Halo (optical Phenomenon)
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A halo 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 light (typically from the Sun or Moon) interacting with
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, n ...
suspended in the atmosphere. Halos can have many forms, ranging from colored or white rings to arcs and spots in the sky. Many of these appear near the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
or
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 ...
, but others occur elsewhere or even in the opposite part of the sky. Among the best known halo types are the circular halo (properly called the
22° halo A 22° halo is an atmospheric optical phenomenon that consists of a halo with an apparent radius of approximately 22° around the Sun or Moon. When visible around the Moon, it is also known as a moon ring or winter halo. It forms as sunlight o ...
),
light pillar A light pillar is an atmospheric optical phenomenon in which a vertical beam of light appears to extend above and/or below a light source. The effect is created by the reflection of light from tiny ice crystals that are suspended in the atmosp ...
s, and
sun dog A sun dog (or sundog) or mock sun, also called a parhelion (plural parhelia) in meteorology, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Sun. Two sun dogs often flank the Sun within a 22° ...
s, but many others occur; some are fairly common while others are extremely rare. The
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, n ...
responsible for halos are typically suspended in
cirrus Cirrus may refer to: Science *Cirrus (biology), any of various thin, thread-like structures on the body of an animal *Cirrus (botany), a tendril * Infrared cirrus, in astronomy, filamentary structures seen in infrared light *Cirrus cloud, a typ ...
or
cirrostratus cloud Cirrostratus is a high-level, very thin, generally uniform ''stratiform'' genus-type of cloud. It is made out of ice-crystals, which are pieces of frozen water. It is difficult to detect and it can make halos. These are made when the cloud takes t ...
s in the upper
troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
(), but in cold weather they can also float near the ground, in which case they are referred to as
diamond dust Diamond dust is a ground-level cloud composed of tiny ice crystals. This meteorological phenomenon is also referred to simply as ''ice crystals'' and is reported in the METAR code as IC. Diamond dust generally forms under otherwise clear or near ...
. The particular shape and orientation of the crystals are responsible for the type of halo observed.
Light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...
is reflected and
refracted 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 ...
by the
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, n ...
and may split into
color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
s because of
dispersion Dispersion may refer to: Economics and finance * Dispersion (finance), a measure for the statistical distribution of portfolio returns * Price dispersion, a variation in prices across sellers of the same item *Wage dispersion, the amount of variat ...
. The crystals behave like prisms and
mirror A mirror or looking glass is an object that Reflection (physics), reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the ...
s, refracting and reflecting light between their faces, sending shafts of light in particular directions.
Atmospheric optical phenomena Atmospheric optics is "the study of the optical characteristics of the atmosphere or products of atmospheric processes .... ncludingtemporal and spatial resolutions beyond those discernible with the naked eye". Meteorological optics is "that par ...
like halos were used as part of weather lore, which was an
empirical Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence is of central importance to the sciences and ...
means of
weather forecasting Weather forecasting is the application of science and technology forecasting, to predict the conditions of the Earth's atmosphere, atmosphere for a given location and time. People have attempted to predict the weather informally for millennia a ...
before
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 ...
was developed. They often do indicate that rain will fall within the next 24 hours, since the cirrostratus clouds that cause them can signify an approaching frontal system. Other common types of optical phenomena involving water droplets rather than ice crystals include the glory and
rainbow A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows c ...
.


History

While
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
had mentioned halos and parhelia, in antiquity, the first European descriptions of complex displays were those of
Christoph Scheiner Christoph Scheiner SJ (25 July 1573 (or 1575) – 18 June 1650) was a Jesuit priest, physicist and astronomer in Ingolstadt. Biography Augsburg/Dillingen: 1591–1605 Scheiner was born in Markt Wald near Mindelheim in Swabia, earlier markgrav ...
in Rome (circa 1630),
Johannes Hevelius Johannes Hevelius Some sources refer to Hevelius as Polish: * * * * * * * Some sources refer to Hevelius as German: * * * * *of the Royal Society * (in German also known as ''Hevel''; pl, Jan Heweliusz; – 28 January 1687) was a councillor ...
in Danzig (1661), and Tobias Lowitz in St Petersburg (c. 1794). Chinese observers had recorded these for centuries, the first reference being a section of the "Official History of the Chin Dynasty" (''Chin Shu'') in 637, on the "Ten Haloes", giving technical terms for 26 solar halo phenomena.


