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Sun dogs (or sundogs), mock suns〔The American Heritage Dictionary of the English Language http://education.yahoo.com/reference/dictionary/entry/mock%20sun〕 or phantom suns,〔(Phantom Sun- 3 suns over China spotted )〕 scientific name parhelia (singular parhelion), are an atmospheric phenomenon that consists of a pair of bright spots on either side on the Sun, often co-occurring with a luminous ring known as a 22° halo.〔The American Heritage Dictionary of the English Language, 2004〕 Sun dogs are a member of a large family of halos, created by light interacting with ice crystals in the atmosphere. Sun dogs typically appear as two subtly colored patches of light to the left and right of the Sun, approximately 22° distant and at the same elevation above the horizon as the Sun. They can be seen anywhere in the world during any season, but they are not always obvious or bright. Sun dogs are best seen and are most conspicuous when the Sun is close to the horizon. ==Formation and characteristics== Sun dogs are commonly caused by the refraction of light from plate-shaped hexagonal ice crystals either in high and cold cirrus or cirrostratus clouds or, during very cold weather, drifting in the air at low levels, in which case they are called diamond dust.〔http://www.atoptics.co.uk/halo/diamonds.htm〕 The crystals act as prisms, bending the light rays passing through them with a minimum deflection of 22°. As the crystals gently float downwards with their large hexagonal faces almost horizontal, sunlight is refracted horizontally, and sun dogs are seen to the left and right of the Sun. Larger plates wobble more, and thus produce taller sundogs.〔(【引用サイトリンク】 Sundog formation )〕 Sun dogs are red-colored at the side nearest the Sun; farther out the colors grade through oranges to blue. However, the colors overlap considerably and so are muted, never pure or saturated.〔http://www.atoptics.co.uk/halo/dogcol.htm〕 The colors of the sun dog finally merge into the white of the parhelic circle (if the latter is visible).〔http://www.atoptics.co.uk/halo/parcirc.htm〕 The same plate shaped ice crystals that cause sun dogs are also responsible for the colorful circumzenithal arc, meaning that these two types of halo tend to co-occur.〔http://www.atoptics.co.uk/halo/czaform.htm〕 The latter is often missed by viewers, however, since it is located more or less directly overhead. Another halo variety often seen together with sun dogs is the 22° halo, which forms a ring at roughly the same angular distance from the sun as the sun dogs, thus appearing to interconnect them. As the Sun rises higher, however, the rays passing through the plate crystals are increasingly skewed from the horizontal plane, causing their angle of deviation to increase and the sun dogs to move farther from the 22° halo, while staying at the same elevation. It is possible to predict the forms of sun dogs as would be seen on other planets and moons. Mars might have sun dogs formed by both water-ice and CO2-ice. On the giant gas planets — Jupiter, Saturn, Uranus and Neptune — other crystals form the clouds of ammonia, methane, and other substances that can produce halos with four or more sun dogs. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sun dogs」の詳細全文を読む スポンサード リンク
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