The Gravitational Lens Effect

The so-called gravitational lens effect, previously worked out by Tikhov in 1937, is derived in a simple manner. The effect is caused by the gravitational deflection of light from a star S in the gravitational field of another star By and occurs when S lies far behind B , but close to the line of sight through B . It turns out that a considerable increase in the apparent luminosity of S is possible. A method is given to determine the mass of a star which acts as a gravitational lens. The possibility of observing the effect is discussed.