Asun dog (orsundog) ormock sun, also called aparhelion[1] (pluralparhelia) inatmospheric science, is anatmosphericoptical phenomenon that consists of a bright spot to one or both sides of theSun. Two sun dogs often flank the Sun within a22° halo.
The sun dog is a member of the family ofhalos caused by therefraction of sunlight byice 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 samealtitude 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.
Sun dogs are commonly caused by therefraction andscattering of light from horizontally oriented[2] plate-shapedhexagonalice crystals eithersuspended in high and coldcirrus orcirrostratus clouds, or drifting in freezing moist air at low levels asdiamond dust.[3] The crystals act asprisms, 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 sun dogs.[4]
Sun dogs are red-colored at the side nearest the Sun; farther out the colors grade through oranges to blue. The colors overlap considerably and are muted, never pure or saturated.[5] The colors of the sun dog finally merge into the white of theparhelic circle (if the latter is visible).[6]
The same plate-shaped ice crystals that cause sun dogs are also responsible for the colorfulcircumzenithal arc, meaning that these two types of halo tend to co-occur.[7] The latter is often missed by viewers, since it is located more or less directly overhead. Another halo variety often seen together with sun dogs is the22° 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, 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.[8]
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 thegiant planets—Jupiter,Saturn,Uranus, andNeptune—other crystals form clouds ofammonia,methane, and other substances that can produce halos with four or more sun dogs.[9]
A related phenomenon, theCrown flash is also known as a "leaping Sundog".
A somewhat common misconception among the general public is to refer to any member of the icehalo family as a "sun dog" (especially the22° halo, being one of the most common varieties). However, sun dogs represent just one of many different types of halos. For referring to the atmospheric phenomenon in general, the term(ice crystal) halo(s) is more appropriate.
The exact etymology ofsun dog largely remains a mystery. TheOxford English Dictionary says it is "of obscure origin".[10]
In Abram Palmer's 1882 bookFolk-etymology: A Dictionary of Verbal Corruptions Or Words Perverted in Form Or Meaning, by False Derivation Or Mistaken Analogy, sun-dogs are defined:
The phenomena [sic] of false suns which sometimes attend or dog the true when seen through the mist (parhelions). In Norfolk asun-dog is a light spot near the sun, andwater-dogs are the light watery clouds;dog here is no doubt the same word asdag, dew or mist as "a littledag of rain" (Philolog. Soc. Trans. 1855, p. 80).Cf. Icel.dogg, Dan. and Swed.dug = Eng. "dew."[11]
Other sources observe thatDog in English as a verb can mean "hunt, track, or follow",[12] soDog the true [sun] has meanttrack the true [sun] since the 1510s.[13]
Alternatively, Jonas Persson suggested that out ofNorse mythology and archaic names —Danish:solhunde (sun dog),Norwegian:solhund (sun dog),Swedish:solvarg (sun wolf) — in the Scandinavian languages, constellations oftwowolves hunting the Sun and the Moon, one after and one before, may be a possible origin for the term.[14]
Parhelion (pluralparhelia) comes fromAncient Greek:παρήλιον (parēlion, 'beside the sun'; fromπαρά (para, 'beside') andἥλιος (helios, 'sun')).[15]
In theAnglo-Cornish dialect ofCornwall,United Kingdom, sun dogs are known asweather dogs (described as "a short segment of a rainbow seen on the horizon, foreshowing foul weather"). It is also known asa lagas in the sky which comes from theCornish language term for the sun doglagas awel meaning 'weather's eye' (lagas, 'eye' andawel, 'weather/wind'). This is in turn related to the Anglo-Cornish termcock's eye for a halo round the Sun or the Moon, also aportent of bad weather.[16]
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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.[17]
The poetAratus (Phaenomena, lines 880–891) mentions parhelia as part of his catalogue of Weather Signs; according to him, they can indicate rain, wind, or an approaching storm.[18]
Artemidorus in hisOneirocritica ('On the Interpretation of Dreams') included the mock suns amongst a list of celestial deities.[19]
A passage inCicero'sOn the Republic (54–51 BC) is one of many Roman authors who refer to sun dogs and similar phenomena:
... 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.[20]
Seneca makes an incidental reference to sun dogs in the first book of hisNaturales Quaestiones.[21]
Pliny the Elder references accounts of sun dogs in the 31st chapter of the 2nd book of hisHistoria Naturalis:
... many suns have been seen at the same time; not above or below the real sun, but in an oblique direction, never near nor opposite to the earth, nor in the night, but either in the east or in the west. ... We have no account transmitted to us of more than three having been seen at the same time.[22]
The 2nd-century Roman writer and philosopherApuleius in hisApologia says "What is the cause of the prismatic colours of the rainbow, or of the appearance in heaven of two rival images of the sun, with sundry other phenomena treated in a monumental volume byArchimedes of Syracuse."[23]
Fulcher of Chartres, writing in Jerusalem in the early twelfth century, notes in hisHistoria Hierosolymitana (1127) that on February 23, 1106
... from the third hour (9 am) until midday, we saw left and right from the Sun what looked like two other Suns: they did not shine like the big one, but smaller in appearance and radiance they reddened moderately. Above their circle a halo appeared, shining very brightly, extending in its breadth as if it were some kind of city. Inside this circle a half-circle appeared, similar to a rainbow, distinct in its fourfold color, in the higher part curved towards the two aforementioned Suns, touching them in an embrace of the Sun.[24]
[1551] And also abowte Ester was sene in Sussex three sonnes shenynge at one tyme in the eyer, that thei cowde not dysserne wych shulde be the very sonne.
