The deflection of light induced by the Sun's gravitational field and measured with geodetic VLBI

TL;DR

This paper demonstrates that geodetic VLBI can measure the Sun's gravitational light deflection across the entire sky, providing a continuous test of general relativity beyond eclipse observations.

Contribution

It shows that VLBI measurements can detect the Sun's gravitational light deflection as an annual motion of radio sources, extending tests of relativity beyond traditional eclipse-based methods.

Findings

Radio sources exhibit annual circular motion proportional to ecliptic latitude.

Deflection effect is equivalent to gravitational delay in VLBI data reduction.

Current VLBI precision is sufficient to measure the light deflection effect.

Abstract

The Sun's gravitational field deflects the apparent positions of close objects in accordance with the formulae of general relativity. Optical astrometry is used to test the prediction, but only with the stars close to the Sun and only during total Solar eclipses. Geodetic Very Long Baseline Interferometry (VLBI) is capable of measuring the deflection of the light from distant radio sources anytime and across the whole sky. We show that the effect of light deflection is equivalent to the gravitational delay calculated during the reduction of VLBI data. All reference radio sources display an annual circular motion with the magnitude proportional to their ecliptic latitude. In particular, radio sources near the ecliptic pole draw an annual circle with magnitude of 4 mas. This effect could be easily measured with the current precision of the geodetic VLBI data.