Joseph von Fraunhofer
Joseph von Fraunhofer (March 6, 1787 – June 7, 1826) was a German optician who was the first to study and classify the dark lines in the light spectrum that bear his name. During his lifetime he was known as the maker of the finest refractor telescopes, and practically momopolized the market for fine instruments of that type. He also perfected the use of fine gratings for producing and analyzing spectra.
Biography
Fraunhofer was born in Straubling, Germany. His father is said to have been a glass grinder by trade, and when both his parents died at the age of 11, he started working as an apprentice to a harsh glassmaker named Philipp Anton Weichelsberger. In 1801 a house in which he lodged collapsed, and he was trapped in the rubble. the workshop in which he was working collapsed and he was buried in the rubble. The rescue operation was led by Maximilian IV Joseph, Prince Elector of Bavaria (the future Maximilian I Joseph). The prince entered Fraunhofer's life, providing him with books and forcing his employer to allow the young Joseph Fraunhofer time to study.
After eight months of study, Fraunhofer went to work at the Optical Institute at Benediktbeuern, a secularised Benedictine monastery devoted to glass-making. There he discovered how to make the world's finest optical glass and invented incredibly precise methods for measuring dispersion. In 1818 he became the director of the Optical Institute. Due to the fine optical instruments he had developed, Bavaria overtook England as the centre of the optics industry. Even the likes of Michael Faraday were unable to produce glass that could rival Fraunhofer's.
His illustrious career eventually earned him an honorary doctorate from the University of Erlangen in 1822. In 1824, he was awarded the order of merit, became a noble, and made an honorary citizen of Munich. Like many glassmakers of his era who were poisoned by heavy metal vapors, Fraunhofer died young, in 1826 at the age of 39. His most valuable glassmaking recipes are thought to have gone to the grave with him.
Scientific research
In 1814, Fraunhofer invented the spectroscope, and discovered 574 dark lines appearing in the solar spectrum. These were later shown to be atomic absorption lines, as explained by Kirchhoff and Bunsen in 1859. These lines are still sometimes called Fraunhofer lines in his honour.
He also invented the diffraction grating and in doing so transformed spectroscopy from a qualitative art to a quantitative science by demonstrating how one could measure the wavelength of light accurately. He found out that the spectra of Sirius and other first-magnitude stars differed from each other and from the sun, thus founding stellar spectroscopy.
Ultimately, however, his primary passion was still practical optics, once noting that "In all my experiments I could, owing to lack of time, pay attention to only those matter which appeared to have a bearing upon practical optics."
Fraunhofer lines
The Fraunhofer lines are a set of spectral lines named after Fraunhofer. The lines were originally observed as dark features (absorption lines) in the optical spectrum of the Sun.
In 1802, English chemist William Hyde Wollaston was the first person to note the appearance of a number of dark features in the solar spectrum. In 1814, Fraunhofer independently rediscovered the lines and began a systematic study and careful measurement of the wavelength of these features. In all, he mapped over 570 lines, and designated the principal features with the letters A through K, and weaker lines with other letters.
It was later discovered by Gustav Kirchhoff and Robert Bunsen that each chemical element was associated with a set of spectral lines, and deduced that the dark lines in the solar spectrum were caused by absorption by those elements in the upper layers of the sun. Some of the observed features are also caused by absorption in oxygen molecules in the Earth's atmosphere.
The major Fraunhofer lines, and the elements they are associated with, are shown in the following table:
| Designation | Element | Wavelength (nm) | Designation | Element | Wavelength (nm) | |
|---|---|---|---|---|---|---|
| y | O2 | 898.765 | c | Fe | 495.761 | |
| Z | O2 | 822.696 | F | H β | 486.134 | |
| A | O2 | 759.370 | d | Fe | 466.814 | |
| B | O2 | 686.719 | e | Fe | 438.355 | |
| C | H α | 656.281 | G' | H γ | 434.047 | |
| a | O2 | 627.661 | G | Fe | 430.790 | |
| D1 | Na | 589.592 | G | Ca | 430.774 | |
| D2 | Na | 588.995 | h | H δ | 410.175 | |
| D3 (or d) | He | 587.5618 | H | Ca+ | 396.847 | |
| e | Hg | 546.073 | K | Ca+ | 393.368 | |
| E2 | Fe | 527.039 | L | Fe | 382.044 | |
| b1 | Mg | 518.362 | N | Fe | 358.121 | |
| b2 | Mg | 517.270 | P | Ti+ | 336.112 | |
| b3 | Fe | 516.891 | T | Fe | 302.108 | |
| b4 | Fe | 516.751 | t | Ni | 299.444 | |
| b4 | Mg | 516.733 |
Given their well-defined wavelengths, Fraunhofer lines are often used to characterize the refractive index and dispersion properties of optical materials.[1]
See also
- Optics
- Spectroscopy
- Fraunhofer line
- Timeline of solar astronomy
- Balmer series
Notes
- ↑ The Fraunhofer C-, F-, G'-, and h- lines correspond to the alpha, beta, gamma and delta lines of the Balmer series of emission lines of the hydrogen atom. The D1 and D2 lines form the well-known "sodium doublet," the center wavelength of which (587.5618 nm) is given the designation letter "D." There is disagreement in the literature for some line designations; e.g., the Fraunhofer d-line may refer to the cyan iron line at 466.814 nm, or alternatively to the yellow helium line (also labeled D3) at 587.5618 nm. Similarly, there is ambiguity with reference to the e-line, since it can refer to the spectral lines of both iron (Fe) and mercury (Hg). To resolve ambiguities that arise in usage, ambiguous Fraunhofer line designations are preceded by the element with which they are associated (e.g., Mercury e-line and Helium d-line).
ReferencesISBN links support NWE through referral fees
- Aller, Lawrence H. (1991). Atoms, Stars and Nebulae, 3rd ed.. Cambridge University Press. ISBN 0-521-32512-9.
External links
Credits
New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:
The history of this article since it was imported to New World Encyclopedia:
Note: Some restrictions may apply to use of individual images which are separately licensed.
