Sun dog

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Pronounced sun dogs on both sides of a setting sun in New Ulm, Minnesota. Note the halo arcs passing through each sun dog.

An elongated parhelion alongside the sun, unseen at the left

A sun dog or sundog (scientific name parhelion, plural parhelia, for "beside the sun") is a common bright circular spot on a solar halo. It is an atmospheric optical phenomenon primarily associated with the reflection or refraction of sunlight by small ice crystals making up cirrus or cirrostratus clouds. Often, two sun dogs can be seen (one on each side of the sun) simultaneously.

[edit] Physical characteristics

Close-up of a parhelion exhibiting a range of colors due to the dependence of the refractive index of ice on wavelength

Sundogs appear on a cold day with blizzard conditions. This photograph was taken in the evening as the sun was setting in Fargo, North Dakota.

Sundogs typically, but not exclusively, appear when the sun is low, e.g. at sunrise and sunset, and the atmosphere is filled with ice crystal forming cirrus clouds, but diamond dust and ice fog can also produce them. They are often bright white patches of light looking much like the sun or a comet, and occasionally are confused with those phenomena. Sometimes they exhibit a spectrum of colours, ranging from red closest to the sun to a pale bluish tail stretching away from the sun.^[1] White sundogs are caused by light reflected off of atmospheric ice crystals, while colored sundogs are caused by light refracted through them.

The ice crystals causing atmospheric phenomenon are shaped as hexagonal prisms (ice I_h, e.g. with a hexagonal top and bottom and six rectangular sides). Some of these crystals are elongated, some are flat; the latter causing crisp and bright sundogs if evenly oriented with their hexagonal ends aligned horizontally, while the former produces other atmospheric phenomenon, such as parhelic circles, 22° halos, circumzenithal arcs, upper tangent arcs, and lower tangent arcs. A mixture of various crystals with different alignments produces several of these phenomena at the same time.^[1]

Variant of a parhelion at the South Pole. The sun is obscured.

When sunlight passes through the sides of a flat crystal, both the angle of the sun rays and the orientation of the crystals affects the shape and colour of the sundogs. Misaligned or wobbling crystals produce colourful and elongated sundogs, while light passing through the crystal in non-optimal deviation angles (up to 50°) produces the "tail" of the sundog stretching away from the sun. As refraction is dependent of wavelength, the sundogs tend to have red inner edges while the colours farther from the sun tend to be more bluish-white as colours increasingly overlap.^[1][2]

When the sun is low, the two sundogs are located on the circle of the 22° halo. As the sun rises, the sundogs slowly move along the parhelic circle away from the sun, finally, to vanish as the sun reaches 61° over the horizon^[1] (e.g. the sundogs move from the 22° halo to the circumscribed halo).^[3]

On Earth, the first planet (counting from the sun) with significant amounts of ice crystal-carrying clouds, the pair of sundogs flanking the sun are aligned with the horizon. On other planets and moons where water and ice are less prevalent, however, various crystal structures produce different halos. 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 sundogs.^[4]

In remote stretches of western Texas, sundog refers colloquially to a segment of a common rainbow.^{[citation needed]}

[edit] History

[edit] Egypt

There are records among the writings of the Ancient Egyptians that discuss two suns in the sky, and one that discusses the sun setting in the east, or moving backward.

[edit] Greece

Aristotle (Meteorology III.2, 372a14) notes that "two mock suns rose with the sun and followed it all through the day until sunset." He says that "mock suns" are always to the side, never above or below, most commonly at sunrise or sunset, more rarely in the middle of the day.

[edit] Cicero

An unusually pronounced sundog produced by sunlight passing through thin cirrus clouds. The true sun is located outside of the picture to the right.

A passage in Cicero's On the Republic (54-51 BC) is one of many by Greek and Roman authors who refer to sundogs and similar phenomena:

Be it so, said Tubero; and since you invite me to discussion, and present the opportunity, let us first examine, before any one else arrives, what can be the nature of the parhelion, or double sun, which was mentioned in the senate. Those that affirm they witnessed this prodigy are neither few nor unworthy of credit, so that there is more reason for investigation than incredulity.^[5]

[edit] Wars of the Roses

The prelude to the Battle of Mortimer's Cross is supposed to have involved the appearance of a complete parahelion with three "suns". The Yorkists took them to represent Edward of York, George of Clarence and Richard of Gloucester and their impending victory.

[edit] Jakob Hutter

Possibly the earliest clear description of a sun dog is by Jakob Hutter, who wrote in his Brotherly Faithfulness: Epistles from a Time of Persecution:

My beloved children, I want to tell you that on the day after the departure of our brothers Kuntz and Michel, on a Friday, we saw three suns in the sky for a good long time, about an hour, as well as two rainbows. These had their backs turned toward each other, almost touching in the middle, and their ends pointed away from each other. And this I, Jakob, saw with my own eyes, and many brothers and sisters saw it with me. After a while the two suns and rainbows disappeared, and only the one sun remained. Even though the other two suns were not as bright as the one, they were clearly visible. I feel this was no small miracle …^[6]

The observation most likely occurred in Auspitz (Hustopeče), Moravia in very late October or very early November of 1533. The original was written in German and is from a letter originally sent in November 1533 from Auspitz in Moravia to the Adige Valley in Tirol. The Kuntz Maurer and Michel Schuster mentioned in the letter left Jakob Hutter on the Thursday after the feast day of Simon and Jude, which is October 28. (This quote is also referenced by Fred Schaaf on page 94 of the November 1997 and December 1997 issues of Sky and Telescope.)

