Light Pillars - Lights radiating from the zenith

Last updated on September 16, 2023

Light Pillars: Lights Radiating from the Zenith

Have you ever witnessed a captivating phenomenon in the night sky where lights seem to radiate from the zenith? These mesmerizing luminous shapes, known as light pillars, can be quite a sight to behold. They occur when flat plate-shaped ice crystals form in layers of ice fog above a city, creating a breathtaking display of light. In this article, we will delve deeper into the science behind these ethereal pillars and explore why the lines of light converge on the zenith.

The Convergence of Light

To understand why the lines of light converge on the zenith, let's examine the interaction between the light source and the ice crystals. Imagine rays of light emanating from a nearby city light and shining upwards onto crystals at different heights. The key factor here is that only crystals on a column approximately midway between the light and the observer reflect light into the eye. This is because the small crystal mirrors are nearly horizontal, requiring the incident and reflected rays to make equal angles to the crystal faces.

As the crystals rise higher, the angle at which the reflected ray approaches the observer becomes closer to the direction of the zenith. Consequently, when a cloud of crystals is present, their reflections manifest as a line of light that points directly overhead, towards the zenith.

The Broken Lines

You may have noticed that the lines of light appear broken rather than forming a continuous pillar. This is due to the presence of several layers of crystals at different heights above the city. These layers create zones in between them that either lack ice crystals or contain crystals that are not specially oriented. As a result, the lines of light become fragmented, adding an intriguing aspect to the overall spectacle.

The Beauty of Light Pillars

Light pillars have captivated observers for centuries with their enchanting beauty. These atmospheric optical phenomena often occur in cold weather conditions when ice fog forms above urban areas. The combination of artificial city lights and the presence of ice crystals provides the perfect canvas for this awe-inspiring display. As the light interacts with the ice crystals, it scatters and reflects, creating a vertical column of shimmering light that extends towards the heavens.

Other Factors Influencing Light Pillars

While the convergence of light and the presence of ice crystals are the primary factors contributing to the formation of light pillars, other variables can influence their appearance. These include:

• Temperature: Light pillars tend to occur in extremely cold temperatures, which facilitate the formation of ice fog and ice crystals.
• Humidity: Higher humidity levels can increase the likelihood of ice fog formation, enhancing the conditions for light pillars to occur.
• Atmospheric Stability: A stable atmosphere helps maintain the presence of ice fog and ice crystals, increasing the chances of witnessing light pillars.

The Allure of Atmospheric Optics

Atmospheric optics never cease to amaze us with its myriad of captivating phenomena. From rainbows and halos to light pillars and beyond, these natural spectacles remind us of the wonders that surround us. Light pillars, in particular, offer a unique and enchanting display that leaves viewers in awe of nature's artistic prowess.

Next time you find yourself gazing at the night sky and witness lights radiating from the zenith, take a moment to appreciate the beauty and science behind these ethereal light pillars. They serve as a reminder of the intricate dance between light and ice crystals, showcasing nature's ability to create stunning displays that captivate our imaginations.

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.

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Reference Atmospheric Optics

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