A sun pillar can sometimes be seen above the sun when it is setting or rising. It is caused by reflection of light off the base of horizontally aligned plate ice crystals in the atmosphere. The extend of the pillar is usually only a few degrees. More rarely, it is as much as 20 degrees or more. Sun pillars are possible above and below the sun or moon; however, for earth-bound observers, the upper sun pillar is most common, while the lower pillar is more likely when you are in an airplane flying above a cloud of ice crystals. The upper and lower sun pillars at the sun can be present together with the parhelic circle and then form a giant cross in the sky.