  We propose a new method to constrain the actual state of the interstellar
cloud that surrounds the solar system. Using Voyager UVS Lyman-alpha sky maps
and the powerful principle of invariance, we derive the H distribution all
along the spacecraft path. Provided current models of the heliopause interface
between the solar and the interstellar winds, we extrapolate this distribution
to farther distances from the Sun and infer in a self consistent way key
parameters of the local cloud.
