Brightening of the Solar Limb in the Far Ultra-Violet

Abstract

DURING an eclipse of the Sun, the obscuration of the disk causes a corresponding fall in the electron density in the lower layers of the ionosphere. This fall, and the subsequent recovery, have recently been used to locate the sources of ionizing radiation which were responsible for the electron production in the E- and F1-layers during the eclipse of February 25, 1952, in Central Africa¹. At this epoch the level of solar activity was fairly high, and it was found that 36 per cent of the total ionizing radiation was emitted near the east and west limbs from well-defined sources which were additional to the uniform background radiation from the disk. These sources coincided in position quite closely with areas from which the coronal line at 5303 A. was emitted strongly, and they were assumed to be associated with short-lived centres of chromospheric activity. Their intensities were so great that any permanent limb brightening which may have existed at the time would have been masked unless it was very pronounced.