Physics Photo of the Week
April
25, 2008
Hummingbird Iridescence
In mid
May, 2007, our door was open to enjoy the nice weather, but the screen
wasn't up yet. This hummingbird flew right into the house.
Once birds get inside a house, they have a terrible time finding the
way out. They keep trying the upper windows that are
closed. They refuse to fly low enough to go through the doorway.
After several minutes of vainly flying around beating against
the windows, the bird eventually rams itself into a window and stuns
itself - falling to the floor. I was able to pick it up and carry
it outside and it eventually regained its composure. While it was
recovering I got some close-up photos. Note the coppery appearance of
the bird's back.
The pigmented color of the bird's feathers are brown, but the
iridescence gives it a coppery glow. The iridesence is caused by
diffraction of light by the extremely fine structure in the
feathers. Each feather acts as a diffraction grating - similar to
the very fine arrays of pits in a CD disk. At different angles to
the sunlight, different wavelengths of light are diffracted toward the
observer.
The hummingbird soon gathered its strength
enough to fly away and continue its remarkable flight -
beating its wings about 15 times a second to browse its nourishment
from the garden flowers.
Diffraction gratings are used extensively in many sciences to analyze
the wavelengths of light. This helps to identify chemicals and
the
materials that exist in stars. Spectra produced by simple
discharge lamps and diffraction gratings have been shown in a previous
Physics Photo of the Week (April
16, 2004). It is amazing that nature provides diffraction
gratings very similar to expensive gratings used in analytical
instruments!
Physics
Photo of the
Week is
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature an 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 dcollins@warren-wilson.edu.
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.
Click
here to see the Physics Photo
of
the Week Archive.
Observers are invited to submit
digital photos to:
