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Subhelic Arc
A subhelic arc is a rare halo, formed by internal reflection through ice crystals, that curves upwards from the horizon and touches the tricker arc above the anthelic point. Subhelic arcs result from ray entrance and exit through prism end faces with two intermediate internal reflections. Formation A subhelic arc is formed when sun rays enter one end face of an ice crystal in singly oriented columns and Parry columns, reflect off two of the crystals side faces, and exits the crystal through the opposite end face. The ray leaves the crystal at the exact opposite angle, resulting in a net deviation angle of 120°, the angle for the formation of 120° parhelia.Cowley, ''South Pole Halos - Zenith View'' The subhelic arc touches the top of the tricker arc, an indication the two have closely related ray paths.Cowley, ''South Pole Halos - Anthelic View'' The subhelic arc crosses the parhelic circle at an acute angle, and at a sun elevation of 27° it passes exactly through the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Halo (optical Phenomenon)
A halo is an optical phenomenon produced by light (typically from the Sun or Moon) interacting with ice crystals 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 or Moon, 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), light pillars, and sun dogs, but many others occur; some are fairly common while others are extremely rare. The ice crystals responsible for halos are typically suspended in cirrus or cirrostratus clouds in the upper troposphere (), but in cold weather they can also float near the ground, in which case they are referred to as diamond dust. The particular shape and orientation of the crystals are responsible for the type of halo observed. Light is reflected and refracted by the ice crystals and may split into colors because of dispersion. The crystals ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Internal Reflection
Total internal reflection (TIR) is the optical phenomenon in which waves arriving at the interface (boundary) from one medium to another (e.g., from water to air) are not refracted into the second ("external") medium, but completely reflected back into the first ("internal") medium. It occurs when the second medium has a higher wave speed (i.e., lower refractive index) than the first, and the waves are incident at a sufficiently oblique angle on the interface. For example, the water-to-air surface in a typical fish tank, when viewed obliquely from below, reflects the underwater scene like a mirror with no loss of brightness (Fig.1). TIR occurs not only with electromagnetic waves such as light and microwaves, but also with other types of waves, including sound and water waves. If the waves are capable of forming a narrow beam (Fig.2), the reflection tends to be described in terms of "rays" rather than waves; in a medium whose properties are independent of direction, such as air, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anthelic Point
The antisolar point is the abstract point on the celestial sphere directly opposite the Sun from an observer's perspective. This means that the antisolar point lies above the horizon when the Sun is below it, and vice versa. On a sunny day, the antisolar point can be easily found; it is located within the shadow of the observer's head. Like the zenith and nadir, the antisolar point is not fixed in three-dimensional space, but is defined relative to the observer. Each observer has an antisolar point that moves as the observer changes position. The antisolar point forms the geometric center of several optical phenomena, including subhorizon haloes, rainbows, glories, the Brocken spectre, and heiligenschein. Occasionally, around sunset or sunrise, anticrepuscular rays appear to converge toward the antisolar point near the horizon. However, this is an optical illusion caused by perspective; in reality, the "rays" (i.e. bands of shadow) run near-parallel to each other. Also arou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
120° Parhelion
A 120° parhelion (plural: 120° parhelia) is a relatively rare halo, an optical phenomenon occasionally appearing along with very bright sun dogs (also called parhelia) when ice crystal-saturated cirrus clouds fill the atmosphere. The 120° parhelia are named for appearing in pair on the parhelic circle ±120° from the sun. (including a HaloSim simulation.) When visible, 120° parhelia appear as white-bluish bright spots on the white parhelic circle and are the product of at least two interior reflections in the hexagonal ice crystals. Their colour together with them being rather obscure can make observing them difficult as they tend to fuse with the clouds in the sky. See also * 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 ... * Subhelic arc Refere ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Parhelic Circle
