Abstract
Observations are described of the scattering suffered by 13 discrete sources of radio emission, having ecliptic latitudes between +15° and −29°, as they passed closest to the Sun in the 5-month interval June to October, 1960. The equipment used was an E–W interferometer with a base-line of length 2920 λ , operating at 85.5 Mc/s. It is shown that the average shape of the scattering corona over this time interval was elliptical, being more extended in equatorial than polar regions. On the average, scattering could be detected out to angular separations of about 55 R ⊙ and 40 R ⊙ in equatorial and polar regions respectively; in addition, in the equatorial regions, sporadic increases in scattering occurred out to angular separations of 120 R ⊙. Evidence is presented to show that the greater equatorial extension of the scattering corona is probably related to the active belt on the visible Sun. Detailed measurements of coronal scattering obtained by daily observation of a relatively intense radio source (MSH 12 + 08) indicated that significant changes in scattering of a random kind occurred in the interval of 24 hours between observations. This can be interpreted as due to the relative movement of the radio source and a quasi-static system of scattering regions, such as coronal rays, if temporal changes in scattering properties can be neglected. By combining the present results with earlier measurements of the scattering angles at closer angular separations, it is shown that the average scattering varies as R−2.3 out to an angular separation of 100 R ⊙ in the equatorial regions during sunspot maximum. A similar variation in the r.m.s. electron densities of the scattering irregularities is suggested if the scattering regions can be identified with extensions of the coronal rays.