Interplanetary Gas. VI. on Diffuse Extreme Ultraviolet Helium Radiation in the Night and Day Sky.

The intensities expected from the lines X 304 He ii and X 584 He I due to resonance scattering by helium in the earth's upper atmosphere and the interplanetary medium are estimated. The apparent emission rates for these lines from the interplanetary medium are very small AirI < 1R), since it appears that the helium flowing from the sun does not have time to recombine. Hence helium in the interplanetary medium is probably predominantly He iii. The emissions from the upper atmosphere have been estimated on two different assumptions concerning the method of escape of atmospheric helium. If helium escapes as He I, we would expect a day intensity (observing from several earth radii looking down) in X 584 He I corresponding to 4iri 10 R. If He ii is important in the escape of atmospheric helium, the day intensity could correspond to 4iri( 304) 10R. The emission rate expected on the night side in these lines is rather small, 4irI < 10R.