Scientists are looking forward to scientific opportunities they will have as the continental United States gets to witness a total solar eclipse on Aug. 21.

It will not be the first time that researchers will be taking advantage of this rare celestial phenomenon. A groundbreaking experiment during an earlier total eclipse that occurred nearly 100 years ago, in fact, helped confirm Albert Einstein's theory of relativity.

Einstein's Theory Of General Relativity Versus Isaac Newton's Model Of Classical Mechanics

Four years before the May 29, 1919 total solar eclipse, Einstein published four papers introducing the theory of general relativity. The theoretical physicist, however, was hardly known at the time.

Einstein's work faced skepticism as Isaac Newton's model of classical mechanics, which was formulated in 1687, dominated scientific understanding.

Einstein's theory, which predicted that space and time were relative and form a four-dimensional continuum called space-time, was not consistent with Newton's views. Einstein proposed that gravity is a manifestation of the curvature of space-time. Objects travel through this space-time fabric, which can be warped, bent and twisted by the motions and masses of objects within space-time.

1919 Total Solar Eclipse Tested Einstein's General Theory Of Relativity

All masses cause a curvature of space-time but the effect is very subtle, and testing Einstein's theory would call for very massive objects like stars. The opportunity came with the 1919 total solar eclipse, when Arthur Eddington performed the first experimental test on the general theory of relativity.

The eclipse would happen just as the sun was crossing a bright star cluster. Astronomers realized that the starlight would have to pass through the gravitational field of the sun on its way to Earth and could be seen because of the darkness of the eclipse. This would make it possible for astronomers to make accurate measurements of the gravity-shifted positions of the stars in the sky.

Eddington first measured the initial positions of the stars in January and February 1919. By May, he went to a remote island of Principe to measure the positions of the stars during the eclipse. Other astronomers also took measurements from another location in Brazil.

The two locations were fortunate to have clear skies during the eclipse allowing the astronomers to take several pictures of the six-minute total eclipse. The data later confirmed Einstein's predictions.

While the warped space-time only deflected the light so slightly and could not be seen by the naked eye, the observations were found to agree with Einstein's predictions. It was proven that the warping of space-time by the mass of the sun was real.

The findings were announced in November 1919 and made Einstein a celebrity.

"A key result of Einstein's theory is that matter warps space-time, and thus a massive object can cause an observable bending of light from a background object. The first success of the theory was the observation, during a solar eclipse, that light from a distant background star was deflected by the predicted amount as it passed near the sun," NASA said.

Gravitational Lensing

The bending of light around massive objects is now called gravitational lensing, which has since become an important tool used by astrophysicists. Scientists also use gravitational lensing to study dark matter and the expansion of the universe.

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