Sundogs are another special effect resulting from a peculiar combination of circumstances, and they continue to supply their quota of good UFO reports. Tiny ice crystals floating in a layer of quiet air and reflecting a bright sun are responsible for producing sundogs. A thin layer of such crystals may be invisible to the observer; a thick layer appears as the familiar cirrus clouds. Sunlight filtering through such an ice fog is reflected in each crystal so that a pattern of bright spots of light forms in the sky, an image of the sun that sometimes rivals the sun itself in brilliance. These images are called mock suns, sundogs, or parhelia when they accompany the sun (and mock moons, moondogs, or paraselenae when they accompany the moon). They appear in the sky at a position a given distance from the sun and usually have a trace of red on the edge nearest the sun. Occasionally a sundog makes a complete circle of light surrounding the sun with four bright patches, one above, one below, and one on either side. Sometimes two circles will appear, one within the other, surmounted by an inverted arc and traversed by a cross, like the spokes of a wheel whose center is the sun. The complicated structure of a fully developed mock sun--which is extremely rare--can suggest to the imaginative an enormous chariot in the sky and can terrify the superstitious. There is little doubt that this phenomenon inspired the two visions of Ezekiel described in the Bible. Mock suns have been the cause of many UFO sightings. Even after several publications [see [XII-1a]] explained how the sun reflected from ice crystals could account for some of the reported flying saucers, this idea was largely ignored by early investigators who had a limited training in the physical sciences. Sundogs are relatively uncommon. Few airmen, even those with long experience, have learned to recognize them. In a poll of both commercial and military pilots, Dr. Menzel found that only one in five knew what a sundog was and how it might look in the sky. Two of three generals in the Air Force, similarly, were unfamiliar with the phenomenon. Like balloons, sundogs have a silvery metallic sheen. When observed from the ground, they seem to hover or move very sluggishly; to a witness in the air they seem to move rapidly, to pace the plane, or to take evasive action as though under intelligent control. When enough data are available, and the time of day and the position of the unknown relative to the sun are appropriate, a mock sun should be considered as a possible explanation of the UFO.