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Tuesday, 19 November 2013

Sun Pillars

    Sometimes above the sun (or occasionally below), you may see a vertical beam of light stemming from the sun.
Sun Pillar
     This vertical light is an optical phenomenon called a light pillar, sun pillar, or sun dog.
     The most common occurrences of light pillars are avove the sun when it is close to the horizon, although it can also occur with other natural light sources such as planets or various artificial light sources.
     Certain conditions are necessary for a sun pillar to appear because the appearance of a light pillar is created by the reflection of light on horizontal ice crystals in the Earth's atmosphere. When the light reflects off the bottom of the horizontal ice crystals down to the eye or by total internal reflection (the same concept as bike reflectors), it creates the appearance of an upper light pillar (above the sun). This is why it is more common to see a light pillar when the sun is closer to the horizon. When it reflects off the top of a lower ice crystal and up to the eye, you would see a lower light pillar (under the sun).
     The visual result is a towering vertical line of light extending through the sky, of the same colour as the light source.


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