May 04

What’s Up in the Sky

What’s Up in the Sky – May, 2019

Einstein’s Eclipse

One hundred years ago everything changed. Not all at once, not even as the years progressed, but by the end of the twentieth century what had begun on May 29, 1919 would dominate our technology. For it was on that day that a total solar eclipse captured the attention of the scientific community and introduced a new scientific theory to the public all over the world. It also propelled a little known scientist named Albert Einstein to international fame.

In 1915, as the First World War raged throughout Europe, Einstein published four revolutionary papers on general relatively, an extension of his earlier theory of special relativity, that showed that spacetime is connected to matter. He used his new theory to correct a flaw in Newton’s law of gravity that incorrectly calculated a certain aspect of the orbit of Mercury. General relatively predicted the orbit precisely.

But the scientific community was not convinced and another test was needed, this one to measure the amount of deflection of light by a massive object, the basis of “gravitational lensing” widely used today, and a method suggested by Einstein in 1911. All scientists needed was an opportunity to measure the precise positions of stars near the Sun’s disc. If the bending did exist then stars appearing close to the Sun would be in a slightly different position compared to where they normally are. This can only be accomplished during a total solar eclipse when the nearby stars become visible.

Several unsuccessful attempts were made following Einstein’s 1911 calculations of the bending, and it was fortunate for him that they were, for had they accurately measured the bending, it would have been different than his earlier predictions. But when, in 1915, he recalculated the deflection based on general relativity, the numbers turned out to be spot on. Had the earlier observations been successful, Einstein’s place in history might have been very different.

The war negated eclipse viewing opportunities in 1916 and 1918, but in March of 1919, just four months after the war’s end, Arthur Stanley Eddington, then director of the Cambridge Observatory, set out from Liverpool to Principe, an island off the West African coast. Meanwhile, a second group of distinguished astronomers traveled to northern Brazil for their observations and measurements.

Eddington’s journey to Principe was a grueling six and a half weeks by steamship, only made tolerable by an abundance of bananas, a delicacy to the rationing-weary Englishmen. The other team’s trip to Brazil with 14 crates of heavy equipment took two weeks, followed by a month’s delay before they could travel to their destination, about 50 miles inland.

On the day of the eclipse there was tension at both sites due to the threatening weather. The Brazil team was fortunate that the weather finally cleared and they were able to make accurate measurements. Eddington’s team was not as lucky but were still able to gather important data.

Upon returning to England and after several months of painstaking analysis, both teams determined that the amount of bending of the light was precisely what Einstein’s theory had predicted!

These experiments were daring, provided clear evidence, promised a scientific revolution, and gave people a much sought after positive story following four brutal years of war. Although no single experiment could prove relativity, the theory has been tested and confirmed countless times over the past century.

On July 2, 2019, another total solar eclipse will be visible from nearly the same locations, almost acting as a tribute to the centenary of the eclipse that revealed to us how the universe actually works.

For a more in depth description of this fascinating event, I recommend the article, A Relatively Important Eclipse, by Benjamin Skuse in the May, 2019, issue of Sky and Telescope magazine.

This month in history:
May 5: Alan Shepard becomes first American in space – 1961
May 9: Hyabusa, the first spacecraft to bring back a sample from an asteroid, is launched – 2003
May 11: Launch of first geostationary weather satellite – 1974
May 12: Adler Planetarium in Chicago opens, first planetarium in western hemisphere – 1930
May 14: Skylab is launched – 1973
May 25: President Kennedy gives speech challenging nation to land an astronaut on the Moon before the end of the decade – 1961
May 29: First experimental test of Einstein’s General Theory of Relativity successfully performed during total solar eclipse – 1919