![]() ![]() Ripples on the surface of the water reflect the light source in many directions, and those that happen to be aimed at the viewer, combine to form a bright line pointing toward the light source. This is similar to viewing a light source on a body of water. Nitrogen in the atmosphere is a selective scatterer and scatters shorter wavelengths of visible light (violet, blue and green) more efficiently than longer. Its appearance as a vertical line is an optical illusion, resulting from the collective reflection off the ice crystals but only those that are in the common vertical plane, direct the light rays towards the observer (See drawing). Unlike a light beam, a light pillar is not physically located above or below the light source. In very cold weather, the ice crystals can be suspended near the ground, in which case they are referred to as diamond dust. ![]() More rarely, column-shaped crystals can cause light pillars as well. The larger and more numerous the crystals, the more pronounced this effect becomes. 1 The word comes to English via the French (se) mirer, from the Latin mirari, meaning 'to look at, to wonder at'. ![]() Each flake acts as a tiny mirror which reflects light sources that are appropriately positioned below it (see drawing), and the presence of flakes at a spread of altitudes causes the reflection to be elongated vertically into a column. a A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. 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. Since they are caused by the interaction of light with ice crystals, light pillars belong to the family of halos. ![]()
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