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The Sun's crystal horns

If conditions are right, look for this rare optical event.

The Northern Hemisphere’s winter can bring an abundance of microscopic ice crystals to the skies, and under the right conditions, these crystals interact with sunlight to create colorful atmospheric phenomena.

This month’s column was inspired by one such beautiful display captured above the Grand Canyon by Todd Smathers of Pleasanton, California. It includes long crystal horns and an uncommon arc of light first documented in 1820 by English naval officer and Arctic explorer Sir William Edward Parry while searching for the Northwest Passage.

The foundation

All the features captured by Smathers are tangential to, or near, the so-called 22° halo — a ring around the Sun with a radius of 22°. It’s the most common of all atmospheric displays created by ice crystals.

This usually sharp ring of orange and blue light appears when a gauze of thin cirrus clouds covers the sky. These clouds contain countless “pencil” crystals (long or columnar ice crystals shaped like hexagonal pencils) aligned with their long axes nearly horizontal. Their hexagonal shapes act like prisms, refracting and reflecting light.

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