Cloud of the Day – Pillar
The pillar is an optical phenomenon where a light source, the Sun or the Moon or a streetlight, eg, is accompanied by a vertical column of light. Depending on the position of the light relative to the viewer, the pillar can be above or below the source, or both. Pillars are related to halos, being caused by light interacting with ice crystals, but can appear alone.
While halos are produced by the refraction of light through ice crystals, pillars form when the light reflects off of them. Because the ice crystals are all in different orientations as they sift through the air, the light source is reflected to you from different altitudes, elongating the reflection. Usually the type of ice crystal involved is the flat, hexagonal plate.
The pillar is not associated with any type of weather, only with the presence of ice crystals between the viewer and the light source.