halo (redirected from senile halo)

halo, in meteorology

halo, in meteorology, short-lived circles or arcs, and less commonly spikes and crosses, of colored or whitish light surrounding the moon or sun or in clouds as seen from above. A halo occurs when the light from the sun or the moon is refracted and reflected by ice crystals in the atmosphere, usually in a thin layer of high cirrostratus clouds. Under certain circumstances a second, or outer, halo appears, which is fainter than the inner one. At times white or colored luminous arcs are also seen lying somewhat parallel to the horizon and passing through the source of light, called mock suns, parhelia, or sun dogs for the sun, and paraselenae for the moon. A single mock sun, the anthelion, directly opposite the sun, may be added. In general a white halo results from the reflection of light by ice crystals, while one which appears as colored rings results from the refraction of light by ice crystals. Halos are more brilliant and complex near the poles than in other parts of the world. The theory attributing their formation to the presence of ice crystals was first suggested by the 17th cent. French philosopher Descartes. Similar to a halo and sometimes confused with it is the sun's corona. In X-ray electron diffraction, the term halos refers to the broad rings that appear on a photographic film as a result of the diffraction of a monoenergetic beam of X rays or electrons from a crystalline powder located at the center of the camera.

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halo, in art

halo, in art: see nimbus.

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halo

1. a disc or ring of light around the head of an angel, saint, etc., as in painting or sculpture

2. a circle of light around the sun or moon, caused by the refraction of light by particles of ice

3. Astronomy a spherical cloud of stars surrounding the Galaxy and other spiral galaxies

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halo [′hā·lō]

(astronomy)

A type of ray system in which many short, filamentary streaks form a complex network of bright matter surrounding the lunar crater. Also known as nimbus.

(electronics)

An undesirable bright or dark ring surronding an image on the fluorescent screen of a television cathode-ray tube; generally due to overloading or maladjustment of the camera tube.

(geology)

A ring or crescent surrounding an area of opposite sign; it is a diffusion of a high concentration of the sought mineral into surrounding ground or rock; it is encountered in mineral prospecting and in magnetic and geochemical surveys.

(meteorology)

Any one of a large class of atmospheric optical phenomena which appear as colored or whitish rings and arcs about the sun or moon when seen through an ice crystal cloud or in a sky filled with falling ice crystals.

(optics)

A ring around the photographic image of a bright source caused by light scattering in any one of a number of possible ways.