Polarization of the Solar Corona in the Total Eclipses of 1932 and 1934

Abstract

view Abstract Citations (8) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Polarization of the Solar Corona in the Total Eclipses of 1932 and 1934 Cohn, Willi M. Abstract Polarigraphs of 35k-inch and ôo-inch focal lengths, equipped with Wollaston prisms and Wratten Mters, were used. Intensity marks were printed on each coronal plate. The plates were measured with the Hartmann microphotometer of the Lick Observa- tory and the Zeiss microphotometer of the physics department of the University of California. The polarization was determined as a function of the distance from the sun's limb and as a function of the wave length. The influence of skylight on the polarization of the corona was eliminated in the reduction. The skylight close to the corona was found to be unpolarized in the violet, blue, and red spectral regions investigated. The shape of the coronal polarization curves for short and long wave lengths is different. The polarization in the integrated light, in the blue, and in the red increases steadily from the sun's limb toward the outer corona, whereas it reaches maxima in the violet and green and then decreases again. The polarization for short wave lengths is higher than that for long wave lengths in the inner corona; this ratio is reversed for distances of >4 5 from the limb; the polarization is independent of the wave length at 4 5, resulting in the intersection of the polarization curves for short and long wave lengths at 4 5. The polarization at short wave lengths is, for a certain distance from the limb, smaller at the poles than at the equator. The difference in polarization be- tween the polar and equatorial corona is less at long than at short wave lengths. The influence of prominences on the polarization of the corona was investigated. The polarization values of the corona are greatly depressed close to strong prominences, and the entire polarization curve seems shifted to a greater distance from the limb. A rota- tion of the plane of polarization by some prominences was observed. The polarization of a well-defined streamer was determined in 1932. The polarization curves at short wave lengths seem shifted to greater distances from the limb, resulting in smaller polari- zation values than in corresponding parts of the corona. The red curve agrees with the coronal values. The plane of polarization of the corona is, as a rule, radial; devia- tions from radial polarization occur in several cases and are explained by the greater amount of polarization at the equator than at the poles and by the difference in bright- ness of different parts of the corona. Visual determinations of the polarization were carried out ill 1932 in integrated light and in the red. Conclusions are drawn with regard to the distribution of particle sizes in the corona. The average particle size was found to increase from close to the limb toward the outer corona. The average diameter of a particle close to the limb amounts to less than 100 m~, and beyond 4~5, to less than 170 mji. The appearance of sharp Fraunhofer lines 5' from the limb is explained by reflection and diffraction of sunlight of short wave length by particles which are large compared with short wave lengths but are small compared with long wave lengths. The emission proper of the 1934 corona was computed as a function of the distance from the limb and for the spectral regions investigated. The emission of the corona de- creases, at all wave lengths, from the limb toward the middle corona. The emissions in the violet, blue, and green coincide very closely. The coronal emission at long wave lengths differs from that at short wave lengths. The emission proper of the corona close to the limb is relatively greater at short than at long wave lengths, this ratio being reversed farther away from the limb, indicating a coronal radiation of gradually de- 28 Publication: The Astrophysical Journal Pub Date: April 1938 DOI: 10.1086/143927 Bibcode: 1938ApJ....87..284C full text sources ADS |