Behaviour of Ultra-Violet and Daylight Rays in the Solar Cycle

Abstract

WHEN graphs are constructed, for the sunspot cycle 1933–44, of the annual averages both of ultraviolet and of daylight rays, they are found to have a decisive minimum at the sunspot maximum, of 1937–38, and the drop from maximum to minimum of the daylight curves is approximately twice as large as that of the ultra-violet curves. This drop of the rays received at the time when the sun has its highest activity, as shown by the maximum number of spots, suggests that the rays emitted from the sun are in part absorbed in their passage to the earth by some agency which fluctuates with the sun's activity and is most effective at the time of maximum sunspots. The ionization of the upper air due to ultra-violet rays is a probable agency in producing this effect.