Office of the Secretary of Defense: 016_Parallax_Paper

All-domain Anomaly Resolution Office (AARO)
person is between five and six feet tall. In this example, forced perspective distorts the distance
between the tower and the person, causing both the person to appear larger and the tower to
appear smaller than their true sizes.
The example above demonstrates the effects of forced perspective. Recognizing the optical
illusion in this case is easy because the actual sizes of both objects in the image are known.
However, judging the sizes of unknown objects in the sky is harder. Observers will often
compare unknown objects to clouds, trees, buildings, or other non-standard references to make
estimates. Observers can, therefore, inaccurately perceive the distance between an object and a
reference, leading to an inaccurate estimate of the object’s actual size. Making an error while
estimating an object’s size or distance is even more likely if, unlike the Tower of Pisa, the object
has no discernable features (e.g., windows, propellers, wings).
Consider a case in which there are no references against which to compare an unknown object.
In such a case, an observer must estimate its distance without any clues. Accurately estimating an
object’s size and distance without a known reference is difficult. Forced perspective can cause
large, faraway objects to appear smaller and closer than their actual size and position - or vice
versa. The image in Figure 2 demonstrates this effect. A 10’ sphere with no features (e.g.,
windows, lines, surface details) positioned at an unknown distance from an observer may appear
smaller or larger than its actual size, depending on the observer’s reference point and
assumptions.
Figure 2: The 10’ sphere on the far right is an unknown distance from the observer. If the
observer estimates the range to be shorter, they will estimate the size to be smaller.016
Page determined to be Unclassified
Reviewed by Chief of Staff, AARO
IAW FY24 NDAA, Section 1841(a)(1)(C)
Date: 2/6/2025