Observations of the He II 304-A radiation in the night sky

The intensity and spatial variations of the He II 304–A radiation in the night sky were measured to an altitude of 264 km from a sounding rocket launched from Thumba, India, on March 10, 1970. The data obtained are presented in the form of an all-sky map and are compared with theoretical predictions. The data are not consistent either with diffusive equilibrium models of exospheric helium or with plausible models of helium in the interplanetary medium. The data can be fit with a constant density plasmasphere model bounded at the magnetic shell L = 4 in combination with a tenuous gas of helium ions in the plasma sheet. Numerical results obtained with this model are compared with in situ satellite observations.