Earth from Space – Crepuscular rays

Crepuscular rays seen from space

Rays of light and dark appear to emanate from clouds in this image taken by an astronaut aboard the International Space Station. They are called crepuscular rays.

CREPUSCULAR RAYS OVER THE OCEAN near India are featured in this image photographed by an Expedition 29 crewmember on the International Space Station.

The sight of shafts of light, beaming down from the heavens through a layer of clouds, has provided many an artist, scientist, and philosopher with inspiration throughout the centuries.

Atmospheric scientists refer to this phenomenon as “crepuscular rays“, referring to the typical observation times of either sunrise or sunset.

Shadowed areas bounding the rays are formed by obstructions in the solar (or lunar) illumination pathway such as clouds or mountaintops; however this alone is not sufficient to create the phenomenon. The light must also be scattered—by airborne dust, aerosols, water droplets, or molecules of the air itself—to provide the visible contrast between the shadowed and illuminated parts of the sky.

Crepuscular rays seen from the ground.

A ground-based image of crepuscular rays shows them appear to radiate from a central point, a perspective effect. The orbital image above shows them in fact to be parallel.

When observed from the ground, crepuscular rays appear to radiate outwards from the source of illumination due to the effects of distance and perspective; however the rays are actually parallel.

This photograph from the Space Station provides an unusual viewing perspective from above the rays. The sun was setting to the west on the Indian subcontinent at the time the image was taken, and cumulonimbus cloud towers provide the shadowing obstructions.

The rays are being projected onto a layer of haze below the cloud towers. The image clearly illustrates the true parallel nature of the crepuscular rays.

See the full-size image here.

Orbital image courtesy NASA. Ground-based image of crepuscular rays from Wikipedia, courtesy Chevy111, posted under the Creative Commons Attribution-ShareAlike 3.0 License.

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