Earth Science Image of the day

Sundog Pair Over Central Germany - October 23, 2019

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Photographer: Rocco Lico 
Summary Authors: Rocco Lico; Jim Foster

These attention-getting sundogs, also known as parhelia, were photographed while flying between Munich to Cologne, Germany on October 3, 2019. We were at an altitude of approximately 26,000 ft (7,924 m).

Sundogs are colored patches of light either or one or both sides of the Sun at a distance of about 22 degrees. They occur at the same solar altitude of the Sun, whether the Sun is near the horizon or higher up in the sky. Refraction of sunlight by small hexagonal ice crystals (~10-30 micrometer), typically composing cirrus type clouds, is responsible for their formation. However, the faces of these plate-shaped crystals must be nearly horizontal. Sunlight enters one of the crystal's 6 side faces and exits through another side face that’s inclined 60 degrees to where it first entered. These two refractions (when entering and exiting the crystal) deviate the initial ray of light by approximately 22 degrees. Because red light is bent less than blue light, the sunward edges of sundogs always take on reddish hues.

Note the stratocumulus cloud deck below the plane and the contrail at upper left.

Photo Details: Samsung Galaxy S6 smartphone camera; using the 16-megapixel Sony Exmor RS IMX240 sensor; f/1.9 focal length; 4.30 mm; ISO 50; 1/2528 second exposure time.

 EPOD is a service of NASA's Earth Science Division and the EOS Project Science Office (at Goddard Space Flight Center)
and the Universities Space Research Association.

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