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National Aeronautics and Space Administration Early Edition Age of the Universe: Cosmic Times Size of the Universe: Infinite 1919 300,000 Light Years Sun’s Gravity Bends Starlight— Einstein’s Theory Triumphs ir Joseph Thompson said, Sir Joseph made this announce stein said that the change in the “One of the greatest...of ment at a meeting of both the light’s position could be measured Sachievements in the history Royal Society and the Royal As by taking photographs of the star of human thought” was a new pre tronomical Society in London on when its light is passing close to diction Dr. Albert Einstein made. November 6, 1919. A large num the Sun, then photographed again This prediction was proven true ber of astronomers and physicists later in the year when the distant during the total eclipse of the Sun were at the meeting. Everyone star’s light is not passing close on May 29, 1919. His prediction was very excited, and they all to the Sun. These photographs was that light bends around large, agreed that observations made must be taken very carefully and massive objects like the Sun. during the eclipse proved Dr. Ein very precisely. However, what makes the predic stein’s prediction to be correct. Dr. tion different from other predic Albert Einstein is a Professor of Dr. Einstein’s General Theory of tions is that Einstein said the light Physics at the University of Ber Relativity explains that “gravity” bends around objects twice as lin and also the Director of Kaiser and “inertia” are the same. The much as what Sir Isaac Newton Wilhelm Physical Institute in Ger “force” of gravity pressing you said it should two hundred years many. down on a chair is the same force ago. you feel when the automobile you The Prediction are riding in quickly slows down, and you keep moving forward. Dr. Two hundred years ago, Sir Isaac Einstein says gravity, like inertia, Newton explained how gravity does not pull an object (this is dif works in his book, Optics. New- ferent than what Newton said). ton said if a ray of light from a Instead, anything in space that distant star passes by the edge has mass will warp and curve of a large or massive object, then both space and time around the the ray of light should be bent by object. Dr. Einstein also says that the gravity of that object. Newton the amount of curvature is directly thought gravity was a force that related to the mass of the object. pulled things toward an object. The more mass an object has, The more mass an object has, the the stronger the curve around the stronger its pull would be. The ob object. This curvature of space is ject with the largest mass near the what curves the path of light com Earth is the Sun. Based on New ing from a distant star. ton’s ideas, light from a distant As stated earlier, Dr. Einstein’s star shining just at the edge of the highly mathematical prediction Image credit: Ferdinand Schmutzer, via Wikimedia Commons Sun would be bent a very small was that the Sun’s gravity should amount by the Sun’s gravity. Ein Albert Einstein “Gravity” continued on page 2 2 “Gravity” continued from page 1 bend starlight twice as much as Newton’s earlier calculations said it should. May’s Solar Eclipse Dr. Einstein published his predic tion in Germany four years ago, in 1915, during the Great War between England and Germany. During that time, a Dutch astrono mer smuggled a copy of Dr. Ein stein’s research paper out of Eu rope and into England. Once the paper was safe in England, Arthur Stanley Eddington, the Plumar ian professor of Astronomy and Experimental Philosophy at Cam Image credit: Royal Observatory Greenwich bridge University, read Einstein’s Map showing the path of the moon’s shadow during May’s eclipse, stretching prediction. Eddington’s position at from South America to Africa. Cambridge University is the same one Newton held when he came up with his Theory of Gravity. eclipse. Sir Frank Dyson agreed, vatory, led by Dr. Crommelin, ar and sent Dr. Andrew Crommelin rived in Brazil in June of 1919 in Other astronomers had read ear and his group to northern Brazil to time to get ready for the eclipse lier versions of Einstein’s research view and photograph the eclipse. and to photograph groups of stars and already tried to test his pre in the sky. Early on the day of dictions during total solar eclipses As long as the weather was clear the eclipse, they were nervous in 1912 and 1914. However, they at one of the two places on the day because it was cloudy. But later were not successful in their at of the eclipse, it would be possible on the clouds cleared and the tempts due to cloudy weather in to take pictures. They needed to group’s observations were made 1912 and the start of the Great take pictures of the totally eclipsed with almost complete success. War in 1914. When astronomers Sun along with some of the bright The group stayed in Brazil until studied the conditions of the up stars that appeared close to the July so they could also take pic coming 1919 eclipse, it seemed Sun. tures of the same group of stars that the Sun would be in a good during a time when their light did position, right in the middle of a Results Discussed not pass by the Sun. By July, the group of bright stars. Also, the Sun had moved away from this Sun’s light would be totally blocked Later, at the meeting in London group of stars. Once they took the by the Moon for more than five in November, Sir Frank Dyson second set of photographs, they minutes, which would give pho described the work of the two returned to Greenwich, England, tographers enough time to take groups. The reason for the meet where each photographic plate pictures of the Sun and the stars ing was to decide if Einstein’s pre was carefully measured two times at the same time. diction was correct. They wanted each. to see if the light coming from the Professor Eddington decided to stars was bent (deflected) by the The other group from Cambridge lead a group to the island of Prin Sun as the stars’ light passed by University arrived on the island of cipe, near the coast of Africa, the Sun. Sir Frank said that if the Principe on April 23, 1919. But where the eclipse could be pho Sun did bend the light, the stars there were problems on the island tographed. He also convinced Sir would seem farther away from the with clouds. “We soon realized Frank Dyson, the Director of the Sun than they actually were. The that the prospects of a clear sky Royal Observatory to send an group also had to figure out how at the end of May were not very other group to a different location. far out of position the stars would good,” said Professor Eddington. This would increase their chances be on the photographic plates. At the beginning of the eclipse, of success, reducing the chance that clouds would block the The group from the Royal Obser “Gravity” continued on page 3 3 “Gravity” continued from page 2 Why a Total Solar ? the sky was completely cloudy. Eclipse About half an hour before the complete eclipse, or “totality,” the oth Sir Isaac Newton and Dr. Albert Einstein predicted that a group was able to catch glimpses ray of light from a star passing very close to the edge of the of the Sun through the clouds. BSun (as seen from Earth) will be bent, or deflected. A bend They took photographs just as in the star’s light would make the star look slightly farther away from they had planned, but only two the edge of the Sun than it really is. out of the 16 photographic plates showed enough stars to measure. Dr. Einstein’s Theory of Relativity predicts that the amount of deflec Unlike the group from the Royal tion should be twice as much as the amount of deflection Newton Observatory who stayed until predicted. July to take a second set of pho tographs, the Cambridge Univer The astromers would get better accuracy of their measurements the sity group was not able to stay on more stars there were near the Sun in the sky during the eclipse. Principe Island to take a second They would also get better results the more pictures they could take set of photographs to compare during the eclipse. This would give them better accuracy when the first photos to. comparing Dr. Einstein’s predictions to Newton’s predictions. Each year, on May 29th, as the Earth revolves around the Sun, the Sun During the meeting, Sir Frank ex appears to pass in front of a cluster of stars in the constellation Tau plained how they made observa rus. The cluster of stars, called Hyades, is so bright that they are tions, the equipment they used, clearly visible without a telescope during the winter in the night sky. and how the photographic plates were measured back at the Green wich Observatory. He also talked The only way this star cluster could be viewed on May 29th would about how the star positions dur be if the Sun was totally eclipsed and its light was blocked. On May ing the eclipse compared to their 29, 1919, a total eclipse happened, which allowed Dr.

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