On a cold and sunny winter night, you may catch a glimpse of nature’s unique Christmas light show. The beam of light is an illusion in which a thin, vertical beam of light strikes the sky above or below an artificial or natural light source. These beams are members of the "halo" family, and are also called sun pillars, moon pillars, moon pillars, and luminous pillars.
Lamppost in North Bay, Ontario. Photo: Timmy Joe Elzinga
People have been studying halo since the time of Aristotle. Many cultures have watched these beautiful displays with suspicion and fear, believing that they are signs that a storm is coming—sometimes it does. Others use it as a symbol of purity and holiness in religious portraits. What is impressive is that they are just light tricks.
The formation of halo requires two key components: ice crystals and a light source. However, the way the two interact is very different. The beam of light is often mistaken for an aurora and confused with another optical phenomenon called the sun dog (also known as the sun dog or the simulated sun). Sundogs occur when light hits ice crystals and refracts the light at an angle of exactly 22°, forming a ring around the sun. The beam of light forms different forms by reflection rather than refraction.
Sundog on Ellesmere Island. Photo: Jerry Kobarenko
The beam of light mainly appears in the northern region, but also in the desert where the night temperature drops to close to freezing. The tiny ice crystals in the air slowly drift downwards until they are below or directly above the horizon. Each hexagonal crystal becomes a mirror, reflecting the light from the sun, moon or street lamp directly above. The reflection looks like an elongated beam of light.
The larger and thicker the ice crystal, the larger and stronger the beam of light. The color of the light beam depends on the color temperature of the light source. The air must be calm, because the wind will destroy the image.
The working principle of the lamp post. Photo: Ashley Brauweiler/Shutterstock
Meteorologists have linked beams of light and halos to the existence of cirrostratus and cirrus clouds. These are very thin, hazy high-altitude clouds composed entirely of ice crystals. Most halos are related to these clouds, but sometimes low clouds or even ground clouds create the same conditions for the formation of pillars.
Diamond powder in the beam of light. Photo: w.aoki/Shutterstock
Finally, diamond dust is a low-level mist that appears on a cold winter morning. When the temperature is at least 20°C below the freezing point and a temperature inversion occurs, diamond dust is formed. This is when the cooler air near the ground interacts with the warmer air above it. Water vapor turns into ice crystals. When the sun shines on the crystal, the air seems to be covered with sparkling little diamonds.
Kristine De Abreu is a writer (and occasionally a photographer) living in sunny Trinidad and Tobago. After receiving a bachelor's degree in English and History from the University of Leicester, she has been engaged in a full-time writing career, exploring multiple fields before starting to travel and explore. While studying for an additional diploma in travel journalism at the British School of Journalism, she started writing for ExWeb. Currently, she works as an editorial assistant for a travel magazine in Trinidad and is also the strange wonder woman of ExWeb, reporting on the natural wonders of the world and general stories about exploring the world. Although she is not a climber (yet!), she hikes in the jungle, is known for making friends with iguanas, and quotes the Lord of the Rings trilogy from beginning to end.
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