GRAVITATIONAL-RADIATION AND VERY LONG-BASE-LINE INTERFEROMETRY

Gravitational waves affect the observed direction of light from distan t sources. At telescopes, this change in direction appears as periodic variations in the apparent positions of these sources on the sky; tha t is, as proper motion. A wave of a given phase, traveling in a given direction, produces a characteristic pattern of proper motions over th e sky. Comparison of observed proper motions with this pattern serves to test for the presence of gravitational waves. A stochastic backgrou nd of waves induces apparent proper motions with specific statistical properties, and so may also be sought. In this paper we consider the e ffects of a cosmological background of gravitational radiation on astr ometric observations. We derive an equation for the time delay measure d by two antennae observing the same source in an Einstein-de Sitter s pacetime containing gravitational radiation. We also show how to obtai n similar expressions for curved Friedmann-Robertson-Walker spacetimes .