100th Anniversary of the 1919 Solar Eclipse

In 1915, Einstein published the first paper on his general theory of relativity, which is nowadays used to describe gravitation. Many scientists were critical about this theory at the time, largely because it used very complex mathematics. To test the theory, Einstein proposed three experiments, the so-called classical tests of general relativity: the perihelion precession of Mercury’s orbit, the deflection of light by the Sun and the gravitational redshift of light.


Scientists then executed the second experiment in 1919. To view stars that are close to the Sun, the experiment could only be done during a total solar eclipse.  Measurements were therefore done on 29 May 1919, during a solar eclipse, in the north of Brazil and on the Principe Island, off the coast of Equatorial Guinea in West Africa. British astronomer Sir Arthur Stanley Eddington was in charge of this second expedition. He was fascinated by Einstein's theory and was eager to discover the applicability of the theory, which he also promoted among the scientists of the Royal Astronomical Society. The results of the expeditions followed in November and were very promising. They seemed greatly compatible with Einstein’s theory and extensively different from the Newtonian one.


Today, many more experiments have been executed to test Einstein's theory, which is widely used in modern physics and astrophysics. The theory is praised for its beauty, simplicity and symmetry. A phenomenon predicted by Einstein in 1916 using this theory, has only recently (in February 2016) been detected: gravitational waves. While observing two merging black holes, the Advanced LIGO team managed to directly detect the gravitational waves.

How to get involved?

Explore the following projects that celebrate this special IAU100 Milestone: