Rainbow Polarization

March 02, 2006


Provided and copyright by: David Lien, Planetary Science Institute
Summary authors & editors: David Lien

These two images of a late afternoon rainbow in Tuscon, Arizona were taken within 20 seconds of each other (taken in July of 2005). The difference? Each picture was taken through a polarizing filter which was rotated 90 degrees between the two photographs. The light waves that are ultimately redirected to create the rainbow are reflected at the back of the raindrop, and the angle of redirection is very close to Brewster's angle for a water-air interface. Light reflecting off of a surface at Brewster's angle is 100% polarized. Since the sunlight resulting in a rainbow reflects off the back of a drop over a small range of angles, rainbows are not 100% polarized (~95% polarization is typical). Note that these images also show faint anti-crepuscular rays created by storm clouds along the western horizon.

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