Deflection of Light By A Gravitational Field

Deflection of Light By A Gravitational Field

December 5, 2019

According to the general theory of relativity, a ray of light will experience the curvature of its path passing through a gravitational field, this curvature being similar to that experienced by a path of a body that is projected through a gravitational field. As a result of this theory, we should expect that a ray of light which is passing close to a heavenly body would be deviated towards the latter for a ray of light which passes the sun at a distance of ∆sun radii from its center, the deflection of (a) should amount to;

a= 1.7 seconds of arc/∆

It may be added that according to the theory half of this deflection is produced by the Newtonian field of attraction of the sun, and the other half by the geometrical modification of the space caused by the sun.

This result admits of an experimental test by the means of the photographic registration of stars during the total eclipse of the sun. The only reason why we must wait for a total eclipse is that at every of the time that the atmosphere is strongly illuminated by the light of the from the sun that the stars situated near the sun’s disc are invisible. The predicted effect can be seen clearly from the accompanying diagram.

If the sun was not present, a star that is practically infinitely distance would be seen in the direction D1, as observed from the earth. But as a consequence of the deflection of the light from the star by the sun, stars will be seen in the direction D2 that is at the somewhat greater distance from the center of the sun then corresponds to an absolute position.

In practice, the question is tested in the following way. The stars in the neighborhood of the sun photographed during a solar eclipse.

In addition, second photographs of the same stars taken when the sun is situated at another position in the sky that is a few months earlier or later. As compared to the standard photograph the positions of the stars on the eclipse photograph ought to appear displaced radially outward by an amount corresponding to the angle a.

I am heartily indebted to the Royal Society and the Royal Astronomical Society for the investigation of this important detection. The results of the measurements confirmed the theory in a satisfactory manner. The rectangular components of the observed and of the calculated deviations of the star ( in seconds of arc) are set forth in the following table of results;

Prepared By: Prajjwal Jha, Moonlight Secondary School Kumaripati, Lalitpur.