Sky brightness and polarization during the 1973 african eclipse.

The absolute intensity, color, and polarization of the sky were measured during the eclipse of 30 June 1973 in Northern Kenya. Zenith sky radiance during totality decreased by a factor of 10(4) from the normal day sky value. The distribution of sky intensity with angle on the celestial hemisphere was approximately symmetrical about the local zenith, with this point having the minimum intensity value. The spectral distribution of zenithal diffuse skylight shifted toward the blue during totality, but the horizon reddened. The polarization ratio P decreased from a normal day value of 0.45 to 0.04. There is evidence that the distribution of polarization ratio is strongly affected by variations in surface albedo. The major results are compatible with predictions based on a radiative transfer model that considers double-scattering processes only.