Backscatter of solar resonance radiation. I.

Calculation of the angular dependence of the intensity of solar Lyman alpha resonantly scattered from neutral interstellar hydrogen which has penetrated the solar system. A simple model which essentially neglects temperature effects, but which includes gravity, radiation pressure, photoionization and charge exchange is used for this calculation. The results are then compared with the observations. The resonant scattering of He I 584 A is also treated.