Over the last 100 years or so, our view of the universe has changed dramatically.  It was possible in the early 20th century to think that our galaxy (literally meaning Milky Way, same root as “lactose” and “lactate”) might be the entire universe.  The famous “Great Debate” between astronomers Harlow Shapley and Heber Curtis was over whether the observed “spiral nebulae” were part of our galaxy, or separate galaxies in their own right. The issue wasn’t settled during the debate, but several years later by Edwin Hubble, who used techniques developed by Henrietta Swan Leavitt to measure the distance to the Andromeda galaxy.  Needless to say, he found the distance to be much larger than the size of the Milky Way, thus showing the universe to be a very large place.

Edwin Hubble (1889-1953) and Henrietta Swan Leavitt (1868-1921)

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Posted by Matthew R. Francis under Director's Notes & Science Ideas & Science News | No Comments »

On this date (May 29) in 1919, Arthur Stanley Eddington and his crew traveled to the island of Príncipe off the coast of Africa to observe a total solar eclipse. Solar eclipses, which occur when the Moon’s shadow falls on Earth, aren’t all that rare, but this one was important: it was the first total eclipse after the First World War, and the first after Albert Einstein predicted the bending of light by gravity. In other words, the gravity of the Sun (and indeed any massive object) will affect the path that light takes from distant stars. As one of the most significant predictions of Einstein’s general theory of relativity (first published in 1916), the bending of light due to gravity needed precise measurements to prove it was happening.

Usually, though, the Sun’s light overwhelms the light from stars, so the effect of gravity is not detectable under ordinary circumstances—which is why Eddington needed to make his observations during a solar eclipse, when the Moon blocks much of the Sun’s light from reaching Earth. The effect of gravity showed up by comparing the position of stars during the eclipse to their position when the Sun is in a different part of the sky—the bending of light by the Sun makes the stars appear in different places.  (Sizes and positions are exaggerated for clarity!)

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