Sun pillar

Last updated on September 16, 2023

Sun Pillar: A Phenomenon of Light

Have you ever looked up at the sky and noticed a vertical column of light extending above or below the sun? This intriguing optical phenomenon is known as a sun pillar. Sun pillars are a captivating sight, often appearing as tall, shimmering beams of light that add an ethereal touch to the sky. In this article, we will delve into the science behind sun pillars, their formation, and the atmospheric conditions required for their occurrence.

What Causes a Sun Pillar?

A sun pillar is created when sunlight interacts with ice crystals in the atmosphere. These ice crystals can be found in high-altitude clouds, such as cirrostratus or altocumulus clouds. As sunlight passes through these hexagonal ice crystals, it undergoes a process called refraction. Refraction occurs when light bends as it passes from one medium to another, in this case from air to ice.

The Formation Process

When sunlight enters the ice crystal, it refracts and splits into different colors, similar to how light disperses in a prism. The individual rays of light then bounce off the internal surfaces of the crystal and exit in a parallel manner. This parallel alignment of light rays creates the illusion of a vertical column extending above or below the sun.

Atmospheric Conditions for Sun Pillar Formation

Several atmospheric conditions must be met for a sun pillar to form. Firstly, there must be a sufficient number of ice crystals present in the atmosphere. These crystals need to be of a specific shape and orientation to create the desired effect. Hexagonal plate-like ice crystals or column-shaped ones are particularly effective at producing sun pillars.

Additionally, the orientation of the ice crystals is crucial. The flat sides of the hexagonal crystals must be roughly parallel to the ground for the pillar to appear vertical. If the crystals are randomly oriented, the light will scatter in various directions, obscuring the pillar formation.

Colors and Variations

Sun pillars are often seen as white or pale yellow columns of light. However, under certain conditions, they can display a range of colors. This occurs when the ice crystals in the atmosphere act as tiny prisms, refracting the sunlight and creating a phenomenon known as a "mock sun." Mock suns, also called parhelia, can appear on either side of the sun and display vibrant colors similar to those seen in a rainbow.

Sun Pillar or Light Pillar?

It's worth noting that sun pillars are closely related to another optical phenomenon called light pillars. While both phenomena share similar characteristics, light pillars can occur at night when artificial lights, such as streetlights or car headlights, interact with ice crystals in the atmosphere. Light pillars can create mesmerizing vertical columns of light that resemble sun pillars, albeit with different light sources.

Capturing the Beauty

If you're fortunate enough to witness a sun pillar, it's undoubtedly a sight worth capturing. Photographing these ethereal columns of light can be a rewarding experience. To capture the full glory of a sun pillar, it's best to use a camera with manual settings. Adjusting the exposure and shutter speed can help bring out the details and colors of the phenomenon. Experimenting with different angles and compositions can also yield stunning results.

Conclusion

Sun pillars are a captivating natural phenomenon that adds an enchanting touch to our skies. Understanding the science behind their formation allows us to appreciate the intricate interplay between sunlight and ice crystals in the atmosphere. Whether you're an avid sky-watcher or simply enjoy the beauty of nature, keep an eye out for these mesmerizing vertical columns of light. You never know when you might catch a glimpse of a sun pillar and be awestruck by its ethereal beauty.

New Zealand Summer Pillar

Captured on February 18th 1997by Ian Cooper at his home at Palmerston, North Island.

©Ian Cooper, shown with permission.

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Reference Atmospheric Optics

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