Parhelia / Sundogs (EE02/03)

Bright patches of light to the right and left of the sun are called sundogs. They are found at the sun's height parallel to the horizon. Their distance from the low-hanging sun is 22°. They are thus on the small circle. With the sun high in the sky, the sundogs increasingly move away from the 22°-ring. When the sun is 40° above the horizon, the sundogs have a distance of about 27.6°. Above a sun height of about 61°, sundogs can no longer form. In Central Europe they are therefore not visible around noon in summer. Sundogs often show a very intense coloration. They are red towards the sun and, in full form, have a long white tail pointing away from the sun parallel to the horizon. The red is followed by yellow. Blue is usually only faintly visible on the side facing away from the sun, in front of the white tail. The tail is part of the parhelic circle. The brightness of the sundogs can be so strong in exceptional cases that one is almost dazzled. When the moon is bright, moondogs form in the same way. Sundogs often appear together with the 22° ring and the upper tangent arc. Related phenomena are the 120° parhelia and the subparhelia.

Parhelia are formed on hexagonal ice prisms with a plate shape. When the plates fall undisturbed, they automatically assume a horizontal position. The sunlight enters one prism face and exits at the next prism face. The connection between the parhelia and the circumzenithal arc is interesting. Both occur in horizontally aligned ice plates. Therefore, when parhelia appear, one can also expect the circumzenithal arc, especially at a sun height between 15° and 25°.