Lights radiating from the zenith
Pillar image index Lights radiating from the zenith. Joel Bavais (site) saw these strange luminous shapes in the sky from near the centre of the city of Ath in Belgium on 20th November '06. The air was very cold and shortly afterwards an ice fog descended and obliterated the lights. Image ©2006 Joel Bavais, shown with permission.

The lights are a form of light pillar and are produced by flat plate shaped ice crystals in layers of ice fog above the city. Why do the lines of light converge on the zenith? The diagram at right shows rays from just one nearby city light shining upwards onto crystals at different heights. Only crystals on a column roughly midway between the light and the observer give a reflection into the eye because the small crystal mirrors are nearly horizontal and the incident and reflected rays must make equal angles to the crystal faces. The higher the crystal, the more closely does the reflected ray come from the direction of the zenith. Therefore, when there is a cloud of crystals, their reflections appear as a line of light that points directly overhead, the zenith. Why are the lines broken? That night there must have been several layers of crystals at different heights over the city with zones in between them either without ice crystals or with crystals that were not specially oriented.