Vädersolstavlan

While mostly known and often quoted for being the oldest color depiction of the city of
Stockholm Stockholm () is the Capital city, capital and List of urban areas in Sweden by population, largest city of Sweden as well as the List of urban areas in the Nordic countries, largest urban area in Scandinavia. Approximately 980,000 people liv ...
, ''
Vädersolstavlan ''Vädersolstavlan'' (; ) is an Oil painting, oil-on-panel painting depicting a Halo (optical phenomenon), halo display, an Atmosphere, atmospheric optical phenomenon, observed over Stockholm on 20 April 1535. It is named after the sun dogs ( sv ...
'' (
Swedish Swedish or ' may refer to: Anything from or related to Sweden, a country in Northern Europe. Or, specifically: * Swedish language, a North Germanic language spoken primarily in Sweden and Finland ** Swedish alphabet, the official alphabet used by ...
; "The Sundog Painting", literally "The Weather Sun Painting") is arguably also one of the oldest known depictions of a halo display, including a pair of
sun dog A sun dog (or sundog) or mock sun, also called a parhelion (plural parhelia) in meteorology, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Sun. Two sun dogs often flank the Sun within a 22° ...
s. For two hours in the morning of 20 April 1535, the skies over the city were filled with white circles and arcs crossing the sky, while additional suns (i.e., sun dogs) appeared around the sun.


Light pillar

A light pillar, or sun pillar, appears as a vertical pillar or column of light rising from the sun near sunset or sunrise, though it can appear below the sun, particularly if the observer is at a high elevation or altitude. Hexagonal plate- and column-shaped ice crystals cause the phenomenon. Plate crystals generally cause pillars only when the sun is within 6 degrees of the horizon; column crystals can cause a pillar when the sun is as high as 20 degrees above the horizon. The crystals tend to orient themselves near-horizontally as they fall or float through the air, and the width and visibility of a sun pillar depend on crystal alignment. Light pillars can also form around the moon, and around street lights or other bright lights. Pillars forming from ground-based light sources may appear much taller than those associated with the sun or moon. Since the observer is closer to the light source, crystal orientation matters less in the formation of these pillars.


Circular halo

Among the best-known halos is the
22° halo A 22° halo is an atmospheric optical phenomenon that consists of a halo with an apparent radius of approximately 22° around the Sun or Moon. When visible around the Moon, it is also known as a moon ring or winter halo. It forms as sunlight o ...
, often just called "halo", which appears as a large ring around the Sun or Moon with a radius of about 22° (roughly the width of an outstretched hand at arm's length). The ice crystals that cause the 22° halo are oriented semi-randomly in the atmosphere, in contrast to the horizontal orientation required for some other halos such as sun dogs and light pillars. As a result of the optical properties of the ice crystals involved, no light is reflected towards the inside of the ring, leaving the sky noticeably darker than the sky around it, and giving it the impression of a "hole in the sky". The 22° halo is not to be confused with the
corona Corona (from the Latin for 'crown') most commonly refers to: * Stellar corona, the outer atmosphere of the Sun or another star * Corona (beer), a Mexican beer * Corona, informal term for the coronavirus SARS-CoV-2, which causes the COVID-19 di ...
, which is a different optical phenomenon caused by water droplets rather than ice crystals, and which has the appearance of a multicolored disk rather than a ring. Other haloes can form at 46° to the sun, or at the horizon, or around the zenith, and can appear as full haloes or incomplete arcs.


