Editing Polarization (waves) (section)

=== Sky polarization and photography ===
{{Further|Polarizing filter (Photography)}}
[[File:CircularPolarizer.jpg|right|thumb|upright=1.5|The effects of a [[polarizing filter (photography)|polarizing filter]] (right image) on the sky in a photograph]]

Polarization is observed in the light of the [[Sky#During daytime|sky]], as this is due to sunlight [[light scattering by particles|scattered]] by [[aerosols]] as it passes through [[Earth's atmosphere]]. The [[Rayleigh scattering|scattered]] light produces the brightness and color in clear skies. This partial polarization of scattered light can be used to darken the sky in photographs, increasing the contrast. This effect is most strongly observed at points on the sky making a 90° angle to the Sun. Polarizing filters use these effects to optimize the results of photographing scenes in which reflection or scattering by the sky is involved.<ref name=Hecht2002>{{cite book|last=Hecht|first=Eugene|title=Optics|date=2002| location=United States of America|publisher=Addison Wesley| edition=4th|isbn=0-8053-8566-5}}</ref>{{rp|346–347}}<ref name=Bekefi>{{cite book|last1=Bekefi|first1=George|last2=Barrett|first2=Alan|title=Electromagnetic Vibrations, Waves, and Radiation|url=https://archive.org/details/electromagneticv0000beke|url-access=registration|publisher=MIT Press|location=USA|isbn=0-262-52047-8|date=1977}}</ref>{{rp|495–499}}

[[File:cmglee_London_Embassy_Gardens_pool_polariser.jpg|thumb|upright|Colored fringes in the [[Sky Pool, London|Embassy Gardens Sky Pool]] when viewed through a polarizer, due to stress-induced birefringence in the skylight]]
Sky polarization has been used for orientation in navigation. The [[August Herman Pfund|Pfund sky compass]] was used in the 1950s when navigating near the poles of the [[Earth's magnetic field]] when neither the [[sun]] nor [[star]]s were visible (e.g., under daytime [[cloud]] or [[twilight]]). It has been suggested, controversially, that the [[Viking]]s exploited a similar device (the "[[sunstone (medieval)|sunstone]]") in their extensive expeditions across the [[North Atlantic]] in the 9th–11th centuries, before the arrival of the [[magnetic compass]] from Asia to Europe in the 12th century. Related to the sky compass is the "[[polar clock]]", invented by [[Charles Wheatstone]] in the late 19th century.<ref name="Pye2001">{{cite book|author=J. David Pye|title=Polarised Light in Science and Nature|date=13 February 2001|publisher=CRC Press|isbn=978-0-7503-0673-7}}</ref>{{rp|67–69}}