Precise measurement of the solar gravitational red shift

We present the concept and the status of a multi-year project based on a new method to measure the Gravitational Red Shift of the Solar Spectrum with high precision. This project is aimed to conduct experimental verifications of the effect that the Einstein theory of General Relativity predicts for the frequencies of the Fraunhofer lines, that is, the light spectrum emitted by the Sun in its strong gravitational field. Previous determinations of such effect is limited to a precision of 2%. In order to discriminate between classical and relativistic explanations, we need to be sensitive to one part per million of the predicted effect. We have developed a new powerful technique, the Magneto-Optical Filter, that is able to provide far better precision and, for the future, possible space instrumentations able to extend our test to the second-order effect of the relativistic equivalence principle, never done before. The present paper is intended to describe the instrumentation, the procedure and the first encouraging results.