EINSTEIN EQUATIONS IN THE NULL QUASISPHERICAL GAUGE

Properties of the Einstein equations in a coordinate gauge based on ex panding null hypersurfaces foliated by metric 2-spheres are described. This null quasispherical (NQS) gauge leads to particularly simple ana lyses of the characteristic structure of the equations and of the prop agation of gravitational shocks, and clarifies the geometry of timelik e boundary condition. A feature of the NQS gauge is the use of the sta ndard partial derivative ('edth') operator on S-2 to express angular d erivatives, and the consequent use of spin-weighted spherical harmonic decompositions of the metric fields.