View from space: Crepuscular rays

Have you seen crepuscular rays from the ground, fanning out from a sunset or sunrise? Now see them from space.

Astronauts in the Expedition 29 crew of the International Space Station (ISS) acquired this amazing image of crepuscular rays seen above India on October 18, 2011.

Crepuscular rays seen above India by astronauts in the International Space Station’s Expedition 29 crew on October 18, 2011. Image Credit: NASA

In this image, which was taken above India, the rays appear as dark straight lines running parallel from side to side. The sun was setting to the west (image left) on the Indian subcontinent, and cumulonimbus cloud towers provided the shadowing obstructions. The rays are being projected onto a layer of haze below the clouds.

This image from space was acquired on October 18, 2011, with a Nikon D2Xs digital camera using a 110 mm lens. NASA says the image has been cropped and enhanced to improve contrast. Lens artifacts were removed.

Have you seen crepuscular rays from the ground? They are those amazing sunrays that sometimes fan out from a sunset or sunrise – or even from a single cloud when the sun shines from behind it.

Crepuscular rays seen from Santa Clarita, California. Image taken September 30, 2011. Image Credit: Wikimedia Commons

From Earth, crepuscular rays do not look parallel. Instead, they appear to radiate outwards from the source of light. But this “fan-like” effect is an illusion, caused by the effects of distance and perspective. Crepuscular rays are actually parallel as the image from space shows.

Crepuscular means like twilight or dim. That’s a clue that this effect is normally seen before sunrise or just after sunset, when the sky is somewhat dark. The shadowed areas bounding the rays are typically formed by clouds or mountain tops that block the path of sunlight or moonlight. However, obstructions alone are not sufficient to create crepuscular rays. The light also must be scattered by airborne dust, aerosols, water droplets, or molecules of air, providing a visible contrast between shadowed and illuminated parts of the sky.

Bottom line: Astronauts in the International Space Station’s Expedition 29 crew acquired an amazing image of crepuscular rays seen above India on October 18, 2011.

Via NASA’s Earth Observatory

Sunrays before and after sunset

Deborah Byrd