Anthelia

Anthelia (Gr. anti, 'opposite,' and hēlios, 'the sun'), or GLORIES, are luminous rings seen by an observer on a cloud or fog which lies opposite to the sun. They occur chiefly in alpine regions and in the polar seas, and are only seen when sunshine and cloud, or fog, occur at the same time. They appear in the following way: When, from an elevated position—as the mast of a ship, or the ridge of a hill—the shadow of an observer is projected by the sun on a cloud or fog, he sees the head encircled by a glory or luminous ring, diminishing in brightness as it leaves the head as a centre. When the sun shines brightly, and the fog is dense, as many as four concentric rings of this nature are seen by the observer round the shadow of his head, having their common centre in the point where a line from the sun through the eye of the observer meets the fog. When the phenomenon assumes this form, the rings are more or less coloured—the colours of the two inner rings being generally brilliant, those of the third more faint, while those of the fourth are scarcely perceptible. This last has an angular radius of about 40°, and is very seldom seen. It bears frequently the name of the Circle of Uloa or the White Rainbow. A phenomenon substantially similar to the anthelia occurs when, the sun being near the horizon, the observer sees an anreola surrounding the shadow of his head cast upon grass or corn moistened with dew. See HALOS, DIFFRACTION, LIGHT, RAINBOW, REFRACTION.