Kern arc
Encyclopedia
The Kern arc is the extremely rare atmospheric optical phenomenon
related to the circumzenithal arc
. It is a complete and faint circle around the zenith. In contrast, the related and much more common circumzenithal arc is only ever a partial circle.
The Kern arc is named after H. F. A. Kern in the Netherlands, who first reported it in 1895. Since then it has been reported on six occasions.
It is formed by rays entering the top faces of horizontal plate crystals and leaving through a near vertical side face. Kern arc rays undergo an internal reflection off a side face inclined at 60 degrees to the exit face. Near triangular hexagonal crystals with three alternate side faces much shorter than the others allow Kern arc.
The first photographs of the Kern arc were taken by Marko Mikkilä close to Vuokatti Ski Resort Sotkamo
, Finland
on 17 November 2007. The photographs were in natural sunlight taken from an artificial cloud created by snowguns. At the Vuokatti Ski Resort about 100 snowguns may operate at one time. The temperature was -15 to -18C in clear sky and almost no wind. Nikon D70 and Nikon FM cameras were used with Sigma 8mm EX F4,
Sigma 15mm EX F2.8 lenses. Some samples of ice crystals were also collected confirming their nearly triangular base.
Mikkiläs photographs were first published in Tähdet ja avaruus-magazine 1/2008. The magazine is published by URSA
, the Finnish association of astronomy.
Optical phenomenon
An optical phenomenon is any observable event that results from the interaction of light and matter. See also list of optical topics and optics. A mirage is an example of an optical phenomenon....
related to the circumzenithal arc
Circumzenithal arc
The circumzenithal arc or circumzenith arc , also called the Bravais' arc, is an optical phenomenon similar in appearance to a rainbow; but it arises from refraction of sunlight through horizontally-oriented ice crystals, generally in cirrus clouds, rather than from raindrops...
. It is a complete and faint circle around the zenith. In contrast, the related and much more common circumzenithal arc is only ever a partial circle.
The Kern arc is named after H. F. A. Kern in the Netherlands, who first reported it in 1895. Since then it has been reported on six occasions.
It is formed by rays entering the top faces of horizontal plate crystals and leaving through a near vertical side face. Kern arc rays undergo an internal reflection off a side face inclined at 60 degrees to the exit face. Near triangular hexagonal crystals with three alternate side faces much shorter than the others allow Kern arc.
The first photographs of the Kern arc were taken by Marko Mikkilä close to Vuokatti Ski Resort Sotkamo
Sotkamo
Sotkamo is a municipality of Finland, located in the Kainuu region. The municipality has a population of and covers an area of of which is water. The population density is .Vuokatti, west of Sotkamo, is a popular skiing resort...
, Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
on 17 November 2007. The photographs were in natural sunlight taken from an artificial cloud created by snowguns. At the Vuokatti Ski Resort about 100 snowguns may operate at one time. The temperature was -15 to -18C in clear sky and almost no wind. Nikon D70 and Nikon FM cameras were used with Sigma 8mm EX F4,
Sigma 15mm EX F2.8 lenses. Some samples of ice crystals were also collected confirming their nearly triangular base.
Mikkiläs photographs were first published in Tähdet ja avaruus-magazine 1/2008. The magazine is published by URSA
Ursa (Finland)
Ursa Astronomical Association is the largest astronomical association in Finland. Ursa was founded on 2 November 1921. Founding members include a renowned Finnish astronomer Yrjö Väisälä. In 1926 Ursa established the Ursa Observatory in Kaivopuisto district of Helsinki. Ursa's primary functions...
, the Finnish association of astronomy.