What is Double Sun halo?

About Double Sun halo: 

• It is a rare optical phenomenon where two concentric rings appear around the sun.
• This occurs when sunlight is refracted through ice crystals suspended in cirrus clouds, creating this dazzling visual effect.
• It is a variation of the more common 22-degree halo, where a bright ring encircles the sun. 
• In this case, two halos are visible – an inner halo with a radius of approximately 22 degrees and an outer halo with a radius of around 46 degrees from the sun’s center.
• Formation:
  • The formation of a double sun halo is a result of the unique shape and orientation of the ice crystals in the cirrus clouds. These crystals, typically hexagonal in shape, act as natural prisms, refracting and reflecting the sunlight in specific angles.
  • When the ice crystals are randomly oriented, the refracted sunlight creates the inner 22-degree halo. However, if the crystals are aligned horizontally, with their flat faces parallel to the ground, an additional refraction occurs, resulting in the outer 46-degree halo.
  • This precise alignment of the ice crystals is rare, making the double sun halo a relatively uncommon sight, especially in regions like Ladakh, where the atmospheric conditions are ideal for such phenomena.

Q1: What are Cirrus Clouds?

Cirrus Clouds are delicate, feathery clouds that are made mostly of ice crystals. They are thin and wispy in appearance, often appearing as delicate, high-altitude filaments or strands.

Source: Rare double Sun halo seen in Leh: What is this rare phenomenon?

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