 303 ff.] does not distinguish clearly between the actions of the light and the movements of the blips on the radarscope.
Let us begin by reviewing the facts about the visual target. According to the witnesses on the ground, it was a brilliant bluish-white light that appeared on the northeast horizon and remained stationary during most of the period it was observed. At one time it seemed to advance rapidly toward the witnesses, make a wide sweep around Rapid City, which was a few miles away from the observers, and then return to its original position. According to the witnesses in the air, the light did not remain stationary but retreated from the pursuing plane and followed the returning plane, duplicating the plane’s speed and keeping the distance between them constant. The pilots based this interpretation, evidently, on the fact that the light did not vary in size or brilliance and thus seemed to pace the plane.
These descriptions all point to the same answer: that the light was a star or a planet. Since it was infinitely distant, the jets could not get any closer to it and at ground levels the image was distorted by peculiar atmospheric conditions. Mars had been absent from the night sky for months, and Mercury, Venus, and Jupiter were then morning stars; therefore the unknown could not have been a planet. However, the bright star Capella was on the northeast horizon at a declination of plus 46 degrees and would have been visible from both Fargo and Rapid City. A check of the Weather Bureau records shows that the night was clear and dark. The sun had set about an hour before the sighting began, and at that time in the evening there was no moonlight because the moon was in its last quarter. Visibility was about thirty-five miles and the wind was from the northeast, about four meters per second. There was a marked temperature inversion—9 degrees—at ground levels. Such an inversion could easily account for the erratic motions reported for the light.
There can be little doubt that the visual target was the star Capella.
The radar targets also were clearly the result of weather, just as the air-traffic controller had suspected when he first looked at the scope. Conditions were ideal—a calm, clear, warm summer night—for phantom echoes. The first radar target, moving southwest, was probably a return from some ground object. When the jet took to the air, the scope showed a different kind of UFO target, one that echoed the movements of the plane itself—retreating from the pursuer, advancing when the pursuer turned back—and was always farther away from the ground station than the plane itself.
Although saucer enthusiasts interpret these maneuvers as proof that the phantom was under intelligent control, radar experts recognize the familiar pattern in which a ghost echo is actually a return from the plane itself. Because of the temperature inversions the radar pulses do not return directly from the plane to the ground receiver but are deflected from the plane to the ground, then back to the plane, and thence on to the ground scope. The phantom echo always occurs from the same direction as the aircraft and is always “on the other side” of the plane (see [p. 153]).
This explanation also accounts for the evidence of the jet’s gun camera. The photographs taken showed nothing, although the radar warning light indicated a solid object ahead. After the pilot had switched on the set, however, there had been a brief delay before the red signal blinked on. During this interval the plane had not come any closer to the unknown light, but the radio waves had scattered from plane to ground and back to plane so that the gun radar did indeed detect a solid object—the plane itself!
In short, the evidence supports our conclusion that an image of the star Capella, distorted by the atmospheric conditions produced by a strong temperature inversion, accounted for the visual sightings; and that radar echoes from the pursuing jets, deflected by the same temperature inversion, accounted for the phantom targets on the ground radarscope and the gun radar.