In 1905 Albert Einstein published his first paper on special relativity, a revolutionary idea which shook the foundations of the scientific world. The concept that time is relative and not fixed was completely novel, and initially no one had any idea how to prove or disprove it; Einstein's own work depended heavily on what he called "thought experiments."
In 1916 Einstein published his theory of general relativity, which included his ideas on how gravity works. In the process of completing his theory of general relativity, which includes the now-famous E=mc2 equation, Einstein said that since mass and energy are interrelated, light should bend in the presence of sufficient gravity, and he calculated the exact magnitude of that bending based on his theory. The eclipse of 1919 provided the first opportunity to test this prediction. Two different observatories measured the deflection of starlight as it passed by the sun during the eclipse. This confirmation of the theory of relativity made the front page of many major newspapers, and made Einstein something of a celebrity. Observation of another solar eclipse in 1922 confirmed the 1919 measurements.