Physics Photo of the Week

April 9, 2009

Irridescent Turkey
This handsome wild turkey lived in our neighborhood all winter.  His feathers show a shimmery irridescence when the lighting is right.  The irridiscence, or displaying many colors at once, is caused by the diffraction of light by the fine structure in the feathers.  Bird feathers often show irridescence.  To show the irridescence, the feathers must contain structures (ridges, microhooks, etc) that are regularly spaced and very close together (several hundred ridges per mm).  These features actually become a diffraction grating.  In certain directions the light of a particular color is reflected more than light of other colors giving the appearance of a rainbow color that changes with the angle. 

Today's photo features the irridescence in the feathers of one of the largest North American birds.  Physics Photo of the Week featured irridescence on one of the smallest North American birds - a hummingbird - on PPOW for April 25, 2008.

The photo at left is a close-up of the turkey's wing feathers.  Notice the almost metallic sheen to the feathers.  Also notice that some of the feathers in the upper left (about 1/3 from the top left) are bluish while the feathers in te center are golden.  The bluish feathers will appear golden when viewed face-on.  The color that is reflected depends critically on the angles of both the light and the viewing.

Compact disks are a prime everyday example of diffraction.  The thousands of tiny pits or holes representing the information and tracks in the CD diffract the light so that different colors are viewed from different angles.  Diffraction gratings are also very important scientifically.  They are used to separate light into spectra - an important analytical tool for astronomy, physics, chemistry, and biology.

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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