The prelude to theBattle of Mortimer's Cross inHerefordshire,England in 1461 is supposed to have involved the appearance of a halo display with three "suns". TheYorkist commander, laterEdward IV of England, convinced his initially frightened troops that it represented the three sons of the Duke of York, and Edward's troops won a decisive victory. The event was dramatized byWilliam Shakespeare inKing Henry VI, Part 3,[25] and bySharon Kay Penman inThe Sunne In Splendour.
Another early clear description of sun dogs is byJacob Hutter, who wrote in hisBrotherly 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…[26]
The observation most likely occurred inAuspitz (Hustopeče),Moravia on 31 October 1533. The original was written in German and is from a letter originally sent in November 1533 from Auspitz in Moravia to theAdige Valley inSouth Tyrol. The Kuntz Maurer and Michel Schuster mentioned in the letter left Hutter on the Thursday after the feast day ofSimon andJude, which is 28 October. The Thursday after was 30 October.[27] It is likely that the "two rainbows with their backs turned toward each other, almost touching" involved two further halo phenomena, possibly acircumzenithal arc (prone to co-occur with sun dogs) together with a partial46° halo orsupralateral arc.[28]
While mostly known and often quoted for being the oldest color depiction of the city ofStockholm,Vädersolstavlan (Swedish; "The Sundog Painting", literally "The Weather Sun Painting") is arguably[citation needed] also one of the oldest known depictions of a halo display, including a pair of sun dogs. For two hours in the morning of 20 April 1535, the skies over the city were filled with white circles and arcs crossing the sky, while additional suns (i.e., sun dogs) appeared around the sun. The phenomenon quickly resulted in rumours of anomen of God's forthcoming revenge on KingGustav Vasa (1496–1560) for having introducedProtestantism during the 1520s and for being heavy-handed with his enemies allied with the Danish king.[citation needed]
Hoping to end speculations, the ChancellorOlaus Petri (1493–1552), aLutheran scholar, 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 scholarLaurentius Andreae (1470–1552). Both were thus accused of treachery, but eventually escaped capital punishment. The original painting is lost, but a copy from the 1630s survives and can still be seen in the churchStorkyrkan in central Stockholm.
A series of complex parhelia displays in Rome in 1629, and again in 1630, were described byChristoph Scheiner in his bookParhelia, one of the earliest works on the subject. It had a profound effect, causingRené Descartes to interrupt his metaphysical studies and led to his work of natural philosophy calledThe World.[29]
On 20 February 1661 the people ofGdańsk witnesseda complex halo display, described by Georg Fehlau in a pamphlet, theSevenfold Sun Miracle, and again the following year byJohannes Hevelius in his book,Mercurius in Sole visus Gedani.
On 18 June 1790Johann Tobias Lowitz, inSaint Petersburg, Russia, observed a complex display of haloes and parhelia which included hisLowitz arcs.
In 1843, winter in the British Colony ofNewfoundland was referred to as the 'Winter of Three Suns' and was unusually cold with 15 days of temperatures between 3–10 degrees below zero.[30]
"Part of the time we marched in the teeth of a biting storm of snow, and at every hour of the day the sun could be discerned sulking behind soft grey mists in company with rivals, known in the language of the plains as 'Sun-dogs', whose parahelic splendors warned the traveler of the approach of the ever-to-be-dreaded 'blizzard'."[31][who said this?]
On 14 February 2020, the people of Inner Mongolia Autonomous Region witnessed a different complex halo display called the Five-fold sun miracle, in which all five sun halos were linked to each other by rays, forming a circle among them.[32]