Bottlinger's ring

A ''Bottlinger's ring'' is a rare type of halo that is elliptical instead of circular. It has a small diameter, which makes it very difficult to see in the Sun's glare and more likely to be spotted around the dimmer Subsun, often seen from mountain tops or airplanes. Bottlinger's rings are not well understood yet. It is suggested that they are formed by very flat
pyramid A pyramid (from el, πυραμίς ') is a structure whose outer surfaces are triangular and converge to a single step at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilat ...
al ice crystals with faces at uncommonly low angles, suspended horizontally in the atmosphere. These precise and physically problematic requirements would explain why the halo is very rare.


Other names

In the
Anglo-Cornish The Cornish dialect (also known as Cornish English, Cornu-English, kw, Sowsnek Kernowek) is a dialect of English spoken in Cornwall by Cornish people. Dialectal English spoken in Cornwall is to some extent influenced by Cornish grammar, and o ...
dialect of English, a halo round the sun or the moon is called a ''cock's eye'' and is a token of bad weather. The term is related to the
Breton Breton most often refers to: *anything associated with Brittany, and generally ** Breton people ** Breton language, a Southwestern Brittonic Celtic language of the Indo-European language family, spoken in Brittany ** Breton (horse), a breed **Ga ...
word ''kog-heol'' (sun cock) which has the same meaning. In
Nepal Nepal (; ne, नेपाल ), formerly the Federal Democratic Republic of Nepal ( ne, सङ्घीय लोकतान्त्रिक गणतन्त्र नेपाल ), is a landlocked country in South Asia. It is mai ...
, the halo round the sun is called ''Indrasabha'' with a connotation of the assembly court of
Lord Indra Indra (; Sanskrit: इन्द्र) is the king of the devas (god-like deities) and Svarga (heaven) in Hindu mythology. He is associated with the sky, lightning, weather, thunder, storms, rains, river flows, and war.  volumes/ref> Ind ...
– the
Hindu god Hindu deities are the gods and goddesses in Hinduism. The terms and epithets for deities within the diverse traditions of Hinduism vary, and include Deva, Devi, Ishvara, Ishvari, Bhagavān and Bhagavati. The deities of Hinduism have evolved ...
of lightning, thunder and rain.


Artificial halos

The natural phenomena may be reproduced artificially by several means. Firstly, by computer simulations, or secondly by experimental means. Regarding the latter, one may either take a single crystal and rotate it around the appropriate axis/axes, or take a chemical approach. A still further and more indirect experimental approach is to find analogous refraction geometries.


Analogous refraction approach

This approach employs the fact that in some cases the average geometry of refraction through an ice crystal may be imitated / mimicked via the refraction through another geometrical object. In this way, the Circumzenithal arc, the
Circumhorizontal arc A circumhorizontal arc is an optical phenomenon that belongs to the family of ice halos formed by the refraction of sunlight or moonlight in plate-shaped ice crystals suspended in the atmosphere, typically in cirrus or cirrostratus clouds. In ...
and the suncave Parry arcs may be recreated by refraction through rotationally symmetric (i.e. non-prismatic) static bodies. A particularly simple table-top experiment reproduces artificially the colorful circumzenithal and circumhorizontal arcs using a water glass only. The refraction through the cylinder of water turns out to be (almost) identical to the rotationally averaged refraction through an upright hexagonal ice crystal / plate-oriented crystals, thereby creating vividly colored circumzenithal and the circumhorizontal arcs. In fact, the water glass experiment is often confused as representing a rainbow and has been around at least since 1920.Gilbert light experiments for boys – (1920), p. 98, Experiment No. 9
link
/ref> Following Huygens' idea of the (false) mechanism of the 22° parhelia, one may also illuminate (from the side) a water-filled cylindrical glass with an inner central obstruction of half the glasses' diameter to achieve upon projection on a screen an appearance which closely resembles parhelia (cf. footnote 9in Ref., or see hereWebpage detailing several DIY experiment
link
/ref>), i.e. an inner red edge transitioning into a white band at larger angles on both sides of the direct transmission direction. However, while the visual match is close, this particular experiment does not involve a fake caustic mechanism and is thus no real analogue.


