Chapter 1.6 The bending of Light

The first prediction put to test was the apparent bending of light as it passes near a massive body. This effect was conclusively observed during the solar eclipse of 1919, when the Sun was silhouetted against the Hyades star cluster, for which the positions were well known.

Sir Arthur Eddington stationed himself on an island off the western coast of Africa and sent another group of British scientists to Brazil. Their measurements of several of the stars in the cluster showed that the light from these stars was indeed bent as it grazed the Sun, by the exact amount of Einstein's predictions. Einstein became a celebrity overnight when the results were announced.

The apparent displacement of light results from the warping of space in the vicinity of the massive object through which light travels. The light never changes course, but merely follows the curvature of space. Astronomers now refer to this displacement o f light as gravitational lensing.

But the Sun's gravity is relatively weak compared with what's out there in the depths of space. In the dramatic example of gravitational lensing below, the light from a quasar (a young, distant galaxy that emits prodigious amounts of radio energy) 8 billion light years away is bent round by the gravity of a closer galaxy that's "only" 400 million light years distant from Earth.