Project Blue Book case file: Kenneth Arnold

Read from the scan by GLM-OCR; expect the odd misread word.

incident #17 -- page 2

must have been erroneous:

that the objects seemed about 20 times as long as wide. Let us assume that the thickness was just discernible, which means that the object was just at the limit of resolution of the eye. Now, the eye cannot resolve objects that subtend an angle of appreciably less than 3 minutes of arc, and, in general, for any detail to be seen at all, the angle subtended must be much greater. Even if we assume the limiting resolution of 3 minutes, then, if the distance was 25 miles, elementary calculations show that each object must have been at least 100 feet thick, and if, as drawings indicate, the object was some 20 times longer than wide, it must have been about 2000 feet long.

Looking at the matter in another way and assuming that estimate of distance as 20 to 20 miles (120,000 feet) and his estimate of length as 40 to 50 feet are both correct, then it can be shown that the object will subtend an angle of only about 80 seconds of arc, which is definitely below the limit of resolution of the eye.

If I actually saw the objects, and if his estimate of distance is correct, that of size cannot be, and vice versa. It seems most logical to assume that his estimate of distance is far too great. In fact, assuming a reasonable limiting size to the objects of 400 feet, in order to show the detail that drawings indicate, the distance must have been not over roughly six miles. At this distance the objects would have travelled 11 miles (rather than 47 miles) in 102 seconds, or at a rate of approximately 400 m.p.h.