[edit] Vädersolstavlan

The so-called 'Sun Dog Painting' (Vädersolstavlan) depicting Stockholm in 1535 and the celestial phenomenon at the time interpreted as an ominous presage

While mostly known and often quoted for being the oldest colour depiction of the city of Stockholm, Vädersolstavlan (Swedish; "The Sundog Painting", literally "The Weather Sun Painting") is arguably also one of the oldest known depictions of a sun dog. For two hours in the morning of April 20, 1535, the skies over the city were filled with white circles and arcs crossing the sky, while additional suns appeared around the sun. The phenomenon quickly resulted in rumours of an omen of God's forthcoming revenge on King Gustav Vasa (1496-1560) for having introduced Protestantism during the 1520s and for being heavy-handed with his enemies allied with the Danish king.

Hoping to end speculations, the Chancellor and Lutheran scholar Olaus Petri (1493-1552) ordered a painting to be produced documenting the event. When confronted with the painting, the king, however, interpreted it as a conspiracy - the real sun of course being himself threatened by competing fake suns, one being Olaus Petri and the other the clergyman and scholar Laurentius Andreae (1470-1552), both thus accused of treachery, but eventually escaping capital punishment. The original painting is lost, but a copy from the 1630s survives and still can be seen in the church Storkyrkan in central Stockholm.^[7]

Woodcut of 1561 German event

[edit] Nuremberg, Germany in 1561

On April 14, 1561, the skies over Nuremberg, Germany were filled with a multitude of celestial objects that were observed by many people in the city. The objects were depicted five years later in the 1566 woodcut by Hans Glaser of the "1561 Nuremberg event", that is displayed to the right.^[8] Several of the images resemble the types of phenomenon that occur as parhelia.^{[original research?]}

[edit] Shackleton

A parhelion at the South Pole

In her history Shipwreck at the Bottom of the World: The Extraordinary True Story of Shackleton and the Endurance, telling the story of Endurance's ill-fated polar expedition in 1912, Jennifer Armstrong writes:

… All around them, too, were signs that the Antarctic winter was fast approaching: there were now twelve hours of darkness, and during the daylight hours petrels and terns fled toward the north. Skuas kept up a screeching clamor, and penguins on the move honked and brayed from the ice for miles around. Killer whales cruised the open leads, blowing spouts of icy spray. The tricks of the Antarctic atmosphere brought mock suns and green sunsets, and showers of jewel-colored ice crystals.^[9]

[edit] In fiction

A reference to 'parhelia' occurs in the Introduction to Vladimir Nabokov's 1962 novel Pale Fire:

The short (166) Canto One, with all those amusing birds and parhelia, occupies thirteen cards.^[10]

In the fifth novel of the Aubrey–Maturin series, Desolation Island, Patrick O'Brian writes:

A visit to the cabin showed him the glass lower still: sickeningly low. And back on the poop he saw that he was by no means the only one to have noticed the mounting sea – an oddly disturbed sea, as if moved by some not very distant force; white water too, and a strange green colour in the curl of the waves and in the water slipping by. He glanced north-west, and there the sun, though shining still, had a halo, with sun-dogs on either side. Ahead, the aurora had gained in strength: streamers of an unearthly splendour.^[11]

In her popular historical novel about Richard III of England, The Sunne in Splendour, Sharon Kay Penman writes:

Hastings laughed, too, and shook his head. 'Men do make their luck, Lady Margaret, and never have I seen that better proven than at Mortimer's Cross. For ere the battle, there appeared a most fearsome and strange sight in the sky.' He paused. 'Three suns did we see over us, shining full clear.'

In a footnote it is clarified: "Phenomenon known as a parhelion, generally caused by the formation of ice crystals in the upper air."

Two pages later, again mentioning the English king Edward IV, she adds: "Many, she saw, flaunted streaming sun emblems to denote her son's triumph under the triple suns at Mortimer's Cross."^[12]

Sundogs appear in the film The Deer Hunter. At the beginning of the film, as the men are leaving work, they see the phenomenon. Robert De Niro's character describes it as an 'old Indian thing' and "A blessing on the hunter sent by the great wolf to his children".

The horror fiction writer Stephen King has a novella called The Sun Dog.

Sun dogs are referenced metaphorically in Rush's 1989 classic hit "Chain Lightning" on the album Presto. Neil Peart has been quoted as saying that they are "an inspiration for his lyrics."^[13]

The band Of Montreal used the image in the lyrics to "The Past Is a Grotesque Animal" on the 2007 album Hissing Fauna, Are You the Destroyer?^[14]:

I've played the unraveler, the parhelion
But even Apocalypse is fleeting
There's no death, no ugly world

The British neofolk band Death in June put out an EP called "Sun dogs" in 1994.

Jack London has a short story called The Sun Dog Trail.

One of Robert Rauschenberg's early experiments in 1962 employing the silk-screen process to reuse previously published images in "Combine Paintings" is titled "Sun Dog".

[edit] See also

• 120° parhelion
• Liljequist parhelion
• Anthelion
• Moon dog
• The miracle of the sun
• Circumhorizontal arc

[edit] References

[edit] External links

Wikimedia Commons has media related to:

Sun dog

Look up sun dog, parhelion in Wiktionary, the free dictionary.

• Sundogs - Parhelia, Explanations and Images, Les Cowley's Atmospheric Optics site
• Optical Phenomena - Photos of sun dogs
• Starry Night Photography - Sun Dog, Sun Halo, Moon Halo - Some photos and some text
• Atmospheric Optics - Ice Halos
• Sundog Splendor! video with marvelous close-ups