Gravitational Lensing by a Point Mass

Gravitational lensing was first predicted by Albert Einstein's general theory of relativity and confirms that gravity changes the shape of spacetime, causing light rays to be bent. Strong lensing creates multiple images from a source. A lens that is axially symmetric will create an image of a ring, called the Einstein ring, when the source is directly behind the lens. The first observation of a lensing effect with the Sun as the lens was in 1919 [1] and the first lensing event by a galaxy was observed in 1979 [2].

For further reading see:

[1] F. W. Dyson, A. S. Eddington, and C. Davidson, "A Determination of the Deflection of Light by the Sun's Gravitational Field, from Observations Made at the Total Eclipse of May 29, 1919," Philosophical Transactions of the Royal Society of London, 220, 1920 pp. 291–333.


[2] D. Walsh, R. F. Carswell, and R. J. Weymann, "0957 + 561 A, B—Twin Quasistellar Objects or Gravitational Lens," Nature, 279, 1979 pp. 381-384.


[3] R. Narayan and M. Bartelmann, "Lectures on Gravitational Lensing," 1996.