A parhelic circle is a type of halo, an optical phenomenon appearing as a horizontal white line on the same altitude as the sun, or occasionally the Moon. If complete, it stretches all around the sky, but more commonly it only appears in sections. If the halo occurs due to light from the moon rather than the sun, it is known as a paraselenic circle. Even fractions of parhelic circles are less common than sun dogs and 22° halos. While parhelic circles are generally white in colour because they are produced by reflection, they can however show a bluish or greenish tone near the 120° parhelia and be reddish or deep violet along the fringes. (including an excellent HaloSim simulation of a parhelic circle.) Parhelic circles form as beams of sunlight are reflected by vertical or almost vertical hexagonal ice crystals. The reflection can be either external (e.g. without the light passing through the crystal) which contributes to the parhelic circle near the sun, or internal (one or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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° halo, but in contrast to supralateral arcs, infralateral arcs are always located below the parhelic circle. The shape of an infralateral arc varies with the elevation of the Sun. Between sunrise and before the observed Sun reaches about 50° over Earth's horizon, two infralateral arcs are located on either side (e.g. lateral) of the 46° halo, their convex apexes lying tangent to the 46° halo. As the observed Sun reaches above 68° the two arcs unite to a single concave arc tangent to the 46° halo vertically under the Sun. (Including a photo from January 1996 and a 1980 computer simulation of infra- and supralateral arcs relative to a 46° halo.) Infralateral arcs form when sunlight enters horizontally oriented, rod-shaped hexagonal i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wegener Arc
Wegener may refer to: Astronomy * 29227 Wegener, a main-belt asteroid * Wegener (lunar crater) * Wegener (Martian crater) Places * Wegener Range, an Antarctic mountain range * Mount Wegener, an Antarctic mountain in the Read Mountains in the Shackleton Range * Wegener Canyon, an undersea canyon * Wegener Halvo Formation, a geologic formation in Greenland Businesses * Wegener (company), a Dutch media conglomerate * Alfred Wegener Institute for Polar and Marine Research Medicine * Wegener's granulomatosis, now known as granulomatosis with polyangiitis People * Alfred Wegener (1880–1930), German geologist who originated the theory of continental drift * ''Kapitänleutnant'' Bernhard Wegener, commander of German submarine ''U-27'', killed in one of the two Baralong incidents in 1915 * Bertha Frensel Wegener (1874–1953), Dutch composer and music educator * Bobby Wegener, American lawyer and Oklahoma's Secretary of Energy from 2008-2011 * Manuela (singer) (1943–2 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oulunsalo
Oulunsalo ( sv, Oulunsalo, also formerly ) is former municipality in the region of Northern Ostrobothnia, in Finland. Along with Haukipudas, Kiiminki and Yli-Ii it lost its municipal status and was merged with the city of Oulu on 1 January 2013. The municipality had a population of (31 December 2012) and covered an area of , of which is water. The population density is . The municipality was founded in 1882. Oulu Airport is located in Oulunsalo. Oulunsalo was one of the fastest-growing areas in Finland, among the other municipalities around Oulu. The municipality was unilingually Finnish. The municipality had also been known as ' in Swedish. The Swedish name is now considered outdated, according to the Institute for the Languages of Finland. Politics Results of the 2011 Finnish parliamentary election in Oulunsalo: * Centre Party 33.1% *True Finns 21.4% *National Coalition Party 15.9% * Left Alliance 10.9% *Social Democratic Party 8.9% *Green League 6.4% *Christi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oulu
Oulu ( , ; sv, Uleåborg ) is a city, municipality and a seaside resort of about 210,000 inhabitants in the region of North Ostrobothnia, Finland. It is the most populous city in northern Finland and the fifth most populous in the country after: Helsinki, Espoo, Tampere and Vantaa, and the fourth largest urban area in the country after Helsinki, Tampere and Turku. Oulu's neighbouring municipalities are: Hailuoto, Ii, Kempele, Liminka, Lumijoki, Muhos, Pudasjärvi, Tyrnävä and Utajärvi. Due to its large population and geopolitically economic and cultural-historical location, Oulu has been called the "capital of Northern Finland". Oulu is also considered one of Europe's "living labs", where residents experiment with new technology (such as NFC tags and ubi-screens) on a community-wide scale. Despite only ranking in the top 2% universities, the University of Oulu is regionally known in the field of information technology. Oulu has also been very successful in recent urban ima ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
