100 Years Since Solar Eclipse that Proved Relativity Theory

Solar eclipse

MAY 29, 1919

Today we celebrate exactly a hundred years since probably for science the most important solar eclipse in human history. It was on Thursday. The total eclipse lasted 6 minutes and 51 seconds, long enough to test Einstein's prediction of space-time deformation due to gravity, causing the light to bend.


In 1915 Einstein wrote in his Theory that gravity causes the universe to curve. Following the curve, light from stars should bend as well. Therewith the light of the stars near the sun is bend by the sun's gravity. The problem is, that stars near the sun are not visible to us. The only way to test and empirically prove Einstein's light-bending prediction of nearby stars is during a solar eclipse when the sun is darkened and the stars near it visible.


In 1919 the Newton`s law of universal gravity still dominated the scientific discourse. Arthur Stanley Eddington was among the first physicists to recognize the importance of Einstein's general theory of relativity. He organized the expedition to the Island Principe in West Africa, where the full eclipse was visible.

At the end of May, the sun is in the middle of the open cluster of the Hyades (star cluster), which was an exceptionally favorable constellation for this experiment.

The positions of the stars near the sun confirmed the Theory. The red dot on the picture shows the location where the star on the picture would be if the sun`s gravity didn't cause its light to bend.

Light bending of a star near the sun. Image Courtesy: Royal Observatory, Greenwich

The deformation of space-time by the sun's mass was empirically proved. Newton's static space theory was replaced, making Einstein and his new Theory of Relativity famous also among non-scientists.​

©2020 by Stellar Milieux