What is a Sun Pillar, or Light Pillar? – WEA



What is a Sun Pillar, or Light Pillar?

A Sun Pillar

Is a halo phenomenon of a vertical shaft of light extending upward or downward from the sun. Typically seen during sunrise or sunset, sun pillars form when sunlight reflects off the surfaces of ice crystals associated with thin, high-level clouds (e.g. cirrostratus clouds). The hexagonal plate-like ice crystals fall with a horizontal orientation, gently rocking from side to side as they fall. When the sun is low on the horizon, an area of brightness appears in the sky above (or below) the sun as sunlight is reflected off the surfaces of these tipped ice crystals. However, often only the upper pillar appears.

Sun pillars are seen best within a few minutes of sunrise or sunset. Initially the have about the same color and width as the sun, but sunpillars will gradually change their color from orange-white to red-orange. Sun pillars generally fade 20 to 60 minutes after sunset. Under favorable conditions, e.g. icy fog, sun pillars might stretch out up to 30° above the sun, while light streaks of 5° to 10° are most common.

On rare occasions, regarded with awe in more superstitious times, it may occur with part of the parhelic cycle to give the appearance of a cross centered on the Sun. The sun pillar is comparable with the light course, the setting sun produces on a water surface.

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Since they are caused by the interaction of light with ice crystals, light pillars belong to the family of halos. The crystals responsible for light pillars usually consist of flat, hexagonal plates, which tend to orient themselves more or less horizontally as they fall through the air. Their collective surfaces act as a giant mirror, which reflects the light source upwards and/or downwards into a virtual image. As the crystals are disturbed by turbulence, the angle of their surfaces deviates some degrees from the horizontal orientation, causing the reflection (i.e. the light pillar) to become elongated into a column. The larger the crystals, the more pronounced this effect becomes. More rarely, column-shaped crystals can cause light pillars as well. In very cold weather, the ice crystals can be suspended near the ground, in which case they are referred to as diamond dust.

Unlike a light beam, a light pillar is not physically located above or below the light source. Its appearance of a vertical column is an optical illusion, resulting from the collective reflection off the ice crystals, only those of which that appear to lie in a vertical line direct the light rays towards the observer (similar to the reflection of a light source in a body of water)




A light pillar

Is an atmospheric optical phenomenon in the form of a vertical band of light which appears to extend above and/or below a light source. The effect is created by the reflection of light from numerous tiny ice crystals suspended in the atmosphere or clouds. The light can come from the Sun (usually when it is near or even below the horizon) in which case the phenomenon is called a sun pillar or solar pillar. It can also come from the Moon or from terrestrial sources such as streetlights

Click on Each Image, for a Full Size Image









Since they are caused by the interaction of light with ice crystals, light pillars belong to the family of halos. The crystals responsible for light pillars usually consist of flat, hexagonal plates, which tend to orient themselves more or less horizontally as they fall through the air. Their collective surfaces act as a giant mirror, which reflects the light source upwards and/or downwards into a virtual image. As the crystals are disturbed by turbulence, the angle of their surfaces deviates some degrees from the horizontal orientation, causing the reflection (i.e. the light pillar) to become elongated into a column. The larger the crystals, the more pronounced this effect becomes. More rarely, column-shaped crystals can cause light pillars as well. In very cold weather, the ice crystals can be suspended near the ground, in which case they are referred to as diamond dust.

Unlike a light beam, a light pillar is not physically located above or below the light source. Its appearance of a vertical column is an optical illusion, resulting from the collective reflection off the ice crystals, only those of which that appear to lie in a vertical line direct the light rays towards the observer (similar to the reflection of a light source in a body of water).


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