This year– 2014– marks the 200th anniversary of many important events. The last war between nations on North American soil reached a crescendo when the Brits and Canadians burned down the White House in Washington. Louis XVIII was invited to reoccupy the French throne after Napoleon’s exile. And eight people were killed by the London Beer Flood in which a domino effect of ruptured vats released 1.4 million liters of beer into the streets. But an event of more lasting importance occurred in the labs of an astute German optician, Joseph von Fraunhofer, who discovered a series of gaps in the rainbow spectrum of the Sun that gave the first hints of what stars were made of.
Joseph von Fraunhofer was born in 1787 into a family of expert glassmakers, and he appeared to be on the fast track to a successful life making decorative glassware for wealthy patrons. But his luck turned for the worse when he was orphaned at age 11, then shipped off to apprentice with a demanding and dour master glassmaker. When the master’s house accidentally collapsed on young Fraunhofer, nearly killing him, the scene attracted the attention of Prince Maximilian Joseph, who took a liking to the boy and became his benefactor. The prince kept Fraunhofer’s hard-hearted master at bay and made sure the young man had access to further education. It worked. By the time Fraunhofer was 19 years old, he was making not glass baubles for the wealthy, but the best telescope lenses the world had yet seen.
(In a way, Fraunhofer’s story reminds me somewhat of the tale of young E.E. Barnard, a young American astronomer who started life under even more dire circumstances).
Fraunhofer continued to improve his glass and lensmaking skills. But he also invented an amazingly useful instrument called a spectroscope, a combination of a diffraction grating and a small telescope which precisely separated light into its constituent colors. He used the device to measure how light refracted through his lenses. In those days before electric light, Fraunhofer used the Sun as a bright light source. But Fraunhofer found a surprising thing with his spectroscope. He found the continuous spectrum of the Sun, the colors of light we see when sunlight passes through a prism, were riddled with hundreds of dark gaps or “lines” (see image at top of page).
Many great discoveries in science result not with a scientist running down the street yelling “Eureka!”. They are made with a keen-eyed observer like Fraunhofer looking at his measurements and saying “that’s funny…” (as in that’s strange and unexpected).
Fraunhofer had no way to explain the origin of these lines– the science had not been invented yet. The explanation came later in the 19th century from the labs of his fellow Germans Robert Bunsen and Gustav Kirchhoff, who discovered the Fraunhofer lines were caused by light absorbed by chemical elements such as iron and calcium and sodium in the atmosphere of the Sun. The Sun– and the stars– are made of the same elements found on our planet.
Fraunhofer died young, at age 39, of tuberculosis which may have been worsened by glassblowing. He was trained as an artisan, not a scientist, so he wrote down very little of his techniques and took his trade secrets to the grave.
More about Fraunhofer’s work in this excellent short video: