Solar spectrum, dark lines

In 1817, Josef Fraunhofer (1787-1826) studied the spectrum of solar radiation, observing a continuous spectrum with numerous dark lines. Fraunhofer labeled the most prominent of the dark lines with letters. In 1859, Gustav Kirchhoff (1824-1887) showed that the D line in the solar spectrum was due to the absorption of solar radiation by sodium atoms. The wavelength of the sodium D line is 589 nm. What are the frequency and the wavenumber for this line ... 

Spectroscopy is generally considered to have started in 1666, with Newton s discovery of the solar spectrum. Wollaston repeated Newton s experiment and in 1802 reported that the sun s spectrum was intersected by a number of dark lines. Fraunhofer investigated these lines—Fraunhofer lines—further and, in 1823, was able to determine their wavelengths. 

Kirchhoff and Bunsen concluded, after extensive joint observations, that the dark lines of the solar spectrum which are not evoked by the atmosphere of the earth exist in consequence of the presence, in the... 

Newton s spectrum of the sun showed the colours spread out in a continuous band. 1802 WOLLASTON [4] introduced a slit about 1 mm broad and viewed the slit through a prism. He saw the solar spectrum crossed by a number (a small number) of dark bands. It is difficult to be certain what bands these were, but it seems likely that one of them - in the yellow - might be attributed today to sodium. This, then, would have been the first time that the sodium D lines had claimed the attention of an observer. 

So, then, Fraunhofer observed and labelled characteristic and recognisable dark lines in the solar spectrum and gave us the wavelengths of many of them. But what were these lines and why were they there ... 

Since the atmosphere shields us from most deep ultraviolet radiation and from infrared radiation, the bulk of visible light (the solar spectrum) ranges from 350 to 750 nm. The 25,000 Frauenhofer15 "dark" lines are interruptions (in the range 295 to 1000 nm) in the continuous solar emission spectrum, due to absorption by the chemical elements present in the sun s atmosphere. Ultraviolet radiation was discovered by Ritter16 in 1801. Some radio waves do penetrate the earth s atmosphere, and they are most intense during solar storms. Infrared radiation also penetrates to some extent. 

Figure 24F-1 The solar spectrum. The dark vertical lines are the Fraunhofer lines. See color plate 18 for a full-color version of the spectnim. Images created by Dr. Donald Mickey, University of Hawaii Institute for Astronomy, from National Solar Observatory spectral data. NSOS/Kitt Peak FTS data used here were produced by NSF/NOAO.

Color plate 1 7 The solar spectrum, (a) Expanded color version of the solar spectrum shown in black and white in Feature 24-1 (Figure 24F-1). The huge number of dark absorption lines are produced by all of the elements in the sun. See if you can spot some prominent lines like the famous sodium doublet. 

Figure 9.1 Solar irradiance at the surface of the Earth. The dark lines denote the bandgap energies of Si, GaAs, CdS and SrXi03, respectively at T = 300 K. The portions of the spectrum to the left of each line represent photons that are not substantially absorbed by the semiconductor.

A.7.8 The dark lines in the solar spectrum are caused by elements in the sun s atmosphere that absorb at those specific wavelengths. The existence of helium was demonstrated in the Sun s atmosphere before it was found on the Earth. The dark lines of helium in the solar spectrum had the same pattern as the emission spectrum of elemental helium discovered on the Earth. 

In 1868 the French physicist Pierre Janssen detected a new dark line in the solar emission spectrum that did not match the emission lines of known elements. The name helium (from the Greek helios, meaning the sun) was given to the element responsible for the absorption line. Twenty-seven years later, helium was discovered on Earth by the British chemist William Ramsay in a mineral of uranium. On Earth, the only source of helium is through radioactive decay processes—a particles emitted during nuclear decay are eventually converted to helium atoms. 

I) The sun consists of an incredibly hot centre (above 10 6 K) surrounded by a relatively cool layer at about 5800 K. If the sun is examined by a hand spectroscope, the solar spectrum is seen to contain some dark lines, Fraunhofer Unes, superimposed upon a continuous blend of rainbow colours. What causes the dark lines ... 

Solar spectrum as well as line emission spectra characteristic of a series of metals (all spectra in black and white rather than color). The lines (bands) of the pure metals are emission lines from each metal. The solar spectrum lines (top) are lines of darkness in the continuous rainbowlike solar spectrum. These Fraunhofer lines (only the most intense are shown) arise from absorption of solar light by the corresponding metal present in the solar photosphere. Fraunhofer lines labeled A, a, B are due to absorption by O2 in the Earth s atmosphere. 

Fraunhofer lines Dark lines in the solar spectrum that result irom the absorption by elements in the solar chromosphere of some of the wavelengths of the visible radiation emitted by the hot interior of the sun. 

The development of emission spectroscopy was a long process initiated by Descartes in 1637 with his illustration that white light can be decomposed into its components with a prism. Several scientists later observed dark lines in the solar spectrum (e.g., Wollaston in 1802). Their constancy was noted and they were mapped in detail by Fraunhofer in 1814. He also noted the appearance of colored, changing lines from other sources. Talbot in 1826 correlated the appearance of some lines with the presence of certain elements. Similar observations were described later by other scientists without arousing much interest at the time. In this context the work of Alter is significant, he produced the first spectral atlas, a tabulation relating spectral lines to chemical elements, in 1854. 

Emission spectroscopy achieved complete scientific recognition owing to the work of Bunsen and Kirchhoff, who, in their famous lecture in 1859, described their construction of the spectroscope and its application to the identification of elements (Figure 6). They built this by quite simply using two telescopes, one without the eyepiece lenses, which were replaced by a slit, a prism, and a mirror. Various flames, in which materials were suspended, were used for excitation. In later papers Kirchhoff explained the reasons for the appearance of dark and bright lines in the solar spectrum, and Bunsen proved the power of the method by reporting the discovery of two new elements, cesium and rubidium. In the following... 

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