Condign volumes 1 to 3

# UNCLASSIFIED

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perceived and reported as flying much lower than they actually are.

## THE ILLUSION OF OBJECT MOTION

18. It is important to note that (other types of actual flying objects excepted), with those visual phenomena which are due to certain atmospheric effects, little of substantial physical substance actually moves. It is the light seen by the observer that moves from place to place and it becomes visible in those places because the atmospheric conditions (electrical, particle etc.), allow it to become visible. Hence, the observed variation in colours seen, the duration for which an object is seen, and the time for which a sightline rate is discernible. The visualisation (wavelength) of a UAP, from an electrical charge source, also depends upon air pressure.

## VELOCITY ILLUSION

19. The illusion of velocity in receding objects is particularly important in UAP reports, where, as they are often in the dark, leave the observer with no surface references with which to relate speed. This is especially the case when the sky background does not offer a simultaneous view of any aircraft, with which to compare sightline motion. Similarly, in bright sunlight the velocity of a small receding spherical object is particularly difficult to assess. This is dependent on whether the object being viewed is just a spherical (i.e. 'round') light, (which may be bright or dim) or whether it is being viewed as a silhouette. The surface area of a receding sphere is seen purely as the area of a circle $ \left( \Pi r^{2} \right) $ and the enclosed angle resulting (i.e.subtended) from its diameter, as range increases, will reduce linearly as the ratio of its diameter to range. However, its area appears to the observer to have shrunk according to the square law. The important feature here is that a sphere comprising plasma, which might not be accelerating away (or even be moving away at linear speed) but is in fact shrinking in size (as its, often brief, lifetime comes to an end as the electrical forces holding it stable collapse), can

appear, from the observer's viewpoint, to be receding; whereas, it is actually an illusion and the object may hardly have moved in range.

It is easily seen, therefore, that a reported 'receding light', may in fact be a light which is reducing in intensity but remaining in exactly the same spot. Similarly a 'rotating' light may be a fluctuating light, which is the same light giving the impression of rotation.