Elizabeth Landau of NASA –
Over one hundred years ago, on May 29, 1919, astronomers observed a total solar eclipse in an ambitious effort to test Albert Einstein’s general theory of relativity by seeing it in action. Essentially, Einstein thought space and time were intertwined in an infinite “fabric,” like an outstretched blanket. A massive object such as the Sun bends the spacetime blanket with its gravity, such that light no longer travels in a straight line as it passes by the Sun.
This means the apparent positions of background stars seen close to the Sun in the sky — including during a solar eclipse — should seem slightly shifted in the absence of the Sun, because the Sun’s gravity bends light. But until the eclipse experiment, no one was able to test Einstein’s theory of general relativity, as no one could see stars near the Sun in the daytime otherwise.