The 1919 Eclipse Results

In 1919 the British observations did not go smoothly either in Brazil or on Principe, but the altered positions of the target stars were still measurable on the photographic plates exposed.

The astronomers did not immediately break camp and head back to England to announce their results. First they had to wait

FIGURE 4-6. Sailors of the U.S. Navy, having labored to erect the instruments to view a total solar eclipse, pose with astronomers in Spain early in the 1900s.

some months before again photographing the star fields at night, when the Sun was far away, so that the space through which the starlight traveled was not warped by the solar gravity. It was only by directly comparing the two sets of plates that the subtle shifts in the stellar positions would be discernable. They were looking for a differential shift of less than one second of arc; even on a perfectly still night, the amount of scintillation or blurring shown by stars due to atmospheric turbulence is of this order. (Recall the nursery rhyme: "Twinkle, twinkle, little star, how I wonder what you are.")

It was November of 1919 before the outcome of the eclipse analysis was made public, with great fanfare in London. Einstein was right, Dyson and Eddington said, and it was front-page news around the globe.

In subsequent years data collected at other eclipses has clearly confirmed that the deviation of starlight is just as Einstein anticipated. For instance, photographs taken from Mauritania during the great eclipse of 1973 (as plotted in Figure 2-2) again demonstrated that the stellar displacements are larger than Newtonian physics would allow. Measurements using large arrays of radio telescopes have shown that the gravitational deflection of starlight is within one percent of Einstein's value. These and other experiments have shown that Einstein's GTR gives a better representation of the universe than Newton's theory of gravity. Nevertheless, it is possible that there are refinements yet to be discovered.

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