Transit of Mercury across the solar disk

Abstract

THE transit of Mercury across the solar disk on May 9, 1970 (4 h 20 min 30 s – 11 h 12 min 0 s UT), was observed by recording the radio emission at a wavelength of 8 mm using a 22-m paraboloid radio telescope¹. The pencil beam of the antenna is of width D = 1′.6 and the sensitivity of the radiometer ≃ 1.5 K. The antenna was steered so that Mercury was in the centre of the beam. Mercury obscures the inhomogeneities of radio emission when passing across the solar disk and some fluctuations of the flux of radio emission can occur. The characteristic time of these fluctuations and their amplitude characterise the sizes and temperatures of condensations respectively. In Fig. 1 we show a sample of original (averaged over 15 s) records of fluctuations during the passage of Mercury across the relatively active regions on the disk. Similar records, but with slightly slower fluctuations of smaller amplitude have been obtained for quiet regions of the disk. The autocorrelation curves for active (A) and quiet (Q) regions (Fig. 2) reveal details of the nature of the emission.