Crepuscular rays
Encyclopedia
Crepuscular rays in atmospheric
optics
, are rays
of sunlight
that appear to radiate from a single point in the sky. These rays, which stream through gaps in clouds (particularly stratocumulus) or between other objects, are columns of sunlit air separated by darker cloud-shadowed regions. The name comes from their frequent occurrences during crepuscular
hours (those around dawn and dusk), when the contrasts between light and dark are the most obvious. Crepuscular comes from the Latin
word crepusculum meaning twilight.
. Various airborne compounds scatter the sunlight and make these rays visible, due to diffraction
, reflection, and scattering.
Crepuscular rays can also occasionally be viewed underwater, particularly in arctic areas, appearing from ice shelves or cracks in the ice.
There are three primary forms of crepuscular rays:
They are commonly seen near sunrise and sunset, when tall clouds such as cumulonimbus and mountains can be most effective at creating these rays.
are generated in the same way. The rays in some cases may extend across the sky and appear to converge at the antisolar point
, which is the point on the sky sphere directly opposite the sun, and they are called anticrepuscular rays. Like crepuscular rays, they are parallel shafts of sunlight from holes in the clouds, and their apparent convergence is a perspective effect. They are not as easily spotted as crepuscular rays.
much more strongly than longer wavelength yellow and red light.
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
, are rays
Ray (optics)
In optics, a ray is an idealized narrow beam of light. Rays are used to model the propagation of light through an optical system, by dividing the real light field up into discrete rays that can be computationally propagated through the system by the techniques of ray tracing. This allows even very...
of sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
that appear to radiate from a single point in the sky. These rays, which stream through gaps in clouds (particularly stratocumulus) or between other objects, are columns of sunlit air separated by darker cloud-shadowed regions. The name comes from their frequent occurrences during crepuscular
Crepuscular
Crepuscular animals are those that are active primarily during twilight, that is during dawn and dusk. The word is derived from the Latin word crepusculum, meaning "twilight." Crepuscular is, thus, in contrast with diurnal and nocturnal behavior. Crepuscular animals may also be active on a bright...
hours (those around dawn and dusk), when the contrasts between light and dark are the most obvious. Crepuscular comes from the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
word crepusculum meaning twilight.
Appearance
Crepuscular rays are near-parallel, but appear to diverge because of linear perspective. They often occur when objects such as mountain peaks or clouds partially shadow the sun's rays like a cloud coverCloud cover
Cloud cover refers to the fraction of the sky obscured by clouds when observed from a particular location...
. Various airborne compounds scatter the sunlight and make these rays visible, due to diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
, reflection, and scattering.
Crepuscular rays can also occasionally be viewed underwater, particularly in arctic areas, appearing from ice shelves or cracks in the ice.
There are three primary forms of crepuscular rays:
- Rays of light penetrating holes in low clouds (also called "Jacob's LadderJacob's LadderJacob's Ladder is a "ladder to heaven", described by biblical Jacob in the Book of GenesisJacob's Ladder may also refer to:* Ladder of Jacob, a pseudepigraphic text of the Old Testament...
"). - Beams of light diverging from behind a cloud.
- Pale, pinkish or reddish rays that radiate from below the horizonHorizonThe horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...
. These are often mistaken for light pillarLight pillarA light pillar is a visual phenomenon created by the reflection of light from ice crystals with near horizontal parallel planar surfaces. The light can come from the Sun in which case the phenomenon is called a sun pillar or solar pillar...
s.
They are commonly seen near sunrise and sunset, when tall clouds such as cumulonimbus and mountains can be most effective at creating these rays.
Anticrepuscular rays
Crepuscular and anticrepuscular raysAnticrepuscular rays
Anticrepuscular rays are similar to crepuscular rays, but seen opposite the sun in the sky. Anticrepuscular rays are near-parallel, but appear to converge at the antisolar point because of linear perspective. Anticrepuscular rays are most frequently visible near sunrise or sunset. Crepuscular rays...
are generated in the same way. The rays in some cases may extend across the sky and appear to converge at the antisolar point
Antisolar point
The antisolar point is the imaginary point on the celestial sphere exactly opposite the Sun. It is where anticrepuscular rays appear to converge, and on a moonless night away from city lights, it is often possible to see the gegenschein there. The apex of a rainbow will also form roughly 42...
