Everything about Fraunhofer Lines totally explained
In
physics and
optics, the
Fraunhofer lines are a set of
spectral lines named for the German physicist
Joseph von Fraunhofer (
1787–
1826). The lines were originally observed as dark features (
absorption lines) in the
optical spectrum of the
Sun.
The English chemist
William Hyde Wollaston was in
1802 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. Modern observations of
sunlight can detect many thousands of lines.
It was later discovered by
Kirchhoff and
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're 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 |
Hβ |
486.134 |
| A |
O2 |
759.370 |
d |
Fe |
466.814 |
| B |
O2 |
686.719 |
e |
Fe |
438.355 |
| C |
Hα |
656.281 |
G' |
Hγ |
434.047 |
| a |
O2 |
627.661 |
G |
Fe |
430.790 |
| D1 |
Na |
589.592 |
G |
Ca |
430.774 |
| D2 |
Na |
588.995 |
h |
Hδ |
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 |
516.891 |
t |
Ni |
299.444 |
| b4 |
Mg |
516.733 |
|
|
|
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 D
1 and D
2 lines form the well-known "sodium doublet", the centre wavelength of which (589.29 nm) is given the designation letter "D".
Note that there's disagreement in the literature for some line designations; for example, the Fraunhofer d-line may refer to the
cyan iron line at 466.814 nm, or alternatively to the
yellow helium line (also labeled D
3) at 587.5618 nm. Similarly, there's ambiguity with reference to the e-line, since it can refer to the spectral lines of both iron (Fe) and mercury (Hg). In order to resolve ambiguities that arise in usage, ambiguous Fraunhofer line designations are preceded by the element with which they're associated (for example, Mercury e-line and Helium d-line).
Because of their well defined wavelengths, Fraunhofer lines are often used to characterize the
refractive index and
dispersion properties of optical materials.
Further Information
Get more info on 'Fraunhofer Lines'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://fraunhofer_lines.totallyexplained.com">Fraunhofer lines Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
