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A sun dog or mock sun, also called a parhelion 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° halo.
A halo is an optical phenomenon produced by light 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, light pillars, and sun dogs, but many others occur; some are fairly common while others are extremely rare.
Sotkamo is a municipality of Finland, located in the Kainuu region about 40 kilometres (25 mi) east of Kajaani, the capital of Kainuu. Vuokatti, in west of Sotkamo, is the most populous village in the municipality and also a popular skiing resort. The Hiidenportti National Park is located in the municipality.
An anthelion 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 crossed by an X-shaped pair of diffuse arcs.
A moon dog or mock moon, also called a paraselene in meteorology, is an atmospheric optical phenomenon that consists of a bright spot to one or both sides of the Moon. They are exactly analogous to sun dogs.
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 its full form, the arc has the appearance of a large, brightly spectrum-coloured band running parallel to the horizon, located far below the Sun or Moon. The distance between the arc and the Sun or Moon is twice as far as the common 22-degree halo. Often, when the halo-forming cloud is small or patchy, only fragments of the arc are seen. As with all halos, it can be caused by the Sun as well as the Moon.
The circumzenithal arc, also called the circumzenith arc (CZA), upside-down rainbow, and the Bravais arc, is an optical phenomenon similar in appearance to a rainbow, but belonging to the family of halos arising from refraction of sunlight through ice crystals, generally in cirrus or cirrostratus clouds, rather than from raindrops. The arc is located at a considerable distance above the observed Sun and at most forms a quarter of a circle centered on the zenith. It has been called "a smile in the sky", its first impression being that of an upside-down rainbow. The CZA is one of the brightest and most colorful members of the halo family. Its colors, ranging from violet on top to red at the bottom, are purer than those of a rainbow because there is much less overlap in their formation.
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.
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 or moonlight is refracted by millions of hexagonal ice crystals suspended in the atmosphere. Its radius is roughly the length of an outstretched hand at arm's length.
A 120° parhelion is a relatively rare halo, an optical phenomenon occasionally appearing along with very bright sun dogs 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.
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 horizontally.
A circumscribed halo is a type of halo, an optical phenomenon typically in the form of a more or less oval ring that circumscribes the circular 22° halo centred on the sun or moon. As the sun rises above 70° it essentially covers the 22° halo. Like many other halos, it is slightly reddish on the inner edge, facing the sun or moon, and bluish on the outer edge.
A supralateral arc is a comparatively rare member of the halo family which in its complete form appears as a large, faintly rainbow-colored band in a wide arc above the sun and appearing to encircle it, at about twice the distance as the familiar 22° halo. In reality, however, the supralateral arc does not form a circle and never reaches below the sun. When present, the supralateral arc touches the circumzenithal arc from below. As in all colored halos, the arc has its red side directed towards the sun, its blue part away from it.
An infralateral 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.
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 supralateral and infralateral arcs, which cross the parhelic circle at about 46° to the left and right of the sun.
A Parry arc is a rare halo, an optical phenomenon which occasionally appears over a 22° halo together with an upper tangent 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 are a result of ray entrance and exit through prism end faces with two intermediate internal reflections.
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 of which divert the sunlight in such a way as to allow it to reach the observer's eye, thereby giving the impression that the light comes directly from the Sun itself. The spread of light can sometimes be deceivingly similar to a true sun.
Atmospheric optics is "the study of the optical characteristics of the atmosphere or products of atmospheric processes .... [including] temporal and spatial resolutions beyond those discernible with the naked eye". Meteorological optics is "that part of atmospheric optics concerned with the study of patterns observable with the naked eye". Nevertheless, the two terms are sometimes used interchangeably.
A Lowitz arc is an optical phenomenon that occurs in the atmosphere; specifically, it is a rare type of ice crystal halo that forms a luminous arc which extends inwards from a sun dog (parhelion) and may continue above or below the sun.
References
- ↑ S. W. Visser: Optische verschijnselen aan de hemel, bladzijde 58, § 44: De gespiegelde circumzenitale boog. Boog van Kern
- 1 2 Mikkilä, Marko (2008-01-27). "Kern arc photographed in Finland". ursa.fi. URSA. Archived from the original on 2008-02-07. Retrieved 2008-01-30. (Mikkilä's description of the observation.)
- ↑ Cowley, Les. "Kern Arc". Atmospheric Optics. Retrieved 2008-01-27.
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