Crepuscular rays, sometimes colloquially referred to as god rays, are
sunbeam
A sunbeam, in meteorological optics, is a lightbeam, beam of sunlight 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 light scatter ...
s that originate when the
Sun
The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
appears to be just above or below a layer of clouds, during the
twilight
Twilight is daylight illumination produced by diffuse sky radiation when the Sun is below the horizon as sunlight from the upper atmosphere is scattered in a way that illuminates both the Earth's lower atmosphere and also the Earth's surf ...
period.
Crepuscular
In zoology, a crepuscular animal is one that is active primarily during the twilight period, being matutinal (active during dawn), vespertine (biology), vespertine/vespertinal (active during dusk), or both. This is distinguished from diurnalit ...
rays are noticeable when the
contrast between light and dark is most obvious. Crepuscular comes from the Latin word , meaning "twilight". Crepuscular rays usually appear orange because
the path through the atmosphere at
dawn
Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the diffuse sky radiation, appearance of indirect sunlight being Rayleigh scattering, scattered in Earth's atmosphere, when the centre of the Sun's disc ha ...
and
dusk
Dusk occurs at the darkest stage of twilight, or at the very end of astronomical twilight after sunset and just before nightfall.''The Random House College Dictionary'', "dusk". At predusk, during early to intermediate stages of twilight, enoug ...
passes through up to 40 times as much air as rays from a high Sun at
noon
Noon (also known as noontime or midday) is 12 o'clock in the daytime. It is written as 12 noon, 12:00 m. (for '' meridiem'', literally 12:00 midday), 12 p.m. (for ''post meridiem'', literally "after midday"), 12 pm, or 12:00 (using a 24-hour cl ...
.
Particles in the air scatter short-
wavelength
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats.
In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
light (blue and green) through
Rayleigh scattering
Rayleigh scattering ( ) is the scattering or deflection of light, or other electromagnetic radiation, by particles with a size much smaller than the wavelength of the radiation. For light frequencies well below the resonance frequency of the scat ...
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
Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible spectrum, visible light perceptible to the human eye as well as invisible infrare ...
that appear to converge at a point in the sky, irrespective of time of day.
A rare related phenomenon are
anticrepuscular rays which can appear at the same time (and coloration) as crepuscular rays but in the opposite direction of the setting sun (east rather than west).
Gallery
File:Crepuscular Rays, India - NASA Earth Observatory.jpg, Orbital view of crepuscular rays
File:heron-island-sunset.jpg, Sunset at Heron Island, Queensland, Australia (April 2023)
File:Сончеви зраци над Тиквеш (cropped).jpg, Crepuscular rays before sunset, Tikveš
See also
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References
External links
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Atmospheric optical phenomena
Sun
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