An international team of researchers managed to measure the Sun's gravitational displacement with unprecedented accuracy. Namely, the change in the frequency of lines in the Solar Spectrum that occurs when the light leaves the gravitational field of the Sun, heading towards the Earth. The work confirms Albert Einstein's theory of relativity. About 90 years ago, he proposed a completely new concept of space-time based on a distortion felt like gravity.
The theory predicted that the light travels in curved lines near massive objects and that the Einstein Cross is seen as a consequence. These are four different images of one galaxy that is located behind a massive object, the light of which distorts perception.
Other well-known effects of the theory are associated with a gradual change in the orbit of the Mercury due to the curvature of space-time around the Sun, the shift of red lines in the spectrum of the Sun due to its gravitational shift. The latter is considered as an important effect for the efficient operation of navigation systems.
GPS sensors would not work if general relativity were not included in the equations. That effect primarily depends on the mass and radius of the space object. If it is larger for the Sun than for the Earth, it is extremely difficult to measure it in the Solar Spectrum.
Einstein's calculations in 1920 showed that the redshift is about two millionths of a wavelength. But whether that effect is actually present the astronomers do not know, and at the moment thaey are making every effort to answer that question.
To measure it, the astronomers used observations of the Solar Spectrum reflected from the lunar surface. For that, a HARPS instrument equipped with a new laser frequency comb technology was used. With its help, the researchers were able to measure the position of iron lines in the Solar Spectrum with the highest accuracy.