Improved Resolution X-ray Photographs of the Sun

Abstract

A FOURTH successful firing of the new Sun-pointed Skylark research rocket¹ took place at 0520 G.M.T. on October 20, 1965, at Woomera, Australia. The flight was designated SL 306 and on board were instruments prepared by Culham Laboratory and University of Leicester Groups for study of the short-wave-length emission of the Sun. This note presents a number of new X-ray photographs of the Sun obtained by the Leicester Group, using a camera array similar to that successfully utilized in the three earlier Skylark flights^2–4. Two significant changes in the present camera were the inclusion for the first time of a Fresnel zone plate⁵ unit and the improvement of the geometrical resolution on one pin-hole camera unit to 1 arc min. The latter improvement was encouraged by the increased exposures available from the predicted trajectory of the new, more powerful, Raven 6A rocket motor. The zone plate was flown primarily to test its rocket-worthiness prior to use in 1966 in the first Mark II stabilized Skylark, when an attempt will be made to obtain photographs of the Sun in monochromatic radiation with resolution of 10–20 arc sec. In the present flight the zone plate camera was focused for the Lyman-α line of C VI, recently⁶ found to be one of the strongest short-wavelength emission lines in the solar spectrum. Full details of the camera array are given in Table 1.