Albert Einstein experienced and contributed to many important events during his 50-year career as a theoretical physicist. Still, few moments had as great an impact on his life than a solar eclipse that occurred in March of 1919 -- and Einstein wasn't even there to see it.

The eclipse, documented by British astronomer Sir Arthur Eddington off the west coast of Africa, was important because it helped prove Einstein's General Theory of Relativity.

One of Einstein's greatest, yet most abstract theories, the General Theory of Relativity, states that the force of gravity should affect light in much the same way it affects matter. The theory predicts that light should curve when in the presence of a strong gravitational field, such as the one created by our sun.

While Einstein was convinced of the validity of his theory, and even predicted how it might be proved, many people, including other physicists, found no reason to suggest that it was true. Isaac Newton's conclusions that light always travels in a straight line had not been disproved in more than 200 years.

In March of 1919, however, Sir Arthur Eddington's observations and photographs changed all that. Einstein had predicted that, if it was possible to view stars whose light passes quite near the sun, they should appear to be in a different place than where they actually are. This is because the light they emit would be bent as it passed through the sun's gravitational field. To prove such an idea, however, would require seeing the stars in the presence of the sun, or during the day -- an impossibility, except during a solar eclipse.

Eddington's photographs, taken during the 1919 eclipse, showed stars nearest the sun in positions different from those they occupied at night, in the sun's absence. The pictures were proof that light could, in fact, be affected by gravity, providing an important step toward the general acceptance of Einstein's General Theory of Relativity.