Submillimetre brightness spike at the solar limb

Abstract

WE report here the first complete phase of the reduction of data obtained during the solar eclipse of June 30, 1973 from the high altitude moving platform provided by Concorde 001. Reports of the flight¹ and of an optical measurement of chromospheric thickness² are already published. Submillimetre observations were made at both the second and third contacts, using a rapid-scanning Michelson interferometer. At the second contact one complete interferogram of resolution 1 cm⁻¹ was measured each second, but the limited passband of the detector, an InSb Rollin instrument³, was found to have attenuated the highest frequencies (above 200 Hz) so these data have not been used. At the third contact 10 s were taken per interferogram. The instrument response was satisfactory, but the record needed subsequent digitisation, rendering analysis much lengthier, since an electronic analogue Fourier transformer had been built for 1 s interferograms, but was not usable for the 10 s data.