Spectrum and Fraunhofer Lines
Explanation1 2 3 4
A spectrum refers to the object of study in spectroscopy, which is light decomposed into various colors. The first spectrum picture one often sees is a line spectrum like the one above, either long horizontally or vertically. However, the spectrum was not always in this form. The first person to discover that light could be decomposed into various colors through a prism was Newton. Because Newton passed the light through a small hole and then again through a prism, the spectrum obtained in this manner was circular shaped as shown below.
Later, the British physicist William Hyde Wollaston developed a method to observe the spectrum in a rod shape by passing light through a slit, which is a narrow and long hole, instead of a small hole and then decomposing it with a prism. Because line spectra are easier to observe, it allowed for more precise analysis. While observing the spectrum of sunlight in this way, Wollaston discovered a phenomenon in which black lines appeared vertically at certain positions. This meant that sunlight did not contain light of certain colors (wavelengths). Wollaston did not show much interest in this phenomenon, but Joseph von Fraunhofer looked into it more closely. Fraunhofer was a person who made great achievements in the optical industry at the precision equipment company of Joseph von Utzschneider, a high-ranking German official. With his superior technology, Fraunhofer conducted more precise research on the solar spectrum.
The picture above is the solar spectrum personally drawn and colored by Fraunhofer. Fraunhofer discovered that the solar spectrum contained more black lines than Wollaston had observed. Wollaston had observed only a few lines, but Fraunhofer found as many as 574 lines. Fraunhofer named these lines from A to Z based on their wavelength and position, which is still used today. These lines are referred to as Fraunhofer Lines.
While continuing his research, Fraunhofer noticed that the line he named D appeared in the spectrum of a spectroscopic experiment with sodium. Later, the French physicist Jean Bernard Leon Faucault discovered that when sunlight passed through sodium gas and its spectrum was observed, the D line appeared more clearly. This meant that sodium gas absorbed the light of the wavelength that shows the D spectrum. Subsequent research by the German scientists Gustav Kirchhoff and Robert Wilhelm Bunsen revealed not only that sodium absorbs the D spectrum, but also emits it.
These research findings have made it possible to identify specific elements present in any substance through spectrum analysis. For example, by analyzing the spectrum of light from a certain star, one can determine which elements the star contains, among other uses in various scientific fields.