Chemical approaches

The earliest chemical recipes to generate artificial halos has been put forward by Brewster and studied further by A. Cornu in 1889. The idea was to generate crystals by precipitation of a salt solution. The innumerable small crystals hereby generated will then, upon illumination with light, cause halos corresponding to the particular crystal geometry and the orientation / alignment. Several recipes exist and continue to be discovered. Rings are a common outcome of such experiments. But also Parry arcs have been artificially produced in this way.


Mechanical approaches


Single axis

The earliest experimental studies on halo phenomena have been attributed to Auguste Bravais in 1847."Mémoire sur les halos et les phénomènes optiques qui les accompagnent", 1847, J. de l'École Royale Polytechnique 31(18), p.1-270, §XXIV – Reproduction artificielle des phénomènes optiques dus à des prismes à axe vertical, Figures: PL I: Fig. 48, PL II: Fig: 49-54. Bravais used an equilateral glass prism which he spun around its vertical axis. When illuminated by parallel white light, this produced an artificial Parhelic circle and many of the embedded parhelia. Similarly, A. Wegener used hexagonal rotating crystals to produce artificial subparhelia. In a more recent version of this experiment, many more embedded parhelia have been found using commercially available hexagonal BK7 glass crystals. Simple experiments like these can be used for educational purposes and demonstration experiments. Unfortunately, using glass crystals one cannot reproduce the circumzenithal arc or the circumhorizontal arc due to total internal reflections preventing the required ray-paths when n<\sqrt. Even earlier than Bravais, the Italian scientist F. Venturi experimented with pointed water-filled prisms to demonstrate the circumzenithal arc. However, this explanation was replaced later by the CZA's correct explanation by Bravais. Artificial ice crystals have been employed to create halos which are otherwise unattainable in the mechanical approach via the use of glass crystals, e.g. circumzenithal and circumhorizontal arcs. The use of ice crystals ensures that the generated halos have the same angular coordinates as the natural phenomena. Other crystals such as NaF also have a refractive index close to ice and have been used in the past.


Two axes

In order to produce artificial halos such as the tangent arcs or the circumscribed halo one should rotate a single columnar hexagonal crystal about 2 axes. Similarly, the Lowitz arcs can be created by rotating a single plate crystal about two axes. This can be done by engineered halo machines. The first such machine was constructed in 2003; several more followed. Putting such machines inside spherical projection screens, and by the principle of the so-called sky transform,"Sky Transform" on atoptics.co.uk
link
/ref> the analogy is nearly perfect. A realization using micro-versions of the aforementioned machines produces authentic distortion-free projections of such complex artificial halos.Article with images on BoredPanda
Spherical projection screen for artificial halos
/ref> Finally, superposition of several images and projections produced by such halo machines may be combined to create a single image. The resulting superposition image is then a representation of complex natural halo displays containing many different orientation sets of ice prisms.


Three axes

The experimental reproduction of circular halos is the most difficult using a single crystal only, while it is the simplest and typically achieved one using chemical recipes. Using a single crystal, one needs to realize all possible 3D orientations of the crystal. This has recently been achieved by two approaches. The first one using pneumatics and a sophisticated rigging, and a second one using an Arduino-based random walk machine which stochastically reorients a crystal embedded in a transparent thin-walled sphere.


