Polarization fingerprints in the clear blue sky

Michael Berry

Physics Department, Bristol University (Wolf prize laureate)

Daylight is polarized, the strength being greatest at points in the sky at right angles to the sun, 
and zero at four points: above and below the sun and anti-sun. The zero-polarization points 
are 'fingerprint' singularities, around which the polarization direction makes a half-turn. 
Using elementary singularity theory, the polarization pattern across the whole sky can be 
described in a way that fits recent observations with an accuracy comparable to that of 
conventional elaborate multiple-scattering calculations. This recent work is a contribution
 to a story that started in 1817 and has been central to our understanding of polarized light.