, which is the point on the sky sphere directly opposite the sun, and they are called anticrepuscular rays. Like crepuscular rays, they are parallel shafts of sunlight from holes in the clouds, and their apparent convergence is a perspective effect. They are not as easily spotted as crepuscular rays.
Color
Crepuscular rays are usually red or yellow in appearance because the path through the atmosphere at sunrise and sunset pass 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 scatteringRayleigh scattering
Rayleigh scattering, named after the British physicist Lord Rayleigh, is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. The particles may be individual atoms or molecules. It can occur when light travels through...
much more strongly than longer wavelength yellow and red light.
Alternative names
- Sunbeams
- SunburstSunburstSunburst is a type of finish for musical instruments such as electric and acoustic guitars and electric basses. At the center of a sunburst-finished surface is an area of lighter color that darkens gradually towards the edges before hitting a dark rim...
- Sun rays
- Sun drawing water - from the ancient GreekAncient GreeceAncient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...
belief that sunbeams drew water into the sky (an early description of evaporationEvaporationEvaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....
) - Backstays of the sun - a nautical term, from the fact that backstayBackstayOn a sailing vessel, a backstay is the piece of standing rigging that runs from the mast to the transom of the boat, counteracting the forestay and jib...
s that brace the mast of a sailing ship converge in a similar way - Ropes of Maui - (originally. taura a Maui) from the Maori tale of Maui Potiki restraining the sun with ropes to make the days longer
- Jacob's LadderJacob's LadderJacob's Ladder is a "ladder to heaven", described by biblical Jacob in the Book of GenesisJacob's Ladder may also refer to:* Ladder of Jacob, a pseudepigraphic text of the Old Testament...
- Gateways to Heaven, Stairways to Heaven and Paths to Heaven
- God Rays, Fingers of GodFingers of GodFingers of God is an effect in observational cosmology that causes clusters of galaxies to be elongated in redshift space, with an axis of elongation pointed toward the observer. It is caused by a Doppler shift associated with the peculiar velocities of galaxies in a cluster...
(or God's Fingers), so called because they appear often in the background on religious pictures. - Jesus Beams, Beams of Jesus, or Jesus Rays
- Cloud breaks
- Volumetric lightingVolumetric lightingVolumetric lighting is a technique used in 3D computer graphics to add lighting effects to a rendered scene. It allows the viewer to see beams of light shining through the environment; seeing sunbeams streaming through an open window is an example of volumetric lighting, also known as crepuscular...
(used by the computer graphics industry) - Buddha's Rays
- Divine Light
- Scott's Rays
See also
- AirglowAirglowAirglow is the very weak emission of light by a planetary atmosphere. In the case of Earth's atmosphere, this optical phenomenon causes the night sky to never be completely dark .-Development:The airglow phenomenon was first identified in 1868 by Swedish scientist...
- Anticrepuscular raysAnticrepuscular raysAnticrepuscular rays are similar to crepuscular rays, but seen opposite the sun in the sky. Anticrepuscular rays are near-parallel, but appear to converge at the antisolar point because of linear perspective. Anticrepuscular rays are most frequently visible near sunrise or sunset. Crepuscular rays...
- Light beamLight beamA light beam or beam of light is a narrow projection of light energy radiating from a source into a beam. Sunlight is a natural example of a light beam when filtered through various mediums...
- Rayleigh scatteringRayleigh scatteringRayleigh scattering, named after the British physicist Lord Rayleigh, is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. The particles may be individual atoms or molecules. It can occur when light travels through...
- Tyndall effectTyndall effectThe Tyndall effect, also known as Tyndall scattering, is light scattering by particles in a colloid or particles in a fine suspension. It is named after the 19th century physicist John Tyndall. It is similar to Rayleigh scattering, in that the intensity of the scattered light depends on the fourth...