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A sunbeam, in
meteorological optics Atmospheric optics is "the study of the optical characteristics of the atmosphere or products of atmospheric processes .... ncludingtemporal and spatial resolutions beyond those discernible with the naked eye". Meteorological optics is "that par ...
, is a
beam Beam may refer to: Streams of particles or energy *Light beam, or beam of light, a directional projection of light energy **Laser beam *Particle beam, a stream of charged or neutral particles **Charged particle beam, a spatially localized grou ...
of
sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
that appears to radiate from the position of the Sun. Shining through openings in clouds or between other objects such as mountains and buildings, these beams of particle-scattered sunlight are essentially
parallel Parallel is a geometric term of location which may refer to: Computing * Parallel algorithm * Parallel computing * Parallel metaheuristic * Parallel (software), a UNIX utility for running programs in parallel * Parallel Sysplex, a cluster of IBM ...
shafts separated by darker
shadow A shadow is a dark area where light from a light source is blocked by an opaque object. It occupies all of the three-dimensional volume behind an object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, o ...
ed volumes. Their apparent convergence in the sky is a visual illusion from linear perspective. The same illusion causes the apparent convergence of parallel lines on a long straight road or hallway at a distant vanishing point. The scattering particles that make sunlight visible may be air molecules or
particulates Particulates – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter (PM) or suspended particulate matter (SPM) – are microscopic particles of solid or liquid matter suspended in the air. The ter ...
.


Crepuscular rays

'' Crepuscular rays'' or ''god rays'' are sunbeams that originate when the sun is just below the horizon, during
twilight Twilight is light produced by sunlight scattering in the upper atmosphere, when the Sun is below the horizon, which illuminates the lower atmosphere and the Earth's surface. The word twilight can also refer to the periods of time when this il ...
hours. Crepuscular rays are noticeable when the contrast between light and dark is most obvious. Crepuscular comes from the Latin word "crepusculum", meaning twilight. Crepuscular rays usually appear orange because the path through the atmosphere at sunrise and sunset passes through up to 40 times as much air as rays from a high midday sun. Particles in the air scatter short wavelength light (blue and green) through Rayleigh scattering much more strongly than longer wavelength yellow and red light. Loosely, the term "crepuscular rays" is sometimes extended to the general phenomenon of rays of sunlight that appear to converge at a point in the sky, irrespective of time of day.


Antisolar rays

In some cases, sunbeams may extend across the sky and appear to converge at the antisolar point, the point on the
celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...
opposite of the Sun's direction. In this case, they are called ''antisolar rays'' (anytime not during astronomical night) or '' anticrepuscular rays'' (during the
twilight Twilight is light produced by sunlight scattering in the upper atmosphere, when the Sun is below the horizon, which illuminates the lower atmosphere and the Earth's surface. The word twilight can also refer to the periods of time when this il ...
period). This apparent dual convergence (at both the solar and the antisolar points) is a perspective effect analogous to the apparent dual convergence of the parallel lines of a long straight road or hallway at directly opposite points (to an observer above the ground).


Alternative names

* Backstays of the sun, a nautical term, from the fact that backstays that brace the mast of a sailing ship converge in a similar way * Buddha rays * God rays, used by some members of the computer graphics industryE.g. this term is mentioned in: * Jacob's Ladder * Light shafts, sometimes used in the computer graphics industry, such as the game engine
Unreal Engine Unreal Engine (UE) is a 3D computer graphics game engine developed by Epic Games, first showcased in the 1998 first-person shooter game ''Unreal''. Initially developed for PC first-person shooters, it has since been used in a variety of genres ...
* Ropes of Maui, originally ''taura a Maui''—from the Maori tale of Maui Potiki restraining the sun with ropes to make the days longer * Sun drawing water, from the
ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
belief that sunbeams drew water into the sky (an early description of
evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when humidi ...
)


See also

* * * * * * * *


References


External links

{{commons and category
Sunrays - Crepuscular rays, Explanation & Images


Atmospheric optical phenomena Sun