Physics Photo of the Week

February 21, 2014

Shadow Color
Last weeks big snowstorm gave us a chance to compare the color of shadows.  We discussed why snow is "white" in last week's Physics Photo of the Week (link here).  However look carefully at the color of the shadows in the lower right.  They appear blue in spite of the snow being "white", whereas the sunlit portion of the snow is a creamy color.  Any white surface, such as a projection screen, or snow, reflects all the colors of the light that is impinging on it.  Where the snow is sunlit, it reflects the color of the early morning Sun.  In the shadows, there is no direct sunlight.  The source of the light for the shadows (they are not black) is the blue sky, thus the shadows in the snow on a sunny day are blue.

Pieces of the above picture are reproduced below to show the color contrast better.  The left portion is just a small portion of the shadow in the lower left while the portion of the picture on the right is a similar portion from the lower center of the photo.

Also notice all the colors in the full photo giving a "warm" appearance.  The "warmth" effect is due to the Sun having just risen.  The sunlight has a bit reddish tint because the sunlight travels through so much atmosphere.  More on that in a future Physics Photo of the Week.

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to

All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion.  These photos and discussions may be used for private individual use or educational use.  Any commercial use without written permission of the photoprovider is forbidden.

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