Dear Eclipse Hater…
By Nelia Mann
The phrase “scientific community” gets thrown around a lot. But the thing is, it really is a community. We don’t just rely on each other professionally. We form friendships and maintain relationships, even across national borders, and across oceans. We have our own culture, with its particular value system. We have our own history, our own heroes, villains, noble quests. And a solar eclipse is like our very own holiday. Something we can share with the whole world, but which has a special meaning to us, as scientists, being woven into our common history and into many of our personal journeys.
In 1919, Sir Arthur Eddington took advantage of a solar eclipse over the island of Principe to try prove one of the central predictions of Einstein’s theory of general relativity: the bending of light near a massive body. He wanted to measure the deflection of starlight by our Sun — the problem being that you usually can’t see stars whose light passes right by the sun, because the sun itself is too bright. Unless, of course, there’s a solar eclipse. Later, Eddington’s results were questioned; it is not clear that his measurements were accurate enough to warrant the claims he made. Since then we have had plenty of other confirmations of Einstein’s work, but it was Eddington’s results that made Einstein an international celebrity. Newspapers and the public alike were captivated by sheer strangeness of Einstein’s theories, and the romance of a British astronomer working to confirm the predictions of a German physicist so soon after the end of World War I.
My own first eclipse fell on July 22, 1990, when I was eleven. I got the plans for constructing a pinhole camera from National Geographic World, and made one from an old cardboard box. When I discovered I would be away at summer camp for the event and might miss it, I had a near meltdown until my parents promised me they would arrange with the summer camp to ensure I could be outside to view the eclipse. The strange thing is, I don’t even remember the event itself. I do remember (with some embarrassment) writing a letter to the magazine, wondering about celestial alignments other than solar and lunar eclipses. I had confused mathematics with physics, and counted out six possible permutations of the Sun, Moon, and Earth. I did not notice that two of these permutations are impossible, and of the other four there are really only two distinct physical options.
Sir Arthur Eddington was not the first scientist to try to use an eclipse to verify Einstein’s theories. Five years earlier, Erwin Finlay-Freundlich and his team set off for Crimea, loaded down with observing equipment. Unfortunately for him, World War I broke out while he was en route, and found him, a German national carrying all sorts of cameras, trekking through Russian territory. He spent several days as a prisoner of war before being packed off back home in an exchange of prisoners. Actually, this may have been for the best. Einstein’s definitive theory of relativity wasn’t published until 1915, so Finlay-Freundlich was working off of an earlier version, which actually gets the deflection of light wrong. Had Finlay been successful, and had he discovered the discrepancy, it might have endangered or delayed the acceptance of Einstein’s theories.
I was in high school the next time I found myself near a solar eclipse. By this time I was too busy pretending to be cool to plan ahead, and it caught me off guard. I was late for class when I happened to pass under a tree, and saw the crescent-shaped sun dapples formed by the partially occluded sunlight as it passed through the leaves. I stopped, stared, and entirely forgot the consequences of ditching class. This being before the advent of the ubiquitous smartphone, I did not respond in the now-traditional manner of capturing the event on camera, and posting it triumphantly on the internet. Instead, after dragging the moment out as long as possible, I slunk back inside and prepared my excuses for when the school called my parents.
Though the story of Einstein’s general relativity and its confirmation via eclipse is probably the most famous, it isn’t the only instance of an eclipse playing a crucial role in scientific discovery. In 1868, French astronomer Pierre Jules César Janssen was in India for a solar eclipse, measuring the “spectrum” of the Sun during the event: the particular wavelengths of light present in the sunlight. He discovered, in addition to the familiar spectrum associated with hydrogen, the more complicated spectrum of another, previously unknown element. That element came to be called helium, after the Greek word Helios, for “Sun.” It is produced in the Sun’s core through the fusion of hydrogen, though it would be more than half a century before that process was fully understood.
Tomorrow I set off on a road trip that will land me in Carbondale, IL, to watch this summer’s big event. I won’t be attempting to prove the validity of general relativity, or to discover helium. Instead, I will just be a common celebrant, there to remember glories of eclipses past and recapture the wonder of youth for a few minutes. Maybe it’s just an excuse for a bit of time off, a party, and an adventure. But then, isn’t that what most holidays are?[In response to Confessions of an Eclipse Hater]
Nelia Mann is a professor of physics at Union College. Her research focuses on string theory.