Condign volumes 1 to 3

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

# UNCLASSIFIED UK RESTRICTED

angle) is said to be $ 2 2^{\circ} $ . Halos from the sun can be either above or below the horizon. Halo activity is persistent and is known to many of the public, however it results in some UAP reports. Over a 40 year period (Netherlands) it was noted that average halo conditions existed for 227 days of the year, peaking in 1972, when 300 days were recorded.

13. On other days conditions existed for other parhelian and circumzenithal events. Halo Arcs occur at low solar elevations and are caused by pyramidal crystals and occur when they fall through the air with certain axes vertically orientated. Halo rings of unusual radii can be produced when their faces are not in random orientation. From those in random orientation six concentric odd-radii halos should result at 9, 18.3, 19.9, 22.9, and 23.8 degrees. Each of these six halo types has been imaged this century, but most of the 12 (yet undiscovered) forms are, at most solar elevations, completely below the horizon and thus only visible from airborne platforms in cool climates. The 12 halos divide into 32 individual arcs in the sky, of which only ten, so far, have been photographed. Halos still escape a complete understanding. In particular, ice particles with pyramidal ends are suspected of producing bright arcs of dimension of odd radius halos. It should be noted that some effects can be related to the polarisation of observers' sun-glasses!

Although the photograph at Figure 13 is artificially produced by light passing through a single vertically orientated hexagonal ice crystal (the parhelic spots shown are the actual projection on a wall), it is noted that these shapes are markedly similar to some UAP reports where 'multiple balls' are described.

## SUN DOGS

14. A 'sun dog' (parhelian) is a mock sun, a parhalion. (See also para.20 and Figure 14)

## St. ELMO's FIRE

15. This is commonly mis-identified as ball (or bead) lighting. It has been reported for thousands of years and is a corona discharge from a 'grounded' point in a strong electric field, hence, it is usually observed as a glowing object hovering over an earthed object before or during a thunderstorm. It is commonly blue or blue-white in appearance and about the size of a large orange. However, much larger diameters - up to 30cm - have been seen. It decays silently, sometimes slowly and sometimes suddenly, with a lifetime of (usually) many seconds, which may extend to minutes. A characteristic distinction between St. Elmo's Fire and Ball/Bead lighting is that the latter has motion. The exception is when St. Elmo's Fire moves along a conductor.

## BIRDS

15. Small flocks of birds (e.g. gulls) can be reported at night as UAPs. Their reflective under-bellies can be seen in triangular formation. Because no sound may be heard this increases the likelihood of an unwary observer, who may only see the birds for a few seconds as they wheel; producing a brief visual reflection. In bright sunlight seagulls have high reflectivity. The specular reflection from the body reported as 'bluish white' observes the fact that it is a bird as the bright flash obscures the wings. Clusters of sightings tend to occur in areas of 'greatest watchfulness' - for example near airfields and population centres. The radar echoing area (i.e. RCS) of birds is