Halo and Space Needle

May 18, 2004


Provided by: Annie Mejia; Joe Pirelli
Summary authors & editors: Jim Foster; Joe Pirelli

The photo above showing a fine example of a 22 degree solar halo was taken on March 28, 2004 in Seattle, Washington. The Space Needle was used to shield the camera from the Sun. Halos can occur if hexagonal (plate or column-shaped) ice crystals in cirrus-type clouds are more or less randomly oriented. In this case, the cirrus clouds are very faint. Sunlight enters one side of a crystal, is refracted, and then exits the opposite side, where it is again refracted by the same amount and in the same direction as the original refraction.

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