Stories from Physics for 11-14 14-16
Scattering of light by molecules in the atmosphere alters the polarisation of light emitted from the sun. The average degree of polarisation of the sky is around 40% and is maximum at the zenith of the sky. The highest degree of polarisation occurs when the sun is just below the horizon. There are three points of zero polarisation in the sky, known as neutral points, named after the scientists who discovered them:
- Arago’s point (25° above the anti-solar direction)
- Babinet’s point (10-20° above the sun on a vertical circle passing through it)
- Brewster’s point (10-20° below the sun on the vertical circle passing through it).
G. P. Konnen, Polarized Light in Nature, Cambridge, Cambridge University Press, 1985, p. 32.
D. Clarke, Stellar Polarimetry, Weinheim, Wiley-VCH Verlag, 2010, p. 15.