meteorology Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...

, 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 wit ...

produced by the

diffraction Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...

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 ...

moonlight Moonlight consists of mostly sunlight (with little earthlight) reflected from the parts of the Moon's surface where the Sun's light strikes. Illumination The intensity of moonlight varies greatly depending on the lunar phase, but even the ful ...

(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. Sunligh ...

or planetlight) by individual small water

droplets A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the lower end of a tube or other surface boundary, producing a hanging drop called a pendant d ...

and sometimes tiny

ice crystals Ice crystals are solid ice exhibiting atomic ordering on various length scales and include hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust. Formation The hugely symmetric shapes are due to depositional growth, na ...

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 co ...

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, coaxal, or coaxial when they share the same center or axis. Circles, regular polygons and regular polyhedra, and spheres may be concentric to one another (sharing the same center point ...

, pastel-colored rings around the

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

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

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

) 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 distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it is ...

of a corona depends on the

sizes Size in general is the magnitude or dimensions of a thing. More specifically, ''geometrical size'' (or ''spatial size'') can refer to linear dimensions (length, width, height, diameter, perimeter), area, or volume. Size can also be measu ...

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, halos or haloes usually refer to: * Halo (optical phenomenon) * Halo (religious iconography), a ring of light around the image of a head HALO, halo, halos or haloes may also refer to: Arts and entertainment Video games * ''Halo'' (franch ...

s in that the latter are formed by

refraction In physics, refraction is the redirection of a wave as it passes from one 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 commonly observed phenomeno ...

(rather than diffraction) from comparatively large rather than small ice crystals. The diffraction pattern is called an

Airy disk In optics, the Airy disk (or Airy disc) and Airy pattern are descriptions of the best- focused spot of light that a perfect lens with a circular aperture can make, limited by the diffraction of light. The Airy disk is of importance in physics, ...

Pollen coronae

Pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...

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. The structure links the U.S. city of San Francisco, California—the northern tip of the San Francisco Pen ...

File:Iridescent fog.jpg, Partial Corona at

File:Moon Marki 19032011 3.JPG, Lunar aureole File:Janus24.jpg, Lunar corona with

Altocumulus floccus Altocumulus floccus is a cloud type named for its tuft-like, wooly appearance. The base of the cloud can form as low as , or as high as . They often form in clusters, or patches, and bases can vary in height with differing atmospheric conditions ...

File:Lunar corona.JPG, Lunar aureole as seen from

Mumbai Mumbai (, ; also known as Bombay — the official name until 1995) is the capital city of the Indian state of Maharashtra and the ''de facto'' financial centre of India. According to the United Nations, as of 2018, Mumbai is the second- ...

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. The term can also refer to the entire process of the solar disk crossing the horizon and its accompanying atmospheric effects. Terminology Al ...

Atmospheric optical phenomena {{climate-stub

Pollen coronae

See also

References

External links

Gallery