Europe is set to experience its first total solar eclipse in over 25 years on August 12. The astronomical spectacle will begin in the Russian Arctic, arc across Greenland, and conclude in Spain, offering millions a glimpse of a rare sky show.
A total solar eclipse is a significant event not only for public viewing but also for scientific observation. Historically, eclipses have provided unique opportunities to test fundamental scientific theories. One of the most notable experiments occurred on May 29, 1919. Four years prior, in November 1915, Albert Einstein had presented his theory of general relativity, which posited that gravity can warp space-time and bend light around massive objects like the sun. Einstein calculated that starlight passing near the sun would be diverted by approximately 1.75 arc seconds, a minuscule deflection that would be imperceptible without the dimming effect of an eclipse.
To verify Einstein's predictions, two astronomical expeditions, one from the Greenwich Observatory and another from Cambridge University, were dispatched to Sobral, Brazil, and the island of Principe off the west coast of Africa, respectively. These locations were chosen because they lay within the path of the 1919 eclipse. During the brief period of totality, the astronomers precisely charted the positions of stars that became visible near the sun. In the evenings following the eclipse, after the sun had set, they mapped the same stars again. Their observations confirmed that the star positions differed slightly from those recorded during the eclipse, providing crucial early evidence supporting Einstein's theory of general relativity.