Session 1, Page 11: Different Types of Spectra


Robert Bunsen and Gustav Kirchoff were a pair of chemists who in 1859 began studying the spectra of gasses produced by different chemical elements when burned in a laboratory flame. They detected a series of lines in these spectra as well, but instead of dark lines on a bright background, they found bright lines on a dark background. While in the process of cataloging the bright emission spectra for all of the then known elements, Kirchoff found that he was able to match the series of bright lines in the laboratory spectra to the dark lines found in the solar spectrum. This was the first evidence that the Sun contained many of the same elements found on Earth.

Kirchoff's Laws: There are three types spectra, as illustrated in Figure 15. An emission line spectrum is produced by a hot, thin gas. Such were the spectra produced in the laboratory experiments conducted on the chemical elements by Bunsen and Kirchoff . A continuous spectrum is produced by a hot, dense object, while an absorption line spectrum is the result of the light from a hot, dense object passing through a cloud of cooler, less dense gas. This is the type of spectrum produced by the Sun as the extremely hot, dense inner material of the Sun radiates its energy in the form of light through its cooler outer atmosphere.	Figure 15 The three types of spectra. Diagram courtesy Brown University.

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