256 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



and NN8.62F in the figure. The east limb crescent, containing the 

 plage areas, was observed to be six times as bright in X-ray emission 

 as the west limb crescent, which was almost clear of plage activity 

 (making allowance for the relative disk areas exposed). 



In principle. X-ray image- forming devices of high light-gathering 

 power can be achieved in the form of a grazing incidence reflection 

 telescope or a zone plate, but no such devices have yet been perfected 

 for use in rockets. Calculations, based on the intensity measured with 

 X-ray photometers and the evidence of concentrated sources derived 

 from the rocket eclipse experiment, indicated that a simple pinhole 

 camera could produce an X-ray image with a resolution of about a 

 tenth of a solar diameter during the flight time of an Aerobee-Hi 

 rocket if the camera were mounted on a pointing control to aim it 

 continuously at the sun. The first photograph of the sun in its X-ray 

 emission was obtained in this manner on April 19, 1960. The camera 

 was 6 inches long, with a pinhole of 0.005 inch in diameter. To ex- 

 clude visible and ultraviolet light, the pinhole was covered by a plastic 

 film of Parlodion, which was overcoated with an evaporated film of 

 aluminum. This combination transmitted much of the X-ray spec- 

 trum below 50 A. 



The X-ray photograph is reproduced in the upper left-hand portion 

 of figure 3. The biaxial pointing control which carried the camera 

 did not compensate for rotation about the smi-camera axis, with the 

 result that the precession of the rocket caused the image to rotate and 

 discrete features to be drawn into extended arcs. Furthermore, the 

 sense of rotation varied during the course of the flight so that the 

 image was first turned about 20° clockwise and then returned counter- 

 clockwise to complete the full arc of 160° extent. In spite of the 

 smearing thereby produced, a clear correlation could be observed be- 

 tween the X-ray emission regions and the visible plage regions on the 

 sun. 



By direct measurement of the image, the mean diameter of the 

 X-ray outline of the sun was found to be 5 percent greater than the 

 diameter of the optical disk. The maximum diameter was 6 percent 

 greater. Thus, within the limited definition of the camera, the X-ray 

 emission was observed to extend to about 0.06 solar radii (43,000 km.) 

 above the visible limb. All the measured X-ray regions in the photo- 

 graph were about the size of the resolution circle when allowance was 

 made for the smearing effect of the camera rotation. It appears that 

 the regions of strong X-ray emission are smaller than the correspond- 

 ing visible plage regions. From the fact that the sizes of the X-ray 

 regions on the limb were nearly the same as those near the center of 

 the disk, it would seem that the X-ray sources have a radial extension 

 comparable to the surface projection. 



