A light pillar is an optical phenomenon where a column of light can be seen emanating from a light source. If the light comes from the Sun, the phenomenon is called a sun pillar. Light pillars can also be caused by the Moon or streetlights.
This image of a sun pillar was captured by ESA-sponsored medical doctor Hannes Hagson. Image credit: ESA / IPEV / PNRA / H. Hagson.
Light pillars belong to the family of optical phenomena known as halos and are caused by the interaction of light with ice crystals.
The crystals consist of flat, hexagonal plates, which tend to orient themselves more or less horizontally as they fall through the air.
Each flake acts as a tiny mirror which reflects light sources which are appropriately positioned below it.
The presence of flakes at a spread of altitudes causes the reflection to be elongated vertically into a column.
The larger and more numerous the crystals, the more pronounced this effect becomes.
“Known as a sun pillar, this optical phenomenon occurs when sunlight is reflected from tiny ice crystals suspended in the atmosphere,” ESA researchers explained.
“Though it appears to reach from the Sun itself, the pillar is not physically located above or below the Sun.”
“But it’s not just the Sun that creates this optical illusion,” they added.
“Moonlight, and even streetlights, can create the same effect in icy conditions, in which case it is known more generally as a light pillar.”
This image of a sun pillar was taken by Dr. Hannes Hagson, an ESA-sponsored medical doctor from Sweden spending 12 months at Concordia research station in Antarctica.
“Concordia station is located on the Antarctic plateau known as Dome C, 3,233 m above sea level,” the scientists said.
“Dr. Hannes is spending a year at the remote base to facilitate biomedical experiments on both his 11 crew mates and himself, all in the name of science and space exploration.”
“Over the course of a year, Dr. Hannes has been sampling and recording the effects of lack of sunlight (during four-month winter) and less oxygen (due to the altitude) on himself and his crew for researchers developing countermeasures to altered motor skills, memory, sleep patterns and moods.”
