Sunbeam

Crepuscular rays

Main article: Crepuscular rays

Crepuscular rays or god rays are sunbeams that originate when the sun is just below the horizon, during twilight 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.

Anticrepuscular rays

Main article: Anticrepuscular rays

In some cases, sunbeams may extend across the sky and appear to converge at the antisolar point, the point on 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 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 industry
• Jacob's Ladder
• Light shafts, sometimes used in the computer graphics industry, such as the game engine Unreal Engine
• Ropes of Maui, originally taura a Mauifrom the Maori tale of Maui Potiki restraining the sun with ropes to make the days longer
• Sun drawing water, from the ancient Greek belief that sunbeams drew water into the sky (an early description of evaporation)

References

References

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6. "Weather Facts: Crepuscular rays | weatheronline.co.uk".
7. Cowley, Les. "Anti-solar (anti-crepuscular) rays". Atmospheric Optics.
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11. "Light Shafts".