Day sky brightness and polarization during the total solar eclipse of 7 march 1970.

Zenith sky brightness at totality was observed to be about four orders of magnitude lower than that for a normal day sky. The spectral distributions in terms of an effective blackbody temperature for the range 4100-8000 A were 5000 K, 9000 K, and 11,000 K for the twilight, control day sky, and totality, respectively, indicating a shift toward the shorter wavelength at totality. The polarization measured in the sun's vertical plane 90 degrees away from the sun was 4% and 0.6% at 4750 A and 6000 A, respectively. Both colors showed a change in the plane of polarization of about 50 degrees at the time of totality. From the change in the plane of polarization it is estimated from the primary component reduced by about an order of magnitude at totality of the eclipse.