meteorology Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. It has applications in the military, aviation, energy production, transport, agricultur ...

, a corona (plural ''coronae'') is an

optical phenomenon Optical phenomena are any observable events that result from the interaction of light and matter. All optical phenomena coincide with quantum phenomena. Common optical phenomena are often due to the interaction of light from the Sun or Moon with ...

produced by the

diffraction Diffraction is the deviation of waves from straight-line propagation without any change in their energy due to an obstacle or through an aperture. The diffracting object or aperture effectively becomes a secondary source of the Wave propagation ...

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 ...

moonlight Moonlight consists of mostly sunlight (with little earthlight) reflected from the parts of the Moon's surface where the Sun's light strikes. History The ancient Greek philosopher Anaxagoras was aware that "''the sun provides the moon with its ...

(or, occasionally, bright

starlight Starlight is the light emitted by stars. It typically refers to visible electromagnetic radiation from stars other than the Sun, observable from Earth at night, although a component of starlight is observable from Earth during daytime. Sunlig ...

or planetlight) by individual small water droplets and sometimes tiny

ice crystals Ice crystals are solid water (known as ice) in crystal structure, symmetrical shapes including hexagonal crystal family, hexagonal columns, hexagonal plates, and dendrite (crystal), dendritic crystals. Ice crystals are responsible for various at ...

of a

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles, suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

or on a foggy glass surface. In its full form, a corona consists of several

concentric In geometry, two or more objects are said to be ''concentric'' when they share the same center. Any pair of (possibly unalike) objects with well-defined centers can be concentric, including circles, spheres, regular polygons, regular polyh ...

, pastel-colored rings around the

celestial object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists within the observable universe. In astronomy, the terms ''object'' and ''body'' are of ...

and a central bright area called an ''aureole''. The aureole is often (especially in case of the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

) the only visible part of the corona and has the appearance of a bluish-white disk which fades to reddish-brown towards the edge. The

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the ''visual an ...

of a corona depends on the

sizes Size in general is the Magnitude (mathematics), magnitude or dimensions of a thing. More specifically, ''geometrical size'' (or ''spatial size'') can refer to three geometrical measures: length, area, or volume. Length can be generalized ...

of the water droplets involved; smaller droplets produce larger coronae. For the same reason, the corona is the most pronounced when the size of the droplets is most uniform. Coronae differ from

halo HALO, halo, halos or haloes may refer to: Most common meanings * Halo (optical phenomenon) * Halo (religious iconography), a ring of light around the image of a head * ''Halo'' (franchise), a sci-fi video game series (2001–2021) Arts and en ...

s in that the latter are formed by

refraction In physics, refraction is the redirection of a wave as it passes from one transmission medium, medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commo ...

(rather than diffraction) from comparatively large rather than small ice crystals. The corona intensity pattern resembles an

Airy disk In optics, the Airy disk (or Airy disc) and Airy pattern are descriptions of the best-focus (optics), focused Point source#Light, spot of light that a perfect lens (optics), lens with a circular aperture can make, limited by the diffraction of ...

, since the diffraction pattern of a round obstacle is identical to that of a round aperture of the same diameter, except for the intensity of the undiffracted light, according to

Babinet's principle In physics, Babinet's principle states that the diffraction pattern from an opaque body is identical to that from an aperture (a hole in a screen) of the same size and shape except for the overall forward beam intensity. It was formulated in the ...

Pollen coronae

Pollen Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced Gametophyte#Heterospory, microgametophytes), which produce male gametes (sperm ...

suspended in the air can also cause diffraction of sunlight that produces coronae. Because pollen grains are not always spherical, the resulting pollen coronae often have characteristic elliptic shape and brighter spots in them. They can be seen during blooming season where there is significant source of pollen like forests. They are more easily seen during sunset or sunrise as there is less sun glare and the light path through pollen laden atmosphere is longer.

References

External links

Explanation and image gallery
- Atmospheric Optics by Les Cowley
Rings around the sun and moon: coronae and diffraction

Experimental simulations of pollen coronas

Gallery

File:Coronae.jpg, Forest Corona File:Coronae at GGB.jpg, Solar Corona at

Golden Gate Bridge The Golden Gate Bridge is a suspension bridge spanning the Golden Gate, the strait connecting San Francisco Bay and the Pacific Ocean in California, United States. The structure links San Francisco—the northern tip of the San Francisco Peni ...

File:Iridescent fog.jpg, Partial Corona at

File:Moon Marki 19032011 3.JPG, Lunar aureole File:Janus24.jpg, Lunar corona with Altocumulus floccus File:Lunar corona.JPG, Lunar aureole as seen from

Mumbai Mumbai ( ; ), also known as Bombay ( ; its official name until 1995), is the capital city of the Indian state of Maharashtra. Mumbai is the financial capital and the most populous city proper of India with an estimated population of 12 ...

File:SolarDiffractionCorona.jpg, A solar corona soon after

sunrise Sunrise (or sunup) is the moment when the upper rim of the Sun appears on the horizon in the morning, at the start of the Sun path. The term can also refer to the entire process of the solar disk crossing the horizon. Terminology Although the S ...

Atmospheric optical phenomena {{meteorology-stub

Pollen coronae

See also

References

External links

Gallery