Physics Photo of the Week

April 20, 2012

Almost two years ago (May 16, 2010) I had a chance to capture a rainbow happening with a time lapse.  The rain had passed so I didn't have to worry about getting the camera wet.  This was a typical afternoon rain shower typical of the season in the mid-afternoon.  By studying the animation, we can see the distant rain squall passing along the Swannanoa Valley and more rain appearing in the sunlight and creating the familiar rainbow.  Notice not only is the rain squall traveling to the left and lengthening the bow, but the rainbow is also slowly rising in the sky reflecting the passage of the Sun lower in the sky as time progresses.  The Sun is behind the camera (always for a rainbow).  With the Sun becoming lower in the sky the rainbow is rising in the opposite direction - keeping the same constant angle between the Sun's direction and the arc of the rainbow.  The physics of the rainbow is explained in other PPOW's: Oct. 29, 2010 and April 4, 2008;
A related droplet phenomenon is shown in a Spider's rainbow.

At right is a full-frame photograph of this rainbow showing the storm clouds that produced the spotty rain.

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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Observers are invited to submit digital photos to: