Helium Resonance Radiation in the Night and Day Sky.

Abstract

The intensities expected from the helium resonance lines scattered by interplanetary and terrestrial helium are estimated. The apparent emission rates for these lines from the interplanetary medium are very small (4ir1 ~ 1 R), since it appears that helium flowing from the sun does not have time to recombine. Hence, helium in the interplanetary medium is probably predominantly Heiii. The emissions from the upper atmosphere have been estimated on the basis of assumptions concerning the escape of atmospheric helium. Very little emission is expected on the night side GirI~10R), but on the day side, an observer looking down from several earth radii should see a substantial amount of N584 Hei. A mean of 4irI(X584: day) 103R is found, which could be as high as 1400R with the sun in the zenith.