Sun Dog
A sun dog (or sundog)
or mock sun, formally called a parhelion (plural parhelia)
in meteorology, is an atmospheric optical phenomenon that
consists of a bright spot to the left or right of the Sun. Two sun dogs
often flank the Sun within a 22° halo.
The sun dog is a member of the family
of halos, caused by the refraction of sunlight by ice
crystals in the atmosphere. Sun dogs typically appear as a pair of subtly
colored patches of light, around 22° to the left and right of the
Sun, and at the same altitude above the horizon as the Sun. They can be
seen anywhere in the world during any season, but are not always obvious or
bright. Sun dogs are best seen and most conspicuous when the Sun is near the
horizon.
A Sun
halo, a circle of light that creates a circle 22° wide around the Sun, is a
related phenomenon. As with sundogs, hexagonal ice crystals suspended in
cirrostratus clouds refract sunlight to create the halo, sometimes also called
an ice bow, nimbus, or gloriole. Unlike sundogs, which generally only be seen
when the Sun is near the horizon, the halo is visible even when the Sun is
high. Sundogs appear along the 22° halo and disappear as the Sun rise. There
are also moon dogs that appear alongside the moon and are formed by lunar light
passing through ice crystals. Moon dogs, or paraselenae, are not observed as
often as sundogs because they are visible when the moon is bright and
because they appear during the night.
Origin
Sundogs are formed from hexagonal ice
crystals in high and cold cirrus clouds or, during very cold weather, by ice
crystals drifting in the air at low levels. These crystals act as prisms,
bending the light rays passing through them. As the crystals sink through the
air they become vertically aligned, refracting the sunlight horizontally so
that sundogs are observed.
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Credit:
Yongwon Kim , University of Alaska Fairbanks
Sundogs frequently display a reddish tint on
the side facing the sun and may sport bluish-white tails that stretch
horizontally away from it. The sundog's tail is formed by light passing through
the crystal at angles other than the optimal deviation angle.
Just because they are formed from ice
crystals does not mean that sundogs can only be observed in cold climates. They
can occur at any time of the year and from any place, although they are most
visible when the sun is lower on the horizon in January, April,
August and October. They also occur when ice crystals in the atmosphere are
more common, but can be seen whenever and wherever there are cirrus clouds.
As the sun rises, the sundog can actually
drift away from the 22-degree point. Eventually the sun rises to a higher point
to where the sundog completely disappears.
Ancient Greeks came to realize that sundogs
are fairly accurate rain forecasters. The ice crystals that produce the haloes
and sundogs also form cirroform clouds, which make up the typical cloud
formation that foretells a precipitating warm front.
Characteristics
1. It
caused by refraction of sunlight.
2. It
formed mainly in cold weather. A sun dog could be seen from polar or sub polar
region.
3. It
could be seen during day only.
4. Sun
dogs are red coloured at the side nearest the sun; further out the colours
grade through oranges to blue.
5. The
colours of the sun dog overlap considerably and are muted, never pure or
saturated.
6. Sometimes
it creates a small rainbow called ‘ sun dog rainbow’.
Sun dog rainbow
History
There
are many mentions of sundogs in history in literature, art and scientific
papers.
1. Many
Greek and Roman authors provide detailed descriptions of sundogs. The Greek
philosopher Aristotle (384 B.C. – 322 B.C.) notes that "two mock suns rose
with the sun and followed it all through the day until sunset," noting
that they are always to the side, never above or below the sun. The Greek poet
Aratus (ca. 315 B.C./310 B.C. – 240 B.C.) mentions sundogs in his catalog of
weather signs. In his "On the Republic," Cicero shares a detailed
description of the phenomenon.
2.
Jacob Hutter (ca 1500 – Feb. 25, 1536), a founder of
the Anabaptist movement in what is now Italy, described sundogs in his work,
"Brotherly Faithfulness: Epistles from a Time of Persecution."
Sun dog phenomenon depicted
in the Nuremberg Chronicle
3.
The "Sundog Painting" (Vädersolstavlan) depicts
sundogs in Stockholm in 1535. The original painting, which was produced shortly
after the event and typically attributed to Urban Målare is lost. However, a
1636 copy by Jacob Heinrich Elbfas still exists.
The so-called "Sun Dog Painting" (Vädersolstavlan)
depicting Stockholm in 1535 and
the celestial phenomenon at the time interpreted as an ominous presage
4. Stephen
King wrote about the phenomenon in a short story called "The Sun Dog"
in his "Four Past Midnight" collection of short stories. And in
"King Henry VI, Part 3," William Shakespeare dramatized the
appearance of sundogs during the War of the Roses.
References
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Darun
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