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Light pillar

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A light pillar is a striking atmospheric optical phenomenon.

Light Pillars and Diamond Dust in London Ontario Canada
Light Pillars and Diamond Dust in London Ontario Canada

It appears as a vertical beam of light. This beam can extend above or below a light source. These pillars are part of the halo family of light effects. They are not physical beams of light traveling through space. Instead, they are an optical illusion. This illusion occurs when light interacts with ice crystals in the atmosphere.

Light Pillars Scheme
Light Pillars Scheme

Understanding these pillars helps us learn how light and ice work together.

The formation of a light pillar depends on specific ice crystals. These crystals are usually flat, hexagonal plates. As these plates fall through the air, they tend to orient themselves horizontally. Each individual flake acts like a tiny mirror. These mirrors reflect light from a source located below them. Because many flakes exist at many different altitudes, the reflections appear elongated. This creates the appearance of a tall, vertical column of light.

Light Pillars Scheme
Light Pillars Scheme

The effect becomes more pronounced if the crystals are large or numerous.

There are different types of light pillars based on their source. If the light comes from the sun, it is called a sun pillar or a solar pillar. This often happens when the sun is near or below the horizon.

Sun pillar and kitesurfers
Sun pillar and kitesurfers

The moon can also serve as a light source for these pillars. Even terrestrial sources can create the effect. These include streetlights or even erupting volcanoes. The specific name changes depending on what is providing the light.

Ice crystals can exist in different parts of the atmosphere. Some crystals are suspended in high-altitude clouds. These include cirrus clouds or cirrostratus clouds. In other cases, the crystals are suspended much closer to the ground. This occurs during very cold weather. When crystals stay near the ground, they are referred to as diamond dust.

Light Pillars and Diamond Dust in London Ontario Canada
Light Pillars and Diamond Dust in London Ontario Canada

Both high clouds and diamond dust can produce these beautiful light columns.

It is important to understand that the pillar is an illusion. A light pillar is not physically located above or below the source. It is a result of collective reflection. Only the crystals in a specific vertical plane reflect light toward the observer. This process is very similar to seeing light on a body of water.

Sun pillar and kitesurfers
Sun pillar and kitesurfers

Ripples on water reflect light in many different directions. The ripples that are aimed directly at the viewer combine to form a bright line. This line points back toward the light source. The ice crystals perform a similar task in the sky.

Scientists categorize these events within the broader study of atmospheric optics. Light pillars belong to the same family as other phenomena like sun dogs. They also relate to things called crepuscular rays. While they look similar, the mechanics of reflection are unique to the crystals. The shape of the crystals matters deeply. While hexagonal plates are most common, column-shaped crystals can also cause light pillars. This shows how the geometry of tiny objects can change what we see in the sky.

Light pillars provide a way to visualize the presence of ice in our air. They show us how light travels and reflects off microscopic surfaces. By observing the brightness and height of a pillar, we can learn about the crystals. More and larger crystals create a more intense visual effect. This connection between light, temperature, and crystal shape makes the phenomenon a key part of studying our atmosphere.

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File:Light Pillars and Diamond Dust in London Ontario Canada.jpg
Light Pillars and Diamond Dust in London...
File:Sun pillar and kitesurfers.jpg
Sun pillar and kitesurfers.jpg
File:Light Pillars Scheme.svg
Light Pillars Scheme.svg
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