page_title: Vädersolstavlan
section_title: Halo display
hierarchical_section_title: Vädersolstavlan / Halo display
caption_attribution_description: Detail from Vädersolstavlan showing a w:120° parhelion and an w:Anthelion on a w:Parhelic circle.
context_page_description: Vädersolstavlan is an oil-on-panel painting depicting a halo display, an atmospheric optical phenomenon, observed over Stockholm on 20 April 1535. It is named after the sun dogs appearing on the upper right part of the painting. While chiefly noted for being the oldest depiction of Stockholm in colour, it is arguably also the oldest Swedish landscape painting and the oldest depiction of sun dogs.
  The original painting, which was produced shortly after the event and traditionally attributed to Urban målare, is lost, and virtually nothing is known about it. However, a copy from 1636 by Jacob Heinrich Elbfas held in Storkyrkan in Stockholm is believed to be an accurate copy and was until recently erroneously thought to be the restored original. It was previously covered by layers of brownish varnish, and the image was hardly discernible until carefully restored and thoroughly documented in 1998–1999.
  The painting was produced during an important time in Swedish history. The establishment of modern Sweden coincided with the introduction of Protestantism and the break-up with Denmark and the Kalmar Union.
context_section_description: While the painting is arguably the oldest realistic depiction of a halo phenomenon — almost a century older than Christoph Scheiner's famous observation of a halo display over Rome in 1630 — the phenomenon was apparently not entirely understood. The image contains several obvious misinterpretations and a few peculiarities.  Most notably, like many other early depictions of haloes, the painting depicts a series of events occurring over several hours and is consistent in its preference for perfect circles rather than ellipses.
  A work of art produced in the spirit of the Danube School (see Possible prototypes above), Vädersolstavlan features realistic depictions of cirrus clouds and the sky is properly rendered, going from bright blue near the horizon to dark blue near zenith. The shadows in the lower half of the painting, however, seem to suggest the sun is located in the west — even leaving the southern façades in shadow — which is incorrect as historical sources claim the event lasted from 7 to 9 a.m.  In contrast to the city below it, the halo phenomenon is depicted vertically in a fisheye perspective with the major circle centred on zenith (like in the ray tracing solution above).
  In the painting, the actual sun is the yellow ball in the upper-right corner surrounded by the second circle.  The large circle taking up most of the sky is a parhelic circle, parallel to the horizon and located at the same altitude as the sun, as the painting renders it.  This is actually a common halo, although a full circle as depicted is rare.  Such parhelic circles are caused by horizontally oriented plate ice crystals reflecting sun rays.  In order for a full circle to appear sun rays must be reflected both internally and externally.
  The circle surrounding the sun is a 22° halo, as the name implies located 22° from the sun.  While the painting depict it pretty much as it normally appears, it should be centred on the sun and is misplaced in the painting.
  The pair of arcs flanking the 22° halo and crossing each other are most likely a misinterpretation of a circumscribed halo.  While the sun is still low, it starts as a V-shaped upper tangent arc which gradually develops into something looking like the unfolding wings of a seagull. As the sun ascends, in rare cases it finally joins with the lower tangent arc to form an ellipse which closes in on the circumscribed 22° halo.
  The sun dogs or parhelia, in the painting erroneously pinned to the misinterpreted arcs of the circumscribed halo, are rather frequent optical phenomena which appear when sunlight is refracted by hexagonal ice crystals forming cirrus or cirrostratus clouds.  When the sun is still low, they are located on the 22° halo, the way they are most commonly observed, and as the sun ascends they move laterally away from the 22° halo.  At rare occasions, they can actually reach the circumscribed halo.  As depicted in the painting, the sun dogs are located midway between the 22° halo and the circumscribed halo, and, assuming they are correctly rendered, the sun should have been located at about 35–40° above the horizon (as in the simulation above).
  The unintelligible arc on the lower right might be a misinterpreted and misplaced infralateral arc missing its mirrored twin.  These phenomena are, however, rare and only form when the sun is below 32°. Their shape change quickly as the sun rises, and as the painting most likely isn't depicting any specific moment, it is impossible to draw any conclusions from the mysterious shape in the painting.
  The crescent moon shape in the middle of the sky looks very much like a circumzenithal arc, which is parallel to the horizon but centred at and located near zenith.  However, they only form when the sun is located lower than 32.2° and are at their brightest when the sun is located at 22°, which is not consistent with other haloes depicted in the painting.  Furthermore, one of the most striking features of circumzenithal arcs is their rainbow colours, and the shape in the painting is perfectly devoid of any colours. It is however not a complete 
caption: A 120° parhelion (top) and the anthelion (bottom) from the painting
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