Galactic and extragalactic contributions to the far-ultraviolet background

Data from the 1350--1550 A bandpass channel of the 20.5 angular resolution extreme-ultraviolet telescope on the Apollo-Soyuz mission have been analyzed for stellar airglow radiation contributions for the galactic latitude range Vertical BarbVertical Bar>300. At intermediate latitudes the resulting diffuse background is found to be correlated with the neutral hydrogen column density as determined by 21 cm radio data. This result, together with the observed anisotropy and mean intensity of the radiation field, is consistent with the hypothesis that scattering of galactic-plane starlight off dust grains having an albedo aapprox. =0.5 and a phase function coefficient gapprox. =0.5 is the primary source of the observed radiation field at the intermediate latitudes. The background intensity near the poles is, however, higher than expected from the H I column density and extinction measurements. Taking into account all sources observed during the mission, we find the energy density of the radiation field at 1440 A in the solar neighborhood to be 7.3 +- 3 x 10-17 ergs cm-3 A-1, a value in rough accordance with recent theoretical expectations