Contour plots of the equivalent width (in angstroms) of heliospheric Lyα absorption as a function of LISM H I column depth (N_H) and line of sight. We assume a LISM model with b = 9.3 km s⁻¹, v = −29 cos θ km s⁻¹. The variable N_H is given by the distance to the origin, in the scale marked on both the abscissa and ordinate, as in a polar plot. The angle θ in the polar plot is the angle between the nose direction and the sight line to potential stellar targets. The sight lines to 36 Oph, α Cen, and 31 Com, at θ = 12°, 52°, and 72°, respectively, are indicated by dotted lines. Model 1 results (supersonic inflow) are shown in (a), and model 2 results (subsonic inflow) are in (b). Model 3 is intermediate to these. The GHRS echelle A can easily resolve a total absorption corresponding to the 0.008 Å contour.