Visual Measurements of the Polarization of the Solar Corona

Citation

Johnson, Josef Jerome (1935) Visual Measurements of the Polarization of the Solar Corona. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/FBFH-ER25. https://resolver.caltech.edu/CaltechETD:etd-09112007-075222

Abstract

Visual polarization measurements were made at the eclipse of February 14, 1934, with a modified Lyot-type polarimeter attached to a four-inch equatorially-mounted refractor. The objective was stopped down to 1 1/2 inches to reduce polarization effects the instrument. Distances from the moon's limb were measured by means of a cross-wire reticle in the focal plane of the eyepiece.

Five different points of the corona were investigated, all lying directly off the east limb of the sun and ranging in distance from the limb from 1 to 8.5 minutes of arc. The observed polarization rose rapidly from 17% at 1' to 26% at 4', remaining sensibly constant from 4' outward.

These values are considerably higher than those previously obtained by visual methods, but are lower than the values obtained photographically. Subject to confirmation at a future eclipse, these values will constitute important evidence in favor of Schwarzschild's theory that a large part of the light of the corona is due to the scattering of photospheric light by free electrons.

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