Gallery

File:Optical refraction in nightsky.jpg, 22° lunar halo behind coconut tree in Chikmagaluru on May 24th 2021 File:HaloSolar.jpg, 360 degree panorama of a parhelic circle and several other haloes in Madrid on March 25, 2017 File:Лунное гало.jpg, Long exposure of a night-time lunar halo display, including an
upper tangent arc Tangent arcs are a type of halo, an atmospheric optical phenomenon, which appears above and below the observed Sun or Moon, tangent to the 22° halo. To produce these arcs, rod-shaped hexagonal ice crystals need to have their long axis aligned ...
,
22° halo A 22° halo is an atmospheric optical phenomenon that consists of a halo with an apparent radius of approximately 22° around the Sun or Moon. When visible around the Moon, it is also known as a moon ring or winter halo. It forms as sunlight o ...
, and paraselenic circle File:Halointhesky.jpg, A
circumscribed halo In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius. Not every polyg ...
(outer ring, partially visible on the bottom left and top left/right) together with a 22° halo (inner ring) File:Sun pillar and kitesurfers.jpg, Sun pillar in San Francisco File:Halo padang.jpg,
22° halo A 22° halo is an atmospheric optical phenomenon that consists of a halo with an apparent radius of approximately 22° around the Sun or Moon. When visible around the Moon, it is also known as a moon ring or winter halo. It forms as sunlight o ...
around the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
, above PT Semen Padang building at
Padang Padang () is the capital and largest city of the Indonesian province of West Sumatra. With a Census population of 1,015,000 as of 2022, it is the 16th most populous city in Indonesia and the most populous city on the west coast of Sumatra. Th ...
,
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
, October 2, 2009, at 11:09 am File:Solar halo thermal.jpg, Atmospheric temperatures responsible for ice crystals around 22° halo, as viewed through a
thermal camera A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...
(°C). The halo itself is not present in the thermal spectrum. The sun is partially visible at the top of the image. File:Halo phantom-sun.jpg, Complex halo display (
22° halo A 22° halo is an atmospheric optical phenomenon that consists of a halo with an apparent radius of approximately 22° around the Sun or Moon. When visible around the Moon, it is also known as a moon ring or winter halo. It forms as sunlight o ...
,
sun dog A sun dog (or sundog) or mock sun, also called a parhelion (plural parhelia) in meteorology, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Sun. Two sun dogs often flank the Sun within a 22° ...
s,
upper tangent arc Tangent arcs are a type of halo, an atmospheric optical phenomenon, which appears above and below the observed Sun or Moon, tangent to the 22° halo. To produce these arcs, rod-shaped hexagonal ice crystals need to have their long axis aligned ...
, upper and lower Sun pillar, parhelic circle, supralateral arc) observed in Les Ménuires (elevation ≈2200 metres), Rhone-Alpes, France on January 23, 2015, during sunset at 16:30 File:Doppelsonne Halo Hoherodskopf Hessen 15-07-2017.jpg,
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
with
Sun dog A sun dog (or sundog) or mock sun, also called a parhelion (plural parhelia) in meteorology, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Sun. Two sun dogs often flank the Sun within a 22° ...
s at
Hoherodskopf Hoherodskopf is a mountain peak in the Vogelsberg of Hesse, Germany. It is a Miocene basaltic extinct volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to e ...
/
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
- July 15, 2017. File:9 degree pyramidal halo.png, A circumscribed halo (outer ring) together with a comparatively rare 9° halo (inner ring), caused by pyramidal ice crystals. Midsland, the Netherlands, 2019. File:IMG-20210524-WA0004.jpg, 22° halo around the Sun, above VBHC Serene Town at Bangalore, India, on May 24, 2021, at 12:15 pm File:Sun halo, Nov 1, 2021.jpg, Solar halo, at Cedar Key, Florida, US on November 1, 2021, about 15:26 EST File:Halo solar en Buenos Aires, Argentina (10 de diciembre de 2022).jpg, Halo around the Sun in Buenos Aires, Argentina (December 10, 2022)


