Astronomer Biography 2

Joseph Fraunhofer

Fraunhofer was born in Straubing, Bavaria, in 1787, and was orphaned at the age of 11. He was taken in and apprenticed to Philipp Anton Weichelsberger, a unpleasant glassmaker, but in 1801, the shop where he worked collapsed while he was inside. Maximilian IV Joseph (the future king of Bavaria, Maximilian I Joseph) led the rescue operation, entering into Fraunhofer's life. The Prince provided him with books and forced Weichelsberger to allow the young Fraunhofer time to study.

Then in 1806 two other glassmakers, Utzscheider and Georg von Reichenbach, brought Fraunhofer to their Institute, a Benedictine monastery that specialized in glass making. It was there that he discovered how to make optical glass, as well as invent extremely precise methods for measuring dispersion. By 1818, he had became the director of the Optical Institute.

During this time, in 1814, Fraunhofer invented the spectroscope, and, while researching the light-bending properties of different types of glass, noticed dark lines in the light spectrum of a sodium fire. That bright line that had appeared in the orange color of the spectrum, led him to begin experimenting to determine whether the solar spectrum contained the same bright line in the orange like it did in the fire. Fraunhofer plotted hundreds of spectral lines, and by measuring their wavelengths found that the positions of the lines were constant, and didn't matter whether they were produced by the direct rays of the Sun or by reflected light from the Moon or planets. This led him to discover 574 dark fixed lines in the solar spectrum. Today we know that there are millions of such fixed absorption lines.

After his discoveries, in 1815, he designed several heliometers, that were eventually used by the German astronomer Friedrich Bessel, who made the first measurement of the distance between a star, 61 Cygni, and Earth. After studying the work of James Gregory, who identified the foundation of diffraction grating, and David Rittenhouse who invented the first man-made diffraction grating, he developed his own diffraction grating in 1821. Fraunhofer discovered that the spectra of first-magnitude stars, like Sirius, differed from the sun and from each other, thus founding stellar spectroscopy.

Unfortunately, like many glassmakers of his era, Fraunhofer died young, at the age of 39, due to heavy metal vapor poisoning.

The dark lines that Fraunhofer discovered were later found to be atomic absorption lines, as Kirchhoff and Bunsen explained in 1859. These lines are still called Fraunhofer lines in his honor and its said that his discovery went far beyond the few divisions in the solar system's spectrum that had been previously discovered.