Today's Image

Cloud shadow

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November 20, 2015

View larger. | Photo by Asthadi Setyawan in Malang, East Java, Indonesia. — View larger. | Photo by Asthadi Setyawan in Indonesia.

Asthadi Setyawan in Malang, East Java, Indonesia posted this photo at EarthSky Photo on G+. What you see here is the shadow of a cloud. The great sky optics expert Les Cowley – of the website Atmospheric Optics – calls them the inverse of crepuscular rays and notes they can produce dramatic effects.

We asked Les why it appears that this shadow is on the wrong side of the cloud. It looks from the photo as if the sun and the shadow are both behind the cloud. He told EarthSky:

It only looks that way. The shadow is closer to the camera than the cloud. Rays from the sun 93 million miles [150 million km] away are (nearly) parallel and always downward pointing. The shadows can be through misty or hazy air, or, sometimes, they’re cast on a lower thin layer of cloud that is otherwise invisible.

Check Les’ website for diagrams that explain the two cases here and here.

Thank you, Asthadi, and thank you, Les!

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November 20, 2015

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Today's Image

Deborah Byrd

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About the Author:

Deborah Byrd (asteroid 3505 Byrd) helps edit EarthSky.org and is a frequent host of EarthSky videos. Deborah created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named in her honor in 1990, a Public Service Award from the National Science Board in 2003, and the Education Prize from the American Astronomical Society in 2020. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.