See also

*
22° halo A 22° halo is an atmospheric optical phenomenon that consists of a halo with an apparent radius of approximately 22° around the Sun or Moon. When visible around the Moon, it is also known as a moon ring or winter halo. It forms as sunlight o ...
*
46° halo A 46° halo is a rare atmospheric optical phenomenon that consists of a halo with an apparent radius of approximately 46° around the Sun. At solar elevations of 15–27°, 46° halos are often confused with the less rare and more colourful su ...
* 120° parhelion *
Anthelion An anthelion (plural anthelia, from late Greek ανθηλιος, "opposite the sun") is a rare optical phenomenon of the halo family. It appears on the parhelic circle opposite to the sun as a faint white spot, not unlike a sundog, and may be c ...
*
Atmospheric optics Atmospheric optics is "the study of the optical characteristics of the atmosphere or products of atmospheric processes .... ncludingtemporal and spatial resolutions beyond those discernible with the naked eye". Meteorological optics is "that p ...
*
Circumhorizontal arc A circumhorizontal arc is an optical phenomenon that belongs to the family of ice halos formed by the refraction of sunlight or moonlight in plate-shaped ice crystals suspended in the atmosphere, typically in cirrus or cirrostratus clouds. In ...
*
Circumscribed halo In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius. Not every polyg ...
* Circumzenithal arc *
Corona Corona (from the Latin for 'crown') most commonly refers to: * Stellar corona, the outer atmosphere of the Sun or another star * Corona (beer), a Mexican beer * Corona, informal term for the coronavirus SARS-CoV-2, which causes the COVID-19 di ...
*
Diamond dust Diamond dust is a ground-level cloud composed of tiny ice crystals. This meteorological phenomenon is also referred to simply as ''ice crystals'' and is reported in the METAR code as IC. Diamond dust generally forms under otherwise clear or near ...
*
False sunrise A false sunrise is any of several atmospheric optical phenomena in which the Sun appears to have risen, but is actually still some distance below the horizon. A number of different atmospheric conditions can be responsible for this effect, all ...
* Glory *
Green flash The green flash and green ray are meteorological optical phenomena that sometimes occur transiently around the moment of sunset or sunrise. When the conditions are right, a distinct green spot is briefly visible above the Sun's upper limb; ...
*
Heiligenschein (; ) is an optical phenomenon in which a bright spot appears around the shadow of the viewer's head in the presence of dew. In photogrammetry and remote sensing, it is more commonly known as the hotspot. It is also occasionally known as Cellin ...
*
Infralateral arc An infralateral arc (or lower lateral tangent arc) is a rare halo, an optical phenomenon appearing similar to a rainbow under a white parhelic circle. Together with the supralateral arc they are always located outside the seldom observable 46° hal ...
*
Kern arc KERN (1180 AM) is a commercial radio station licensed to Wasco- Greenacres, California, and serving the Bakersfield metropolitan area. The station is owned by American General Media. The radio studios and offices are in the American General M ...
*
Light pillar A light pillar is an atmospheric optical phenomenon in which a vertical beam of light appears to extend above and/or below a light source. The effect is created by the reflection of light from tiny ice crystals that are suspended in the atmosp ...
*
Liljequist parhelion A Liljequist parhelion is a rare Halo (optical phenomenon), halo, an optical phenomenon in the form of a brightened spot on the parhelic circle approximately 150–160° from the sun; i.e., between the position of the 120° parhelion and the anthel ...
* Parhelic circle *
Parry arc A Parry arc is a rare halo, an optical phenomenon which occasionally appears over a 22° halo together with an upper tangent arc. Discovery The halo was first described by Sir William Edward Parry (1790–1855) in 1820 during one of his Arct ...
*
Rainbow A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows c ...
* Subhelic arc *
Subparhelic circle The subparhelic circle is a rare halo, an optical phenomenon, located below the horizon. It passes through both the subsun (below the Sun) and the antisolar point (opposite to the Sun). The subparhelic circle is the subhorizon counterpart to the p ...
* Subsun *
Sun dog A sun dog (or sundog) or mock sun, also called a parhelion (plural parhelia) in meteorology, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Sun. Two sun dogs often flank the Sun within a 22° ...
* Supralateral arc *
Tangent arc Tangent arcs are a type of halo, an atmospheric optical phenomenon, which appears above and below the observed Sun or Moon, tangent to the 22° halo. To produce these arcs, rod-shaped hexagonal ice crystals need to have their long axis aligned h ...


References


External links


Halo explanations and image galleries
a
Atmospheric Optics



Halo reports of interesting halo observations around the World

Southern Hemisphere Halo and other atmospheric phenomena

Halo in Chisinau Moldova (photo and video)

Walter Tape & Jarmo Moilanen, ''Atmospheric Halos and the Search for Angle x'' (free e-book)


– Hyperphysics {{authority control Atmospheric optical phenomena