Physics Photo of the Week
this Wednesday, May 5, 2010, we had a sunset on a mostly clear day with
a few scattered clouds. The clouds cast their shadows onto the
air beyond. The shadows and light beams from the Sun are clearly
visible as scattered light from the air molecules and dust in the
air. There was not much dust nor haze - the air was about as
These rays are quite common. They are called "crepuscular rays"
because they occur most frequently near sunrise and sunset - the
transition between daylight and night. "Crepuscular animals" like
deer are active at twilight as opposed to nocturnal and diurnal animals.
Crepuscular rays appear to radiate outward from the position of the Sun.
divergence is just an optical illusion. The rays and
shadows of the clouds are all parallel because the Sun is very far
away. The appearance of the divergence (or convergence towards
the Sun) is analogous to the perspective convergence of parallel
railroad tracks. See the PPOW
15, 2006 writen by Kopano Mmalane during her first year at
WWC. (Kopano is graduating next week. Congratulations!)
Photo of the
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 firstname.lastname@example.org.
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.
the Physics Photo
the Week Archive.
Observers are invited to submit
digital photos to: