Optical Effects
Rainbow I
Rainbow II
Rainbow III
Polarisation Rainbow
Halo I
Halo II
Sun Pillar
Sun through clouds
Crepuscular Rays


Sun Pillar

These images show the optical phenomenon of a sun pillar which often occurs in the arctic. Thereby different parameters of exposure were tested by the camera. Sun pillars are generated by the reflection of the sun light at pillar- or plate-like ice-crystals which are oriented while declining through the air. In the artic such crystals are formed also in clear cloudless air in wintertime. This can be recognized in all pictures shown here, except SunPillar1.jpg. Here Cirrus clouds caused the (weak) reflection. The crystals do not have to float strictly "rectified" so that the reflecting surface are all parallel aligned like facets of a mirror. Rather the declining crystals oscillate around their axis.
This effect is especially strong when the reflection occurs at the bottom surface with the sun being accordingly low. Then the observer sees the sun pillar standing above the sun. Within this geometry the sun pillar appears in the reddish, because the light scattering at air molecules and particles along the long optical path from the sun to the eye extinguishes the other colours more efficiently.

Since the sun pillars are caused by reflection at crystal surfaces (and not by refraction passing the crystals) this optical effect is also called "reflection halo" (see also Reflection Halo).
SunPillar2.jpg to SunPillar6.jpg presents several sun pillars above the already invisible sun right after sunset. Here the parhelions or fragments of the halos are so intense that they are also accompanied by sun pillars. Sun pillars often occur together with halos, when the ice crystals are similar and reasonably monodisperse. If different types of ice crystals exist together, sun pillars can be already observed under conditions which are not sufficient for halos.

Sun pillars can be also noticed when the sun is low above water surfaces. Then the reflections are caused by waves; or - as it was the case in Window.jpg - when the inclining light is scattered in forward direction by parallel scratches in the window glass.

SunPillar1.jpg to SunPillar6.jpg: R. Weigel, EUPLEX Field Campaign, Kiruna, Northern Sweden, March 2003

Window.jpg: S. Borrmann, Ingelheim, Germany, 14 May 2004