A Comparison of the Intensities of Infra-red and Violet Radiation from the Solar Corona at the Eclipse of 1952 February 25

Abstract

Measurements made in Khartoum at the total solar eclipse of 1952 February 25 show a considerable excess of infra-red radiation in the solar corona at 2.5 R_ʘ from the solar centre. The ratio $$\frac{I(1.9\mu,\,2.5{R}_{\odot})}{I(0.43\mu,\,2.5{R}_{\odot})}/\frac{I(1.9\mu,\,1.5{R}_{\odot})}{I(0.43\mu,\,1.5{R}_{\odot})}$$ equals 2.17, where I ( p , q ) is the intensity of the corona at the wave-length p and distance q from the Sun. The measurements were made with a 20-in. mirror of 45 in. focal length, using a lead sulphide cell and a photomultiplier. It is shown that the infra-red excess supports the current theory of an F-corona caused by diffraction of sunlight by a cloud of interplanetary dust particles. Three models with widely differing distributions of dust are calculated but it is not possible to distinguish between them by using existing infra-red and visible data alone.